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  • Weitere Quellen  (36.024)
  • NASA Technical Reports  (36.024)
  • LUNAR AND PLANETARY EXPLORATION  (14.409)
  • AERODYNAMICS  (12.790)
  • FLUID MECHANICS AND HEAT TRANSFER  (8.825)
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  • 101
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    Planetary loss from light ion escape on Venus (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-04-02
    Beschreibung: Using Pioneer Venus data, hydrogen and deuterium ions are shown to escape from the hydrogen bulge region in the nightside ionosphere. The polarization electric field propels these light ions upward through the ionosphere and into the ion-exosphere, where H(+) and D(+) continue to be accelerated away from Venus and move into the ionotail and beyond. The vertical flow speeds of H(+) and D(+) are found to be about the same; therefore, selective escape between H(+) and D(+) is negligible for this mechanism. Present day planetary loss rates of about 8.6 x 10(exp 25)/s and 3.2 X 10(exp 23)/s were obtained for H(+) and D(+), respectively. Such rates, persisting over a few billion years, should have significantly affected the planetary water budget.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Advances in Space Research (ISSN 0273-1177); 15; 4; p. (4)117-(4)122
    Format: text
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  • 102
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    A 3-D Navier-Stokes CFD study of turbojet/ramjet nozzle plume interactions at Mach 3.0 and comparison with data (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: Advanced airbreathing propulsion systems used in Mach 4-6 mission scenarios, usually consist of a single integrated turboramjet or as in this study, a turbojet housed in an upper bay with a separate ramjet housed in a lower bay. As the engines transition from turbojet to ramjet, there is an operational envelope where both engines operate simultaneously. One nozzle concept under consideration has a common nozzle, where the plumes from the turbojet and ramjet interact with one another as they expand to ambient conditions. In this paper, the two plumes interact at the end of a common 2-D cowl, when they both reach an approximate Mach 3.0 condition and then jointly expand to Mach 3.6 at the common nozzle exit plane. At this condition, the turbojet engine operated at a higher NPR than the ramjet, where the turbojet overpowers the ramjet plume, deflecting it approximately 12 degrees downward and in turn the turbojet plume is deflected 6 degrees upward. In the process, shocks were formed at the deflections and a shear layer formed at the confluence of the two jets. This particular case was experimentally tested and the data used to compare with the PARC3D code with k-kl two equation turbulence model. The 2-D and 3-D centerline CFD solutions are in good agreement, but as the CFD solutions approach the outer sidewall, a slight variance occurs. The outer wall boundary layers are thin and do not present much of an interaction, however, where the confluence interaction shocks interact with the thin boundary layer on the outer wall, strong vortices run down each shock causing substantial disturbances in the boundary layer. These disturbances amplify somewhat as they propagate downstream axially from the confluence point. The nozzle coefficient (CFG) is reduced 1/2 percent as a result of this sidewall interaction, from 0.9850 to 0.9807. This three-dimensional reduction is in better agreement with the experimental value of 0.9790.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Lewis Research Center, HBCUs Research Conference Agenda and Abstracts; p 35
    Format: text
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  • 103
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    Simulation of crossflow instability on a supersonic highly swept wing (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A direct numerical simulation (DNS) algorithm has been developed and validated for use in the investigation of crossflow instability on supersonic swept wings, an application of potential relevance to the design of the High-Speed Civil Transport (HSCT). The algorithm is applied to the investigation of stationary crossflow instability on an infinitely long 77-degree swept wing in Mach 3.5 flow. The results of the DNS are compared with the predictions of linear parabolized stability equation (PSE) methodology. In-general, the DNS and PSE results agree closely in terms of modal growth rate, structure, and orientation angle. Although further validation is needed for large-amplitude (nonlinear) disturbances, the close agreement between independently derived methods offers preliminary validation of both DNS and PSE approaches.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-198267 , NAS 1.26:198267 , NIPS-96-08486
    Format: application/pdf
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  • 104
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    Wavenumber selection and hysteresis in nonlinear baroclinic flow (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Wavenumber transition and hysteresis in a highly unstable baroclinic flow are investigated using a high-resolution spectral numerical model. As the flow becomes more supercritical, the dominant wave gradually shifts from the most unstable wave predicted by the linear theory to a longer wave with a larger time-averaged amplitude, while the rectified mean flow attains a stronger shear at the center of the channel. The numerical results display a complex hysteresis behavior, which occurs not only between the states of different dominant wavenumbers, but also between the states of identical dominant wavenumber but of different dynamic characteristics. In a certain parameter range three stable states, each with different dominant wavenumber, are possible, and in another parameter range four stable states are possible, among them three stable states with an identical dominant wave. The numerical results suggest that a multiple weather regime exists even without external forcing in which the flow aperiodically varies between two distinct behaviors. The effects of stable higher harmonics are assessed and it is found that their presence contributes not only to the better approximation of the model solutions but also to the selection of the final equilibrium state, due to the chaotic nature of the initial transient period.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-111211 , NAS 1.15:111211 , NIPS-96-07276
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  • 105
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    Volumetric imaging of supersonic boundary layers using filtered Rayleigh scattering background suppression (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: We demonstrate the use of Filtererd Rayleigh Scattering and a 3D reconstruction technique to interrogate the highly three dimensional flow field inside of a supersonic inlet model. A 3 inch by 3 inch by 2.5 inch volume is reconstructed yielding 3D visualizations of the crossing shock waves and of the boundary layer. In this paper we discuss the details of the techniques used, and present the reconstructured 3D images.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 94-0491 , Development of Filtered Rayleigh Scattering for Accurate Measurement of Gas Velocity; 8 p
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  • 106
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    Distribution and nature of UV absorbers on Triton's surface (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Substantial evidence suggests that a UV spectrally Absorbing Material (UV-SAM) exists on Triton's surface. This evidence is found in the positive slope in Triton's spectrum from the UV to the near-IR, and the increasing contrast in Triton's light curve in the blue and UV. Although it is now widely-thought that UV-SAMs exist on Triton, little is known about their distribution and spectral properties. The goal of this NDAP Project is to determine the spatial distribution and geological context of the UV-SaM material. We hope to determine if UV-SAMs on Triton are correlated with geologic wind streaks, craters, calderas, geomorphic/topographic units, regions containing (or lacking) volatile frosts, or some other process (e.g., magnetospheric interactions). Once the location and distribution of UV-SAMs has been determined, further constraints on their composition cable made by analyzing the spectrographic data set. To accomplish these goals, various data sets will be used, including Voyager 2 UV and visible images of Triton's surface, IUE and HST spectra of Triton, and a geologic map of the surface based on voyager 2 and spectrophotometric data. The results of this research will be published in the planetary science literature.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-199361 , NAS 1.26:199361 , SWRI PROJ. 15-5653
    Format: application/pdf
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  • 107
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    Ground-recorded sonic boom signatures of F-18 aircraft formation flight (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Two F-18 aircraft were flown, one above the other, in two formations, in order for the shock systems of the two aircraft to merge and propagate to the ground. The first formation had the canopy of the lower F-18 in the inlet shock of the upper F-18 (called inlet-canopy). The flight conditions were Mach 1.22 and an altitude of 23,500 ft. An array of five sonic boom recorders was used on the ground to record the sonic boom signatures. This paper describes the flight test technique and the ground level sonic boom signatures. The tail-canopy formation resulted in two, separated, N-wave signatures. Such signatures probably resulted from aircraft positioning error. The inlet-canopy formation yielded a single modified signature; two recorders measured an approximate flattop signature. Loudness calculations indicated that the single inlet-canopy signatures were quieter than the two, separated tail-canopy signatures. Significant loudness occurs after a sonic boom signature. Such loudness probably comes from the aircraft engines.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-104312 , H-2067 , NAS 1.15:104312
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  • 108
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    On the consistency of Reynolds stress turbulence closures with hydrodynamic stability theory (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The consistency of second-order closure models with results from hydrodynamic stability theory is analyzed for the simplified case of homogeneous turbulence. In a recent study, Speziale, Gatski, and MacGiolla Mhuiris showed that second-order closures are capable of yielding results that are consistent with hydrodynamic stability theory for the case of homogeneous shear flow in a rotating frame. It is demonstrated in this paper that this success is due to the fact that the stability boundaries for rotating homogeneous shear flow are not dependent on the details of the spatial structure of the disturbances. For those instances where they are -- such as in the case of elliptical flows where the instability mechanism is more subtle -- the results are not so favorable. The origins and extent of this modeling problem are examined in detail along with a possible resolution based on rapid distortion theory (RDT) and its implications for turbulence modeling.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198173 , NAS 1.26:198173 , ICASE-95-46
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  • 109
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    Nonlinear (time domain) and linearized (time and frequency domain) solutions to the compressible Euler equations in conservation law form (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Two linearized solvers (time and frequency domain) based on a high resolution numerical scheme are presented. The basic approach is to linearize the flux vector by expressing it as a sum of a mean and a perturbation. This allows the governing equations to be maintained in conservation law form. A key difference between the time and frequency domain computations is that the frequency domain computations require only one grid block irrespective of the interblade phase angle for which the flow is being computed. As a result of this and due to the fact that the governing equations for this case are steady, frequency domain computations are substantially faster than the corresponding time domain computations. The linearized equations are used to compute flows in turbomachinery blade rows (cascades) arising due to blade vibrations. Numerical solutions are compared to linear theory (where available) and to numerical solutions of the nonlinear Euler equations.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199398 , NAS 1.26:199398
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  • 110
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    Nozzle Flow with Vibrational Nonequilibrium (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Flow of nitrogen gas through a converging-diverging nozzle is simulated. The flow is modeled using the Navier-Stokes equations that have been modified for vibrational nonequilibrium. The energy equation is replaced by two equations. One equation accounts for energy effects due to the translational and rotational degrees of freedom, and the other accounts for the affects due to the vibrational degree of freedom. The energy equations are coupled by a relaxation time which measures the time required for the vibrational energy component to equilibrate with the translational and rotational energy components. An improved relaxation time is used in this thesis. The equations are solved numerically using the Steger-Warming flux vector splitting method and the Implicit MacCormack method. The results show that uniform flow is produced outside of the boundary layer. Nonequilibrium exists in both the converging and diverging nozzle sections. The boundary layer region is characterized by a marked increase in translational-rotational temperature. The vibrational temperature remains frozen downstream of the nozzle, except in the boundary layer.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199948 , NAS 1.26:199948 , NIPS-95-06856
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  • 111
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    Sweeping and straining effects in sound generation by high Reynolds number isotropic turbulence (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The sound radiated by isotropic turbulence is computed using inertial range scaling expressions for the relevant two time and two point correlations. The result depends on whether the decay of Eulerian time correlations is dominated by large scale sweeping or by local straining: the straining hypothesis leads to an expression for total acoustic power, whereas the sweeping hypothesis leads to a more recent result.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198235 , NAS 1.26:198235 , ICASE-95-77 , NIPS-95-06838
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  • 112
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    Computational Study of Flow Establishment in a Ram Accelerator (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The temporal evolution of the combustion process established during projectile transition from the launch tube into the ram accelerator section containing an explosive hydrogen-oxygen-argon gas mixture is studied. The Navier-Stokes equations for chemically reacting flow are solved in a fully coupled manner, using an implicit, time accurate algorithm. The solution procedure is based on a spatially second order total variation diminishing scheme and a temporally second order, variable-step, backward differentiation formula method. The hydrogen-oxygen chemistry is modeled with a 9-species, 19-step mechanism. The accuracy of the solution method is first demonstrated by several benchmark calculations. Numerical simulations of two ram accelerator configurations are then presented. In particular, the temporal developments of shock-induced combustion and thrust forces are followed. Positive thrust is established in both cases; however, in one of the ram accelerator configurations studied, combustion in the boundary layer enhances its separation, ultimately resulting in unstart.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-107068 , NAS 1.15:107068 , E-9931 , ICOMP-95-20 , AIAA PAPER 95-2489 , NIPS-95-06486
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  • 113
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    Methodology for simulation of unsteady flows to determine the time-dependent interference between stationary and moving boundaries (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient for the required man-hours.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199779 , NAS 1.26:199779 , NIPS-95-06450
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  • 114
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    Shape optimization of single- and two-element airfoils on multiblock grids (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A multiblock, discrete sensitivity analysis method is used to couple a direct optimization method and a flow analysis method. The domain is divided into smaller subdomains for which the sensitivities are obtained separately. Then, an effective sensitivity equation is solved to complete the coupling of all the sensitivity information. The flow analysis is based on the thin-layer Navier-Stokes equations solved by an implicit, upwind-biased, finite-volume method. The method of feasible directions is used for the present gradient-based optimization approach. First, a transonic airfoil is optimized to investigate the behavior of the method in highly nonlinear flows as well as the effect of different blocking strategies on the procedure. A supercritical airfoil is produced from an initially symmetric airfoil with multiblocking affecting the path but not the final shape. Secondly, a two-element airfoil is shape optimized in subsonic flow to demonstrate the present method's capability of shaping aerodynamically interfering elements simultaneously. For a very low and a very high Reynolds number cases, the shape of the main airfoil and the flap are optimized to yield improved lift-to-drag ratios.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-199785 , NAS 1.26:199785 , AIAA PAPER 94-4273 , NIPS-95-06444
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  • 115
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    User's manual for the one-dimensional hypersonic experimental aero-thermodynamic (1DHEAT) data reduction code (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A FORTRAN computer code for the reduction and analysis of experimental heat transfer data has been developed. This code can be utilized to determine heat transfer rates from surface temperature measurements made using either thin-film resistance gages or coaxial surface thermocouples. Both an analytical and a numerical finite-volume heat transfer model are implemented in this code. The analytical solution is based on a one-dimensional, semi-infinite wall thickness model with the approximation of constant substrate thermal properties, which is empirically corrected for the effects of variable thermal properties. The finite-volume solution is based on a one-dimensional, implicit discretization. The finite-volume model directly incorporates the effects of variable substrate thermal properties and does not require the semi-finite wall thickness approximation used in the analytical model. This model also includes the option of a multiple-layer substrate. Fast, accurate results can be obtained using either method. This code has been used to reduce several sets of aerodynamic heating data, of which samples are included in this report.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-4691 , NAS 1.26:4691
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  • 116
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    Computation of rotor-stator interaction using the Navier-Stokes equations (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The numerical scheme presented belongs to a family of codes known as UNCLE (UNsteady Computation of fieLd Equations) as reported by Whitfield (1995), that is being used to solve problems in a variety of areas including compressible and incompressible flows. This derivation is specifically developed for general unsteady multi-blade-row turbomachinery problems. The scheme solves the Reynolds-averaged N-S equations with the Baldwin-Lomax turbulence model.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199424 , NAS 1.26:199424
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  • 117
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    Multiple scales approach to weakly nonparallel and curvature effects: Details for the novice (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A multiple scales approach is used to approximate the effects of nonparallelism and streamwise curvature on the stability of three-dimensional disturbances in incompressible flow. The multiple scales approach is implemented with the full second-order system of equations. A detailed exposition of the source of all terms is provided.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198199 , NAS 1.26:198199
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  • 118
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    On High-Order Radiation Boundary Conditions (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: In this paper we develop the theory of high-order radiation boundary conditions for wave propagation problems. In particular, we study the convergence of sequences of time-local approximate conditions to the exact boundary condition, and subsequently estimate the error in the solutions obtained using these approximations. We show that for finite times the Pade approximants proposed by Engquist and Majda lead to exponential convergence if the solution is smooth, but that good long-time error estimates cannot hold for spatially local conditions. Applications in fluid dynamics are also discussed.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198404 , E-9918 , NAS 1.26:198404 , ICOMP-95-15
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  • 119
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    Design geometry and design/off-design performance computer codes for compressors and turbines (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: This report summarizes some NASA Lewis (i.e., government owned) computer codes capable of being used for airbreathing propulsion system studies to determine the design geometry and to predict the design/off-design performance of compressors and turbines. These are not CFD codes; velocity-diagram energy and continuity computations are performed fore and aft of the blade rows using meanline, spanline, or streamline analyses. Losses are provided by empirical methods. Both axial-flow and radial-flow configurations are included.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-198433 , NAS 1.26:198433 , E-10041 , NIPS-95-06493
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  • 120
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    Analytical and phenomenological studies of rotating turbulence (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A framework, which combines mathematical analysis, closure theory, and phenomenological treatment, is developed to study the spectral transfer process and reduction of dimensionality in turbulent flows that are subject to rotation. First, we outline a mathematical procedure that is particularly appropriate for problems with two disparate time scales. The approach which is based on the Green's method leads to the Poincare velocity variables and the Poincare transformation when applied to rotating turbulence. The effects of the rotation are now reflected in the modifications to the convolution of a nonlinear term. The Poincare transformed equations are used to obtain a time-dependent analog of the Taylor-Proudman theorem valid in the asymptotic limit when the non-dimensional parameter mu is identical to Omega(t) approaches infinity (Omega is the rotation rate and t is the time). The 'split' of the energy transfer in both direct and inverse directions is established. Secondly, we apply the Eddy-Damped-Quasinormal-Markovian (EDQNM) closure to the Poincare transformed Euler/Navier-Stokes equations. This closure leads to expressions for the spectral energy transfer. In particular, an unique triple velocity decorrelation time is derived with an explicit dependence on the rotation rate. This provides an important input for applying the phenomenological treatment of Zhou. In order to characterize the relative strength of rotation, another non-dimensional number, a spectral Rossby number, which is defined as the ratio of rotation and turbulence time scales, is introduced. Finally, the energy spectrum and the spectral eddy viscosity are deduced.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198227 , NAS 1.26:198227 , ICASE-95-72 , NIPS-95-06405
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  • 121
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    Flow simulations about steady-complex and unsteady moving configurations using structured-overlapped and unstructured grids (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary problems are evaluated. These are namely the structured-overlapped and the unstructured grid schemes. Both methods use a cell centered, finite volume, upwind approach. The structured-overlapped algorithm uses an approximately factored, alternating direction implicit scheme to perform the time integration, whereas, the unstructured algorithm uses an explicit Runge-Kutta method. To examine the accuracy, efficiency, and limitations of each scheme, they are applied to the same steady complex multicomponent configurations and unsteady moving boundary problems. The steady complex cases consist of computing the subsonic flow about a two-dimensional high-lift multielement airfoil and the transonic flow about a three-dimensional wing/pylon/finned store assembly. The unsteady moving boundary problems are a forced pitching oscillation of an airfoil in a transonic freestream and a two-dimensional, subsonic airfoil/store separation sequence. Accuracy was accessed through the comparison of computed and experimentally measured pressure coefficient data on several of the wing/pylon/finned store assembly's components and at numerous angles-of-attack for the pitching airfoil. From this study, it was found that both the structured-overlapped and the unstructured grid schemes yielded flow solutions of comparable accuracy for these simulations. This study also indicated that, overall, the structured-overlapped scheme was slightly more CPU efficient than the unstructured approach.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199781 , NAS 1.26:199781 , NIPS-95-06448
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    On the Nonlinear Evolution of a Stationary Cross-Flow Vortex in a Fully Three-Dimensional Boundary Layer Flow (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: We consider the nonlinear stability of a fully three-dimensional boundary layer flow in an incompressible fluid and derive an equation governing the nonlinear development of a stationary cross-flow vortex. The amplitude equation is a novel integro-differential equation which has spatial derivatives of the amplitude occurring in the kernal function. It is shown that the evolution of the cross-flow vortex is strongly coupled to the properties of an unsteady wall layer which is in fact driven by an unknown slip velocity, proportional to the amplitude of the cross-flow vortex. The work is extended to obtain the corresponding equation for rotating disk flow. A number of special cases are examined and the numerical solution for one of cases, and further analysis, demonstrates the existence of finite-distance as well as focussing type singularities. The numerical solutions also indicate the presence of a new type of nonlinear wave solution for a certain set of parameter values.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198405 , NAS 1.26:198405 , E-9919 , ICOMP-95-16 , NIPS-95-06270
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  • 123
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    Energy transfer in compressible turbulence (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This letter investigates the compressible energy transfer process. We extend a methodology developed originally for incompressible turbulence and use databases from numerical simulations of a weak compressible turbulence based on Eddy-Damped-Quasi-Normal-Markovian (EDQNM) closure. In order to analyze the compressible mode directly, the well known Helmholtz decomposition is used. While the compressible component has very little influence on the solenoidal part, we found that almost all of the compressible turbulence energy is received from its solenoidal counterpart. We focus on the most fundamental building block of the energy transfer process, the triadic interactions. This analysis leads us to conclude that, at low turbulent Mach number, the compressible energy transfer process is dominated by a local radiative transfer (absorption) in both inertial and energy containing ranges.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198216 , NAS 1.26:198216 , ICASE-95-65 , NIPS-95-06127
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  • 124
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    A self-contained, automated methodology for optimal flow control validated for transition delay (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This paper describes a self-contained, automated methodology for flow control along with a validation of the methodology for the problem of boundary layer instability suppression. The objective of control is to match the stress vector along a portion of the boundary to a given vector; instability suppression is achieved by choosing the given vector to be that of a steady base flow, e.g., Blasius boundary layer. Control is effected through the injection or suction of fluid through a single orifice on the boundary. The present approach couples the time-dependent Navier-Stokes system with an adjoint Navier-Stokes system and optimality conditions from which optimal states, i.e., unsteady flow fields, and control, e.g., actuators, may be determined. The results demonstrate that instability suppression can be achieved without any a priori knowledge of the disturbance, which is significant because other control techniques have required some knowledge of the flow unsteadiness such as frequencies, instability type, etc.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198215 , NAS 1.26:198215 , ICASE-95-64 , NIPS-95-06129
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  • 125
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    On absorbing boundary conditions for linearized Euler equations by a perfectly matched layer (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Recently, Berenger introduced a Perfectly Matched Layer (PML) technique for absorbing electromagnetic waves. In the present paper, a perfectly matched layer is proposed for absorbing out-going two-dimensional waves in a uniform mean flow, generated by linearized Euler equations. It is well known that the linearized Euler equations support acoustic waves, which travel with the speed of sound relative to the mean flow, and vorticity and entropy waves, which travel with the mean flow. The PML equations to be used at a region adjacent to the artificial boundary for absorbing these linear waves are defined. Plane waves solutions to the PML equations are developed and wave propagation and absorption properties are given. It is shown that the theoretical reflection coefficients at an interface between the Euler and PML domains are zero, independent of the angle of incidence and frequency of the waves. As such, the present study points out a possible alternative approach for absorbing out-going waves of the Euler equations with little or no reflection in computation. Numerical examples that demonstrate the validity of the proposed PML equations are also presented.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198224 , NAS 1.26:198224 , ICASE-95-70 , NIPS-95-06126
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  • 126
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    The nonlinear evolution of inviscid Goertler vortices in three-dimensional boundary layers (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The nonlinear development of inviscid Gortler vortices in a three-dimensional boundary layer is considered. We do not follow the classical approach of weakly nonlinear stability problems and consider a mode which has just become unstable. Instead we extend the method of Blackaby, Dando, and Hall (1992), which considered the closely related nonlinear development of disturbances in stratified shear flows. The Gortler modes we consider are initially fast growing and we assume, following others, that boundary-layer spreading results in them evolving in a linear fashion until they reach a stage where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. From the work of Blackaby, Dando and Hall (1993) is apparent, given the range of parameters for the Gortler problem, that there are three possible nonlinear integro-differential evolution equations for the disturbance amplitude. These are a cubic due to viscous effects, a cubic which corresponds to the novel mechanism investigated in this previous paper, and a quintic. In this paper we shall concentrate on the two cubic integro-differential equations and in particular, on the one due to the novel mechanism as this will be the first to affect a disturbance. It is found that the consideration of a spatial evolution problem as opposed to temporal (as was considered in Blackaby, Dando, and Hall, 1992) causes a number of significant changes to the evolution equations.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198222 , NAS 1.26:198222 , ICASE-95-68 , NIPS-95-06128
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  • 127
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    Determination of hydrocarbon abundances and the strength of eddy mixing in the stratosphere of Neptune: Analysis of UVS solar occultation lightcurves (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Work on completing our analysis of the Voyager UVS solar occultation data acquired during Neptune encounter is essentially complete, as testified by the attached poster materials. The photochemical modeling addresses the recent revision in branching ratios for radical production in the photolysis of methane at H Lyman alpha implied by the lab measurements of Mordaunt et al. (1993). The software generated in this effort has been useful for checking the degree to which photochemical models addressing other datasets (mainly infrared) are consistent with the UVS data. This work complements the UVS modeling results in that the IR data refer to deeper pressure levels; as regards the modeling of UVS data, the most significant result is the convincing support for the presence of a stagnant lower stratosphere. Evidence for strong dynamical (mixing) transport of minor constituents at shallower pressures is provided by the UVS data analysis.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-199692 , NAS 1.26:199692 , NIPS-95-05894
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  • 128
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    Thermal infrared spectroscopic observations of Mars from the Kuiper Airborne Observatory (KAO): Constraints on past climates and weathering products (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Spectral observations providing evidence for the presence of volatile-bearing minerals on the surface of Mars were obtained in 1988 and 1990 from the KAO. The 1988 data suggest the presence of 1-3 weight percent (wt%) of carbonate/bicarbonate and 10-15 wt% sulfate/bisulfate associated with martian atmospheric dust. Estimates of the optical depths are approximately 0.60 and approximately 0.35 in 1988 and 1990, respectively.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 345-348
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  • 129
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    Non-linear boundary-layer receptivity due to distributed surface roughness (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The process by which a laminar boundary layer internalizes the external disturbances in the form of instability waves is known as boundary-layer receptivity. The objective of the present research was to determine the effect of acoustic excitation on boundary-layer receptivity for a flat plate with distributed variable-amplitude surface roughness through measurements with a hot-wire probe. Tollmien-Schlichting (T-S) mode shapes due to surface-roughness receptivity have also been determined, analyzed, and shown to be in agreement with theory and other experimental work. It has been shown that there is a linear relationship between the surface roughness and receptivity for certain roughness configurations with constant roughness wavelength. In addition, strong nonlinear receptivity effects exist for certain surface roughness configurations over a band where the surface roughness and T-S wavelength are matched. The results from the present experiment follow the trends predicted by theory and other experimental work for linear receptivity. In addition, the results show the existence of nonlinear receptivity effects for certain combinations of surface roughness elements.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199224 , NAS 1.26:199224
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  • 130
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    Large-Amplitude Long-Wave Instability of a Supersonic Shear Layer (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: For sufficiently high Mach numbers, small disturbances on a supersonic vortex sheet are known to grow in amplitude because of slow nonlinear wave steepening. Under the same external conditions, linear theory predicts slow growth of long-wave disturbances to a thin supersonic shear layer. An asymptotic formulation is given here which adds nonzero shear-layer thickness to the weakly nonlinear formulation for a vortex sheet. Spatial evolution is considered, for a spatially periodic disturbance having amplitude of the same order, in Reynolds number, as the shear-layer thickness. A quasi-equilibrium inviscid nonlinear critical layer is found, with effects of diffusion and slow growth appearing through nonsecularity condition. Other limiting cases are also considered, in an attempt to determine a relationship between the vortex-sheet limit and the long-wave limit for a thin shear layer; there appear to be three special limits, corresponding to disturbances of different amplitudes at different locations along the shear layer.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-198401 , ICOMP-95-14 , E-9912 , NAS 1.15:198401
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  • 131
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    Ultraviolet observations of the Saturnian north aurora and polar haze distribution with the HST-FOC (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, reveal the presence of an auroral emission near 80 deg N with a peak brightness of about 150 kR of total H2 emission. The maximum optical depth of the polar haze layer is found to be located approximately 5 deg equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the observed haze optical depth requires an efficiency of aerosol formation of about 6 percent, indicating that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-199241 , NAS 1.26:199241
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  • 132
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    Full-Scale Direct Numerical Simulation of Two- and Three-Dimensional Instabilities and Rivulet Formulation in Heated Falling Films (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A thin film draining on an inclined plate has been studied numerically using finite element method. Three-dimensional governing equations of continuity, momentum and energy with a moving boundary are integrated in an arbitrary Lagrangian Eulerian frame of reference. Kinematic equation is solved to precisely update interface location. Rivulet formation based on instability mechanism has been simulated using full-scale computation. Comparisons with long-wave theory are made to validate the numerical scheme. Detailed analysis of two- and three-dimensional nonlinear wave formation and spontaneous rupture forming rivulets under the influence of combined thermocapillary and surface-wave instabilities is performed.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198403 , E-9917 , NAS 1.26:198403
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  • 133
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    User's Manual for HPTAM: a Two-Dimensional Heat Pipe Transient Analysis Model, Including the Startup from a Frozen State (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This report describes the user's manual for 'HPTAM,' a two-dimensional Heat Pipe Transient Analysis Model. HPTAM is described in detail in the UNM-ISNPS-3-1995 report which accompanies the present manual. The model offers a menu that lists a number of working fluids and wall and wick materials from which the user can choose. HPTAM is capable of simulating the startup of heat pipes from either a fully-thawed or frozen condition of the working fluid in the wick structure. The manual includes instructions for installing and running HPTAM on either a UNIX, MS-DOS or VMS operating system. Samples for input and output files are also provided to help the user with the code.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199552 , NAS 1.26:199552 , UNM-ISNPS-4-1995
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  • 134
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    Liquid metal micro heat pipes for space radiator applications (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Micromachining is a chemical means of etching three-dimensional structures, typically in single-crystalline silicon. These techniques are leading toward what is coming to be referred to as MEMS (micro electro mechanical systems), where in addition to the ordinary two dimensional (planar) microelectronics, it is possible to build three-dimensional micromotors, electrically-actuated microvalves, hydraulic systems, and much more on the same microchip. These techniques become possible because of differential etching rates of various crystallographic planes and materials used for semiconductor microfabrication. The University of Cincinnati group in collaboration with NASA Lewis formed micro heat pipes in silicon by the above techniques. Work is ongoing at a modest level, but several essential bonding and packaging techniques have been recently developed. Currently, we have constructed and filled water/silicon micro heat pipes. Preliminary thermal tests of arrays of 125 micro heat pipes etched in a 1 inch x 1 inch x 250 micron silicon wafer have been completed. These pipes are instrumented with extremely small P-N junctions to measure their effective conductivity and their maximum operating power. A relatively simple one-dimensional model has been developed in order to predict micro heat pipes' operating characteristics. This information can be used to optimize micro heat pipe design with respect to length, hydraulic diameter, and number of pipes. Work is progressing on the fabrication of liquid-metal micro heat pipes. In order to be compatible with liquid metal (sodium or potassium), the inside of the micro heat pipes will be coated with a refractory metal (such as tungsten, molybdenum, or titanium).
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199122 , NAS 1.26:199122
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    A far-wing line shape theory which satisfies the detailed balance principle (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A far-wing theory in which the validity of the detailed balance principle is maintained in each step of the derivation is presented. The role of the total density matrix including the initial correlations is analyzed rigorously. By factoring out the rapidly varying terms in the complex-time development operator in the interaction representation, better approximate expressions can be obtained. As a result, the spectral density can be expressed in terms of the line-coupling functions in which two coupled lines are arranged symmetrically and whose frequency detunings are omega - 1/2(omega(sub ji) + omega (sub j'i'). Using the approximate values omega - omega(sub ji) results in expressions that do not satisfy the detailed balance principle. However, this principle remains satisfied for the symmetrized spectral density in which not only the coupled lines are arranged symmetrically, but also the initial and final states belonging to the same lines are arranged symmetrically as well.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-111075 , NAS 1.15:111075
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  • 136
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    Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in FY92 and continued into FY93, concentrated on the design of such an experiment whose results may be compared with results obtained in other wind-tunnel facilities. At the same time, concurrent work in the Arizona State University (ASU) Unsteady Wind Tunnel would be conducted on the effects of surface roughness. The second part of the work, which was to be initiated in FY94, would have consisted of experiments conducted in both the 11-foot tunnel at NASA-Ames and the ASU Unsteady Wind Tunnel. However, this work was not continued. This report summarizes the experimental design considerations and some preliminary experiments that made up the first part of the work.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199360 , NAS 1.26:199360
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  • 137
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    Low-speed longitudinal aerodynamic characteristics through poststall for 21 novel planform shapes (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: To identify planform characteristics which have promise for a highly maneuverable vehicle, an investigation was conducted in the Langley Subsonic Basic Research Tunnel to determine the low-speed longitudinal aerodynamics of 21 planform geometries. Concepts studied included twin bodies, double wings, cutout wings, and serrated forebodies. The planform models tested were all 1/4-in.-thick flat plates with beveled edges on the lower surface to ensure uniform flow separation at angle of attack. A 1.0-in.-diameter cylindrical metric body with a hemispherical nose was used to house the six-component strain gauge balance for each configuration. Aerodynamic force and moment data were obtained across an angle-of-attack range of 0 to 70 deg with zero sideslip at a free-stream dynamic pressure of 30 psf. Surface flow visualization studies were also conducted on selected configurations using fluorescent minitufts. Results from the investigation indicate that a cutout wing planform can improve lift characteristics; however, cutout size, shape, and position and wing leading-edge sweep will all influence the effectiveness of the cutout configuration. Tests of serrated forebodies identified this concept as an extremely effective means of improving configuration lift characteristics; increases of up to 25 percent in the value of maximum lift coefficient were obtained.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TP-3503 , L-17301 , NAS 1.60:3503
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  • 138
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    Convective and radiative heating for vehicle return from the Moon and Mars (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The aerothermal environment is examined for two vehicle forebodies near the peak heating points of lunar and martian return-to-earth trajectories at several nominal entry velocities. The first vehicle forebody is that of a 70 deg aerobrake for entry into earth orbit; the second, a capsule of Apollo configuration for direct entry into the earth's atmosphere. The configurations and trajectories are considered likely candidates for such missions. Two-temperature, thermochemical nonequilibrium models are used in the flow field analyses. In addition to Park's empirical model for dissociation under conditions of thermal nonequilibrium, the Gordiets kinetic model for the homonuclear dissociation of N2 and O2 is also considered. Temperature and emission profiles indicate nonequilibrium effects in a 2 to 5 cm post shock region. Substantial portions of the shock layer flow appear to be in equilibrium. The shock layer over an aerobrake for return from the moon exhibits the largest extent of nonequilibrium effects of all considered missions. Differences between the Gordiets and Parks kinetic model were generally very small for the lunar return aerobrake case, the greatest difference of 6.1 percent occurring in the radiative heating levels.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-110185 , NAS 1.15:110185
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  • 139
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    A computational fluid dynamics simulation of the hypersonic flight of the Pegasus(TM) vehicle using an artificial viscosity model and a nonlinear filtering method (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The computational fluid dynamics code, PARC3D, is tested to see if its use of non-physical artificial dissipation affects the accuracy of its results. This is accomplished by simulating a shock-laminar boundary layer interaction and several hypersonic flight conditions of the Pegasus(TM) launch vehicle using full artificial dissipation, low artificial dissipation, and the Engquist filter. Before the filter is applied to the PARC3D code, it is validated in one-dimensional and two-dimensional form in a MacCormack scheme against the Riemann and convergent duct problem. For this explicit scheme, the filter shows great improvements in accuracy and computational time as opposed to the nonfiltered solutions. However, for the implicit PARC3D code it is found that the best estimate of the Pegasus experimental heat fluxes and surface pressures is the simulation utilizing low artificial dissipation and no filter. The filter does improve accuracy over the artificially dissipative case but at a computational expense greater than that achieved by the low artificial dissipation case which has no computational time penalty and shows better results. For the shock-boundary layer simulation, the filter does well in terms of accuracy for a strong impingement shock but not as well for weaker shock strengths. Furthermore, for the latter problem the filter reduces the required computational time to convergence by 18.7 percent.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-186033 , H-2071 , NAS 1.26:186033
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    Vortex perturbation dynamics (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198182 , NAS 1.26:198182 , ICASE-95-52
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    Development of multiobjective optimization techniques for sonic boom minimization (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An optimization procedure is developed for the simultaneous improvement of the aerodynamic and sonic boom characteristics of high speed aircraft. From a sonic boom perspective, it is desirable to minimize the first peak in the overpressure signal at a specified distance away from the aircraft. From aerodynamic point of view, the aerodynamic drag coefficient ratio must be minimized while maintaining the lift coefficient at desired level. The optimization procedure is applied to wing-body configurations related to high speed aircraft. The objectives of this current research are: (1) development of a multiobjective optimization procedure for aerospace vehicles with the integration of sonic boom and aerodynamic performance criteria; and (2) development of semi-analytical approach for calculating sonic boom design sensitivities.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-199083 , NAS 1.26:199083
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    Effect of wake structure on blade-vortex interaction phenomena: Acoustic prediction and validation (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110825 , NAS 1.15:110825 , AD-A294477
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    Computational strategies for three-dimensional flow simulations on distributed computer systems (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This research effort is directed towards an examination of issues involved in porting large computational fluid dynamics codes in use within the industry to a distributed computing environment. This effort addresses strategies for implementing the distributed computing in a device independent fashion and load balancing. A flow solver called TEAM presently in use at Lockheed Aeronautical Systems Company was acquired to start this effort. The following tasks were completed: (1) The TEAM code was ported to a number of distributed computing platforms including a cluster of HP workstations located in the School of Aerospace Engineering at Georgia Tech; a cluster of DEC Alpha Workstations in the Graphics visualization lab located at Georgia Tech; a cluster of SGI workstations located at NASA Ames Research Center; and an IBM SP-2 system located at NASA ARC. (2) A number of communication strategies were implemented. Specifically, the manager-worker strategy and the worker-worker strategy were tested. (3) A variety of load balancing strategies were investigated. Specifically, the static load balancing, task queue balancing and the Crutchfield algorithm were coded and evaluated. (4) The classical explicit Runge-Kutta scheme in the TEAM solver was replaced with an LU implicit scheme. And (5) the implicit TEAM-PVM solver was extensively validated through studies of unsteady transonic flow over an F-5 wing, undergoing combined bending and torsional motion. These investigations are documented in extensive detail in the dissertation, 'Computational Strategies for Three-Dimensional Flow Simulations on Distributed Computing Systems', enclosed as an appendix.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NIPS-95-05591 , NASA-CR-199562 , NAS 1.26:199562
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  • 144
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    Floating shock fitting via Lagrangian adaptive meshes (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: In recent work we have formulated a new approach to compressible flow simulation, combining the advantages of shock-fitting and shock-capturing. Using a cell-centered on Roe scheme discretization on unstructured meshes, we warp the mesh while marching to steady state, so that mesh edges align with shocks and other discontinuities. This new algorithm, the Shock-fitting Lagrangian Adaptive Method (SLAM), is, in effect, a reliable shock-capturing algorithm which yields shock-fitted accuracy at convergence.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 127-138
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  • 145
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    Block distributions on the lunar surface: A comparison between measurements obtained from surface and orbital photography (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Among the hazards that must be negotiated by lunar-landing spacecraft are blocks on the surface of the Moon. Unfortunately, few data exist that can be used to evaluate the threat posed by such blocks to landing spacecraft. Perhaps the best information is that obtained from Surveyor photographs, but those data do not extend to the dimensions of the large blocks that would pose the greatest hazards. Block distributions in the vicinities of the Surveyor 1, 3, 6, and 7 sites have been determined from Lunar Orbiter photography and are presented here. Only large (i.e., greater than or equal to 2.5 m) blocks are measurable in these pictures, resulting in a size gap between the Surveyor and Lunar Orbiter distributions. Nevertheless, the orbital data are self-consistent, a claim supported by the similarity in behavior between the subsets of data from the Surveyor 1, 3, and 6 sites and by the good agreement in position (if not slopes) between the data obtained from the Surveyor 3 photography and those derived from the Lunar Orbiter photographs. Confidence in the results is also justified by the well-behaved distribution of large blocks at the surveyor site. Comparisons between the Surveyor distributions and those derived from the orbital photography permit these observations: (1) in all cases but that for Surveyor 3, the density of large blocks is overestimated by extrapolation of the Surveyor-derived trends; (2) the slopes of the Surveyor-derived distributions are consistently lower than those determined for the large blocks; and (3) these apparent disagreements could be mitigated if the overall shapes of the cumulative lunar block populations were nonlinear, allowing for different slopes over different size intervals. The relatively large gaps between the Surveyor-derived and Orbiter-derived data sets, however, do not permit a determination of those shapes.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-TM-104804 , NAS 1.15:104804 , S-782 , NIPS-96-07702
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  • 146
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    Magnetic heat pump flow director (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A fluid flow director is disclosed. The director comprises a handle body and combed-teeth extending from one side of the body. The body can be formed of a clear plastic such as acrylic. The director can be used with heat exchangers such as a magnetic heat pump and can minimize the undesired mixing of fluid flows. The types of heat exchangers can encompass both heat pumps and refrigerators. The director can adjust the fluid flow of liquid or gas along desired flow directions. A method of applying the flow director within a magnetic heat pump application is also disclosed where the comb-teeth portions of the director are inserted into the fluid flow paths of the heat pump.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
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  • 147
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    The role of small missions in planetary and lunar exploration (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The Space Studies Board of the National Research Council charged its Committee on Planetary and Lunar Exploration (COMPLEX) to (1) examine the degree to which small missions, such as those fitting within the constraints of the Discovery program, can achieve priority objectives in the lunar and planetary sciences; (2) determine those characteristics, such as level of risk, flight rate, target mix, university involvement, technology development, management structure and procedures, and so on, that could allow a successful program; (3) assess issues, such as instrument selection, mission operations, data analysis, and data archiving, to ensure the greatest scientific return from a particular mission, given a rapid deployment schedule and a tightly constrained budget; and (4) review past programmatic attempts to establish small planetary science mission lines, including the Planetary Observers and Planetary Explorers, and consider the impact management practices have had on such programs. A series of small missions presents the planetary science community with the opportunity to expand the scope of its activities and to develop the potential and inventiveness of its members in ways not possible within the confines of large, traditional programs. COMPLEX also realized that a program of small planetary missions was, in and of itself, incapable of meeting all of the prime objectives contained in its report 'An Integrated Strategy for the Planetary Sciences: 1995-2010.' Recommendations are provided for the small planetary missions to fulfill their promise.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-199590 , NAS 1:26:199590
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  • 148
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    Center for Modeling of Turbulence and Transition: Research Briefs, 1995 (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This research brief contains the progress reports of the research staff of the Center for Modeling of Turbulence and Transition (CMOTT) from July 1993 to July 1995. It also constitutes a progress report to the Institute of Computational Mechanics in Propulsion located at the Ohio Aerospace Institute and the Lewis Research Center. CMOTT has been in existence for about four years. In the first three years, its main activities were to develop and validate turbulence and combustion models for propulsion systems, in an effort to remove the deficiencies of existing models. Three workshops on computational turbulence modeling were held at LeRC (1991, 1993, 1994). At present, CMOTT is integrating the CMOTT developed/improved models into CFD tools which can be used by the propulsion systems community. This activity has resulted in an increased collaboration with the Lewis CFD researchers.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198408 , NAS 1.26:198408 , E-9932 , ICOMP-95-17 , CMOTT-95-3
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    Two-dimensional mesh embedding for Galerkin B-spline methods (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A number of advantages result from using B-splines as basis functions in a Galerkin method for solving partial differential equations. Among them are arbitrary order of accuracy and high resolution similar to that of compact schemes but without the aliasing error. This work develops another property, namely, the ability to treat semi-structured embedded or zonal meshes for two-dimensional geometries. This can drastically reduce the number of grid points in many applications. Both integer and non-integer refinement ratios are allowed. The report begins by developing an algorithm for choosing basis functions that yield the desired mesh resolution. These functions are suitable products of one-dimensional B-splines. Finally, test cases for linear scalar equations such as the Poisson and advection equation are presented. The scheme is conservative and has uniformly high order of accuracy throughout the domain.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-110361 , A-950083 , NAS 1.15:110361
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    Numerical Studies of Boundary-Layer Receptivity (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Direct numerical simulations (DNS) of the acoustic receptivity process on a semi-infinite flat plate with a modified-super-elliptic (MSE) leading edge are performed. The incompressible Navier-Stokes equations are solved in stream-function/vorticity form in a general curvilinear coordinate system. The steady basic-state solution is found by solving the governing equations using an alternating direction implicit (ADI) procedure which takes advantage of the parallelism present in line-splitting techniques. Time-harmonic oscillations of the farfield velocity are applied as unsteady boundary conditions to the unsteady disturbance equations. An efficient time-harmonic scheme is used to produce the disturbance solutions. Buffer-zone techniques have been applied to eliminate wave reflection from the outflow boundary. The spatial evolution of Tollmien-Schlichting (T-S) waves is analyzed and compared with experiment and theory. The effects of nose-radius, frequency, Reynolds number, angle of attack, and amplitude of the acoustic wave are investigated. This work is being performed in conjunction with the experiments at the Arizona State University Unsteady Wind Tunnel under the direction of Professor William Saric. The simulations are of the same configuration and parameters used in the wind-tunnel experiments.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-111104 , NAS 1.15:111104
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  • 151
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    Relaxation approximation in the theory of shear turbulence (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Leslie's perturbative treatment of the direct interaction approximation for shear turbulence (Modern Developments in the Theory of Turbulence, 1972) is applied to derive a time dependent model for the Reynolds stresses. The stresses are decomposed into tensor components which satisfy coupled linear relaxation equations; the present theory therefore differs from phenomenological Reynolds stress closures in which the time derivatives of the stresses are expressed in terms of the stresses themselves. The theory accounts naturally for the time dependence of the Reynolds normal stress ratios in simple shear flow. The distortion of wavenumber space by the mean shear plays a crucial role in this theory.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198186 , NAS 1.26:198186 , ICASE-95-55
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  • 152
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    Prediction and measurement of blade-vortex interaction loading (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An extensive quantity of airload measurements was obtained for a pressure-instrumented model of the BO-105 main rotor for a large number of higher-harmonic control (HHC) settings at Duits-Nederlandse Wind Tunnel (DNW). The wake geometry, vortex strength, and vortex core size were also measured through a laser light sheet technique and LDV. These results are used to verify the BVI airload prediction methodologies developed by AFDD, DLR, NASA Langley, and ONERA. The comparisons show that an accurate prediction of the blade motion and the wake geometry is the most important aspect of the BVI airload predictions.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110824 , NAS 1.15:110824 , AD-A294468
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    A guide to the use of the pressure disk rotor model as implemented in INS3D-UP (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This is a guide for the use of the pressure disk rotor model that has been placed in the incompressible Navier-Stokes code INS3D-UP. The pressure disk rotor model approximates a helicopter rotor or propeller in a time averaged manner and is intended to simulate the effect of a rotor in forward flight on the fuselage or the effect of a propeller on other aerodynamic components. The model uses a modified actuator disk that allows the pressure jump across the disk to vary with radius and azimuth. The cyclic and collective blade pitch angles needed to achieve a specified thrust coefficient and zero moment about the hub are predicted. The method has been validated with experimentally measured mean induced inflow velocities as well as surface pressures on a generic fuselage. Overset grids, sometimes referred to as Chimera grids, are used to simplify the grid generation process. The pressure disk model is applied to a cylindrical grid which is embedded in the grid or grids used for the rest of the configuration. This document will outline the development of the method, and present input and results for a sample case.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-4692 , NAS 1.26:4692
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    A perspective on computational aerothermodynamics: Current modeling difficulties (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Future hypersonic vehicles are going to be designed largely with computational fluid dynamic methods based on appropriate physical models. The question on how much of this design process can be completed with the present state of computational aerothermodynamics is addressed. Some limitations of current models are discussed. It is shown that much more research is required before it will be possible to accurately design a hypersonic vehicle for all of its flight conditions. The quantities that must be computed accurately so that a minimum weight hypersonic vehicle can be designed are discussed. The use of computational fluid dynamics methods coupled with current thermochemical models in order to compute the quantities under specific flow conditions is considered.
    Schlagwort(e): AERODYNAMICS
    Materialart: ESA, Proceedings of the 2nd European Symposium on Aerothermodynamics for Space Vehicles; p 365-37
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  • 155
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    Mach 10 experimental database of a three-dimensional scramjet inlet flow field (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The present work documents the experimental database of a combined computational and experimental parametric study of the internal aerodynamics of a generic three-dimensional sidewall compression scramjet inlet configuration at Mach 10. A total of 356 channels of pressure data, including static pressure orifices, pitot pressures, and exit flow rakes, along with oil flow and infrared thermography, provided a detailed experimental description of the flow. Mach 10 tests were performed for three geometric contraction ratios (3, 5, and 9), three Reynolds numbers (0.55 x 10(exp 6) per foot, 1.14 x 10(exp 6) per foot, and 2.15 x 10(exp 6) per foot), and three cowl positions (at the throat and two forward positions). For the higher contraction ratios, a large forward separation of the inflow boundary layer was observed, making the high contraction ratio configurations unsuitable for flight operation. A decrease in the freestream unit Reynolds number (Re) of only a factor of 2 led to a similar upstream separation. Although the presence of such large-scale separations leads to the question of whether the inlet is started, the presence of internal oblique swept shock interactions on the sidewalls seems to indicate that at least in the classical sense, the inlet is not unstarted. The laminar inflow boundary layer therefore appears to be very sensitive to increases in contraction ratio (CR) or decreases in Reynolds number; only the CR = 3 configuration with 0.25, and 50 percent cowl at Re = 2.15 x 10(exp 6) per foot operated 'on design'.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-4648 , L-17349 , NAS 1.15:4648
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    Separation characteristics of generic stores from lee side of an inclined flat plate at Mach 6 (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An experimental investigation was conducted to determine the aerodynamic characteristics of a store as it was separated from the lee side of a flat plate inclined at 15 deg to the free-stream flow at Mach 6. Two store models were tested: a cone cylinder and a roof delta. Force and moment data were obtained for both stores as they were moved in 0.5-in. increments away from the flat plate lee-side separated flow region into the free-stream flow while the store angle of attack was held constant at either 0 deg or 15 deg. The results indicate that both stores had adverse separation characteristics (i.e., negative normal force and pitching moment) at an angle of attack of 0 deg, and the cone cylinder had favorable separation characteristics (i.e., positive normal force and pitching moment) at an angle of attack of 15 deg. At an angle of attack of 15 deg, the separation characteristics of the roof delta are indeterminate at small separation distances and favorable at greater separation distances. These characteristics are the result of the local flow inclination relative to the stores as they traversed through the flat plate lee-side flow field. In addition to plotted data, force and moment data are tabulated and schlieren photographs of the stores and flat plate are presented.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-4652 , L-17384 , NAS 1.15:4652
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    A longitudinal aerodynamic data repeatability study for a commercial transport model test in the National Transonic Facility (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A high Reynolds number investigation of a commercial transport model was conducted in the National Transonic Facility (NTF) at Langley Research Center. This investigation was part of a cooperative effort to test a 0.03-scale model of a Boeing 767 airplane in the NTF over a Mach number range of 0.70 to 0.86 and a Reynolds number range of 2.38 to 40.0 x 10(exp 6) based on the mean aerodynamic chord. One of several specific objectives of the current investigation was to evaluate the level of data repeatability attainable in the NTF. Data repeatability studies were performed at a Mach number of 0.80 with Reynolds numbers of 2.38, 4.45, and 40.0 x 10(exp 6) and also at a Mach number of 0.70 with a Reynolds number of 40.0 x 10(exp 6). Many test procedures and data corrections are addressed in this report, but the data presented do not include corrections for wall interference, model support interference, or model aeroelastic effects. Application of corrections for these three effects would not affect the results of this study because the corrections are systematic in nature and are more appropriately classified as sources of bias error. The repeatability of the longitudinal stability-axis force and moment data has been accessed. Coefficients of lift, drag, and pitching moment are shown to repeat well within the pretest goals of plus or minus 0.005, plus or minus 0.0001, and plus or minus 0.001, respectively, at a 95-percent confidence level over both short- and near-term periods.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TP-3522 , L-17412 , NAS 1.60:3522
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    Asteroid entry in Venusian atmosphere: Pressure and density fields effect on crater formation (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The objectives are to look at time scales of overpressure compared to cratering and to determine: what are the transient pressure and density due to atmospheric entry; do shock waves evacuate ambient gas; do transient atmospheric disturbances 'settle down' during cratering; can the pressure/density field be approximated as quasi-static; how does disturbance scale with impactor size; and what is the role of atmospheric thickness. The general approach is to perform inexpensive exploratory calculations, perform experiments to validate code and observe crater growth, and to follow up with more realistic coupling calculations. This viewgraph presentation presents progress made with the objective to obtain useful scaling relationships for crater formation when atmospheric effects are important.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-199155 , NAS 1.26:199155
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    Numerical thermal analyses of heat exchangers for the stirling engine application (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The Regenerator, Cooler and Heater for the NASA Space Power Research Engine (SPRE) have been analyzed in detail for laminar, incompressible and oscillatory flow conditions. Each component has been analyzed independently and in detail with the regenerator being modeled as two-parallel-plates channel with a solid wall. The ends of the channel are exposed to two reservoir maintained at different temperature thus providing an axial temperature gradient along the channel. The cooler and heater components have been modeled as circular pipes with isothermal walls. Two different types of thermal boundary conditions have been investigated for the cooler and heater, namely, symmetric and asymmetric temperature inflow. In symmetric temperature inflow the flow enters the channel with the same temperature in throughout the velocity cycle whereas, in asymmetric temperature inflow the flow enters with a different temperature in each half cycle. The study was conducted over a wide range of Maximum Reynolds number (RE(max) varying from 75 to 60000, Valensi number (Va) from 2.5 to 800, and relative amplitude of fluid displacement (A(sub r) from 0.357 to 1.34. A two dimensional Finite volume method based on the SIMPLE algorithm was used to solve the governing partial differential equations. Post processing programs were developed to effectively describe the heat transfer mechanism under oscillatory flows. The computer code was validated by comparing with existing analytical solutions for oscillating flows. The thermal field have been studied with the help of temperature contour and three dimensional plots. The instantaneous friction factor, wall heat flux and heat transfer coefficient have been examined. It has been concluded that in general, the frictional factor and heat transfer coefficient are higher under oscillatory flow conditions when the Valensi number is high. Also, the thermal efficiency decreases for lower A(r) values. Further, the usual steady state definition for the heat transfer coefficient does not seem to be valid.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199120 , NAS 1.26:199120
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    Drag measurements of an axisymmetric nacelle mounted on a flat plate at supersonic speeds (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An experimental investigation was conducted to determine the effect of diverter wedge half-angle and nacelle lip height on the drag characteristics of an assembly consisting of a nacelle fore cowl from a typical high-speed civil transport (HSCT) and a diverter mounted on a flat plate. Data were obtained for diverter wedge half-angles of 4.0 deg, 6.0 deg, and 8.0 deg and ratios of the nacelle lip height above a flat plate to the boundary-layer thickness (h(sub n)/delta) of approximately 0.87 to 2.45. Limited drag data were also obtained on a complete nacelle/diverter configuration that included fore and aft cowls. Although the nacelle/diverter drag data were not corrected for base pressures or internal flow drag, the data are useful for comparing the relative drag of the configuration tested. The tests were conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.50, 1.80, 2.10, and 2.40 and Reynolds numbers ranging from 2.00 x 10(exp 6) to 5.00 x 10(exp 6) per foot. The results of this investigation showed that the nacelle/diverter drag essentially increased linearly with increasing h(sub n)/delta except near 1.0 where the data showed a nonlinear behavior. This nonlinear behavior was probably caused by the interaction of the shock waves from the nacelle/diverter configuration with the flat-plate boundary layer. At the lowest h(sub n)/delta tested, the diverter wedge half-angle had virtually no effect on the nacelle/diverter drag. However, as h(sub n)/delta increased, the nacelle/diverter drag increased as diverter wedge half-angle increased.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-4660 , L-17416 , NAS 1.15:4660
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    Investigation of water droplet trajectories within the NASA icing research tunnel (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: Water droplet trajectories within the NASA Lewis Research Center's Icing Research Tunnel (IRT) were studied through computer analysis. Of interest was the influence of the wind tunnel contraction and wind tunnel model blockage on the water droplet trajectories. The computer analysis was carried out with a program package consisting of a three-dimensional potential panel code and a three-dimensional droplet trajectory code. The wind tunnel contraction was found to influence the droplet size distribution and liquid water content distribution across the test section from that at the inlet. The wind tunnel walls were found to have negligible influence upon the impingement of water droplets upon a wing model.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-107023 , E-9828 , NAS 1.15:107023
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    SOFIA 2 model telescope wind tunnel test report (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This document outlines the tests performed to make aerodynamic force and torque measurements on the SOFIA wind tunnel model telescope. These tests were performed during the SOFIA 2 wind tunnel test in the 14 ft wind tunnel during the months of June through August 1994. The test was designed to measure the dynamic cross elevation moment acting on the SOFIA model telescope due to aerodynamic loading. The measurements were taken with the telescope mounted in an open cavity in the tail section of the SOFIA model 747. The purpose of the test was to obtain an estimate of the full scale aerodynamic disturbance spectrum, by scaling up the wind tunnel results (taking into account differences in sail area, air density, cavity dimension, etc.). An estimate of the full scale cross elevation moment spectrum was needed to help determine the impact this disturbance would have on the telescope positioning system requirements. A model of the telescope structure, made of a light weight composite material, was mounted in the open cavity of the SOFIA wind tunnel model. This model was mounted via a force balance to the cavity bulkhead. Despite efforts to use a 'stiff' balance, and a lightweight model, the balance/telescope system had a very low resonant frequency (37 Hz) compared to the desired measurement bandwidth (1000 Hz). Due to this mechanical resonance of the balance/telescope system, the balance alone could not provide an accurate measure of applied aerodynamic force at the high frequencies desired. A method of measurement was developed that incorporated accelerometers in addition to the balance signal, to calculate the aerodynamic force.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110668 , SER-PK-001 , NAS 1.15:110668
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    Parallel adaptive mesh refinement within the PUMAA3D Project (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: To enable the solution of large-scale applications on distributed memory architectures, we are designing and implementing parallel algorithms for the fundamental tasks of unstructured mesh computation. In this paper, we discuss efficient algorithms developed for two of these tasks: parallel adaptive mesh refinement and mesh partitioning. The algorithms are discussed in the context of two-dimensional finite element solution on triangular meshes, but are suitable for use with a variety of element types and with h- or p-refinement. Results demonstrating the scalability and efficiency of the refinement algorithm and the quality of the mesh partitioning are presented for several test problems on the Intel DELTA.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 163-170
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  • 164
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    Some observations on mesh refinement schemes applied to shock wave phenomena (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: This workshop's double-wedge test problem is taken from one of a sequence of experiments which were performed in order to classify the various canonical interactions between a planar shock wave and a double wedge. Therefore to build up a reasonably broad picture of the performance of our mesh refinement algorithm we have simulated three of these experiments and not just the workshop case. Here, using the results from these simulations together with their experimental counterparts, we make some general observations concerning the development of mesh refinement schemes for shock wave phenomena.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 79-93
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  • 165
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    Thermocapillary flow with evaporation and condensation at low gravity. Part 2: Deformable surface (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The free surface behavior of a volatile wetting liquid at low gravity is studied using scaling and numerical techniques. An open cavity model, which was applied in part 1 to investigate fluid flow and heat transfer in non-deforming pores, is used to evaluate the influence of convection on surface morphology with length scales and subcooling/superheating limits of 1 less than or equal to D less than or equal to 10(exp 2) microns and approximately 1 K, respectively. Results show that the menisci shapes of highly wetting fluids are sensitive to thermocapillary flow and to a lesser extent the recoil force associated with evaporation and condensation. With subcooling, thermocapillarity produces a suction about the pore centerline that promotes loss of mechanical equilibrium, while condensation exerts an opposing force that under some conditions offsets this destabilizing influence. With superheating, thermocapillarity and evaporation act in the same direction and mutually foster surface stability. All of these trends are magnified by high capillary and Biot numbers, and the stronger circulation intensities associated with small contact angles. These phenomena strongly depend on the thermal and interfacial equilibrium between the liquid and vapor, and have important ramifications for systems designed to maintain a pressure differential across a porous surface.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-111221 , NAS 1.15:111221 , NIPS-96-07300
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  • 166
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    Methods for prismatic/tetrahedral grid generation and adaptation (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 201-210
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  • 167
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    An adaptive remeshing scheme for vortex dominated flows using three-dimensional unstructured grids (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: An adaptive remeshing procedure for vortex dominated flows is described, which uses three-dimensional unstructured grids. Surface grid adaptation is achieved using the static pressure as an adaptation parameter, while entropy is used in the field to accurately identify high vorticity regions. An emphasis has been placed in making the scheme as automatic as possible so that a minimum user interaction is required between remeshing cycles. Adapted flow solutions are obtained on two sharp-edged configurations at low speed, high angle-of-attack flow conditions. The results thus obtained are compared with fine grid CFD solutions and experimental data, and conclusions are drawn as to the efficiency of the adaptive procedure.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 211-217
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  • 168
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    Adaptively-refined overlapping grids for the numerical solution of systems of hyperbolic conservation laws (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Adaptive mesh refinement (AMR) in conjunction with higher-order upwind finite-difference methods have been used effectively on a variety of problems in two and three dimensions. In this paper we introduce an approach for resolving problems that involve complex geometries in which resolution of boundary geometry is important. The complex geometry is represented by using the method of overlapping grids, while local resolution is obtained by refining each component grid with the AMR algorithm, appropriately generalized for this situation. The CMPGRD algorithm introduced by Chesshire and Henshaw is used to automatically generate the overlapping grid structure for the underlying mesh.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 95-110
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  • 169
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    Effect of baffle on slosh reaction forces in rotating liquid helium subjected to a lateral impulse in microgravity (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Sloshing dynamics within a partially filled rotating Dewar of superfluid He II are investigated in response to a lateral impulse. The study investigates several factors, including how the rotating bubble of superfluid He II reacts to the impulse in microgravity, how the amplitudes of slosh reaction forces act on the Dewar with various rotating speeds, how the frequencies of the sloshing modes excited differ in terms of differences in rotating speeds, and how the sloshing dynamics differ with and without a baffle. The numerical computation of sloshing dynamics is based on the noninertial frame spacecraft-bound coordinates. Results of the simulations are illustrated.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-200034 , NAS 1.26:200034 , NIPS-96-07279
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  • 170
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    Completing the Copernican Revolution: The search for other planetary systems (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The past few decades have witnessed significant advances in our understanding of how stars form, and there has been an associated increase in our knowledge of conditions and phenomena in the early solar system. These have led to the formulation of a paradigm for the origin of the solar system that is sufficiently complete that its basic elements can be tested directly through observations. A simple, but profound, consequence of the paradigm is that most if not all stars should be accompanied by planetary systems. The accuracy of instruments that can be used in such searches has improved to the point that Jupiter-like companions to a number of nearby stars could be detected. However, the results to date are that no other planetary systems have been detected, and the absence of detection is becoming statistically significant, particularly as it relates to the existence of brown dwarf companions to main-sequence stars.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA-CR-200033 , NAS 1.26:200033 , NIPS-96-07278
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  • 171
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    A two dimensional interface element for coupling of independently modeled three dimensional finite element meshes and extensions to dynamic and non-linear regimes (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The work reported here pertains only to the first year of research for a three year proposal period. As a prelude to this two dimensional interface element, the one dimensional element was tested and errors were discovered in the code for built-up structures and curved interfaces. These errors were corrected and the benchmark Boeing composite crown panel was analyzed successfully. A study of various splines led to the conclusion that cubic B-splines best suit this interface element application. A least squares approach combined with cubic B-splines was constructed to make a smooth function from the noisy data obtained with random error in the coordinate data points of the Boeing crown panel analysis. Preliminary investigations for the formulation of discontinuous 2-D shell and 3-D solid elements were conducted.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-199951 , NAS 1.26:199951 , NIPS-96-07072
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  • 172
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    Zero side force volute development (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Collector scrolls on high performance centrifugal pumps are currently designed with methods which are based on very approximate flowfield models. Such design practices result in some volute configurations causing excessive side loads even at design flowrates. The purpose of this study was to develop and verify computational design tools which may be used to optimize volute configurations with respect to avoiding excessive loads on the bearings. The new design methodology consisted of a volute grid generation module and a computational fluid dynamics (CFD) module to describe the volute geometry and predict the radial forces for a given flow condition, respectively. Initially, the CFD module was used to predict the impeller and the volute flowfields simultaneously; however, the required computation time was found to be excessive for parametric design studies. A second computational procedure was developed which utilized an analytical impeller flowfield model and an ordinary differential equation to describe the impeller/volute coupling obtained from the literature, Adkins & Brennen (1988). The second procedure resulted in 20 to 30 fold increase in computational speed for an analysis. The volute design analysis was validated by postulating a volute geometry, constructing a volute to this configuration, and measuring the steady radial forces over a range of flow coefficients. Excellent agreement between model predictions and observed pump operation prove the computational impeller/volute pump model to be a valuable design tool. Further applications are recommended to fully establish the benefits of this new methodology.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199198 , NAS 1.26:199198 , SECA-FR-95-08 , NIPS-95-06847
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  • 173
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    Polymer/riblet combination for hydrodynamic skin friction reduction (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A process is disclosed for reducing skin friction and inhibiting the effects of liquid turbulence in a system involving the flow of a liquid along the surface of a body, e.g. a marine vehicle. This process includes injecting a drag reducing polymer into the valleys of adjacent, evenly spaced, longitudinal grooves extending along the length of the surface of the body, so that the rate of diffusion of the polymer from individual grooves into the liquid flow is predictably controlled by the groove dimensions. When the polymer has diffused over the tips of the grooves into the near wall region of the boundary layer, the polymer effectively reduces the turbulent skin friction. A substantial drag reducing effect is achieved with less polymer than must be used to lower skin friction when the surface of the body is smooth.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
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  • 174
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    Flight test evaluation of the E-systems Differential GPS category 3 automatic landing system (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Test flights were conducted to evaluate the capability of Differential Global Positioning System (DGPS) to provide the accuracy and integrity required for International Civil Aviation Organization (ICAO) Category (CAT) III precision approach and landings. These test flights were part of a Federal Aviation Administration (FAA) program to evaluate the technical feasibility of using DGPS based technology for CAT III precision approach and landing applications. An IAI Westwind 1124 aircraft (N24RH) was equipped with DGPS receiving equipment and additional computing capability provided by E-Systems. The test flights were conducted at NASA Ames Research Center's Crows Landing Flight Facility, Crows Landing, California. The flight test evaluation was based on completing 100 approaches and landings. The navigation sensor error accuracy requirements were based on ICAO requirements for the Microwave Landing System (MLS). All of the approaches and landings were evaluated against ground truth reference data provided by a laser tracker. Analysis of these approaches and landings shows that the E-Systems DGPS system met the navigation sensor error requirements for a successful approach and landing 98 out of 100 approaches and landings, based on the requirements specified in the FAA CAT III Level 2 Flight Test Plan. In addition, the E-Systems DGPS system met the integrity requirements for a successful approach and landing or stationary trial for all 100 approaches and landings and all ten stationary trials, based on the requirements specified in the FAA CAT III Level 2 Flight Test Plan.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110368 , NAS 1.15:110368 , A-950096
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  • 175
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    Tables of properties of airfoil polynomials (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This monograph provides an extensive list of formulas for airfoil polynomials. These polynomials provide convenient expansion functions for the description of the downwash and pressure distributions of linear theory for airfoils in both steady and unsteady subsonic flow.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-RP-1343 , L-17420 , NAS 1.61:1343
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  • 176
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    HPTAM, a two-dimensional Heat Pipe Transient Analysis Model, including the startup from a frozen state (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A two-dimensional Heat Pipe Transient Analysis Model, 'HPTAM,' was developed to simulate the transient operation of fully-thawed heat pipes and the startup of heat pipes from a frozen state. The model incorporates: (a) sublimation and resolidification of working fluid; (b) melting and freezing of the working fluid in the porous wick; (c) evaporation of thawed working fluid and condensation as a thin liquid film on a frozen substrate; (d) free-molecule, transition, and continuum vapor flow regimes, using the Dusty Gas Model; (e) liquid flow and heat transfer in the porous wick; and (f) thermal and hydrodynamic couplings of phases at their respective interfaces. HPTAM predicts the radius of curvature of the liquid meniscus at the liquid-vapor interface and the radial location of the working fluid level (liquid or solid) in the wick. It also includes the transverse momentum jump condition (capillary relationship of Pascal) at the liquid-vapor interface and geometrically relates the radius of curvature of the liquid meniscus to the volume fraction of vapor in the wick. The present model predicts the capillary limit and partial liquid recess (dryout) in the evaporator wick, and incorporates a liquid pooling submodel, which simulates accumulation of the excess liquid in the vapor core at the condenser end.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199553 , NAS 1.26:199553 , UNM-ISNPS-4-1995
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  • 177
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    Low-speed wind-tunnel investigation of a porous forebody and nose strakes for yaw control of a multirole fighter aircraft (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Low-speed wind-tunnel tests were conducted in the Langley 12-Foot Low-Speed Tunnel on a model of the Boeing Multirole Fighter (BMRF) aircraft. This single-seat, single-engine configuration was intended to be an F-16 replacement that would incorporate many of the design goals and advanced technologies of the F-22. Its mission requirements included supersonic cruise without afterburner, reduced observability, and the ability to attack both air-to-air and air-to-ground targets. So that it would be effective in all phases of air combat, the ability to maneuver at angles of attack up to and beyond maximum lift was also desired. Traditional aerodynamic yaw controls, such as rudders, are typically ineffective at these higher angles of attack because they are usually located in the wake from the wings and fuselage. For this reason, this study focused on investigating forebody-mounted controls that produces yawing moments by modifying the strong vortex flowfield being shed from the forebody at high angles of attack. Two forebody strakes were tested that varied in planform and chordwise location. Various patterns of porosity in the forebody skin were also tested that differed in their radial coverage and chordwise location. The tests were performed at a dynamic pressure of 4 lb/ft(exp 2) over an angle-of-attack range of -4 deg to 72 deg and a sideslip range of -10 deg to 10 deg. Static force data, static pressures on the surface of the forebody, and videotapes of flow-visualization using laser-illuminated smoke were obtained.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-4685 , NAS 1.26:4685
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  • 178
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    Vortex wakes of rotorcraft (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This paper presents an overview of the complex unsteady vortical flows that comprise the wakes of rotary-wing aircraft; of the effects these tangled vortical structures have on the performance, noise, and vibration; and of some of the recent attempts to measure, predict, and control the phenomena. The main points are illustrated with a number of examples from the recent literature and technical conferences.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110822 , NAS 1.15:110822 , AD-A294465
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  • 179
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    Pressure Distributions from Subsonic Tests of a NACA 0012 Semispan Wing Model (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: An unswept, semispan wing model incorporating a NACA 0012 airfoil section was tested in the Langley 14- by 22-Foot Subsonic Tunnel. This report contains pressure data which document effects of wing configuration and free-stream conditions on wing pressure distributions. The untwisted wing incorporated a full-span, leading-edge Krueger flap and a full-span, single-slotted trailing-edge flap. The trailing-edge flap was tested at a deflection angle of 40 degrees and the Krueger flap at a deflection of 55 degrees. Three wing configurations were tested: cruise, trailing-edge flap only, and Knueger flap and trailing-edge flap deployed. Tests were conducted at free-stream dynamic pressures of 15, 30 and 60 psf, with corresponding chord Reynolds numbers of 1.22 to 2.11 million and Mach numbers of 0.12 to 0.20. Angles of attack presented range from 0 to 20 degrees, depending on wing configuration. The data are presented without analysis.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110148 , NAS 1.15:110148
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  • 180
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    Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-111064 , NAS 1.15:111064
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  • 181
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    Multidisciplinary design optimization using multiobjective formulation techniques (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: This report addresses the development of a multidisciplinary optimization procedure using an efficient semi-analytical sensitivity analysis technique and multilevel decomposition for the design of aerospace vehicles. A semi-analytical sensitivity analysis procedure is developed for calculating computational grid sensitivities and aerodynamic design sensitivities. Accuracy and efficiency of the sensitivity analysis procedure is established through comparison of the results with those obtained using a finite difference technique. The developed sensitivity analysis technique are then used within a multidisciplinary optimization procedure for designing aerospace vehicles. The optimization problem, with the integration of aerodynamics and structures, is decomposed into two levels. Optimization is performed for improved aerodynamic performance at the first level and improved structural performance at the second level. Aerodynamic analysis is performed by solving the three-dimensional parabolized Navier Stokes equations. A nonlinear programming technique and an approximate analysis procedure are used for optimization. The proceduredeveloped is applied to design the wing of a high speed aircraft. Results obtained show significant improvements in the aircraft aerodynamic and structural performance when compared to a reference or baseline configuration. The use of the semi-analytical sensitivity technique provides significant computational savings.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-199290 , NAS 1.26:199290
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  • 182
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    Weakly nonparallel and curvature effects on stationary crossflow instability: Comparison of results from multiple-scales analysis and parabolized stability equations (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A multiple-scales approach is used to approximate the effects of nonparallelism and streamwise surface curvature on the growth of stationary crossflow vortices in incompressible, three-dimesional boundary layers. The results agree with results predicted by solving the parabolized stability equations in regions where the nonparallelism is sufficiently weak. As the nonparallelism increases, the agreement between the two approaches worsens. An attempt has been made to quantify the nonparallelism on flow stability in terms of a nondimensional number that describes the rate of change of the mean flow relative to the disturbance wavelength. We find that the above nondimensional number provides useful information about the adequacy of the multiple-scales approximation for different disturbances for a given flow geometry, but the number does not collapse data for different flow geometries onto a single curve.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198200 , NAS 1.26:198200
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  • 183
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    Delta wing vortex manipulation using pulsed and steady blowing during ramp pitching (1995)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: The effectiveness of steady and pulsed blowing as a method of controlling delta wing vortices during ramp pitching has been investigated in flow visualization experiments conducted in a water tunnel. The recessed angled spanwise blowing technique was utilized for vortex manipulation. This technique was implemented on a beveled 60 delta wing using a pair of blowing ports located beneath the vortex core at 40% chord. The flow was injected primarily in the spanwise direction but was also composed of a component normal to the wing surface. The location of vortex burst was measured as a function of blowing intensity and pulsing frequency under static conditions, and the optimum blowing case was applied at three different wing pitching rates. Experimental results have shown that, when the burst location is upstream of the blowing port, pulsed blowing delays vortex breakdown in static and dynamic cases. Dynamic tests verified the existence of a hysteresis effect and demonstrated the improvements offered by pulsed blowing over both steady blowing and no-blowing scenarios. The application of blowing, at the optimum pulsing frequency, made the vortex breakdown location comparable in static and ramp pitch-up conditions.
    Schlagwort(e): AERODYNAMICS
    Materialart: NIPS-95-05494 , NASA-CR-199624 , NAS 1.26:199624 , AIAA PAPER 95-1817-CP , United States
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  • 184
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    Flow characteristics in boundary layer bleed slots with plenum (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Numerical simulations were conducted to investigate the performance characteristics of bleed through normal slots and its effect on the turbulent boundary layer development under zero and strong adverse pressure gradient caused by incident oblique shock. The solution to the compressible Navier-Stokes and k-epsilon equations was obtained in a domain that includes the regions inside the bleed slot and plenum in addition to the external flow. The computational results demonstrate the interactions between the plenum and bleed flow and the effect of incident shock on the boundary layer development downstream. The computed results agree with the experimentally measured pitot and static pressure distribution inside the slot. The bleed mass flow without incident shock was underpredicted over the range of plenum pressures. The computations predicted the measured increase in bleed mass flow with incident shock.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-199637 , NIPS-95-05580 , NAS 1.26:199637 , AIAA PAPER 95-0033
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  • 185
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    The 3-D wake measurements near a hovering rotor for determining profile and induced drag (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile-and-induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter (LV) measurements on the vortex core and to assess the extent of the positional mandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TP-3577 , A-950078 , NAS 1.60:3577 , ATCOM-TR-95-A-006
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  • 186
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    Numerical simulation of supersonic and hypersonic inlet flow fields (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: This report summarizes the research performed by North Carolina State University and NASA Ames Research Center under Cooperative Agreement NCA2-719, 'Numerical Simulation of Supersonic and Hypersonic Inlet Flow Fields". Four distinct rotated upwind schemes were developed and investigated to determine accuracy and practicality. The scheme found to have the best combination of attributes, including reduction to grid alignment with no rotation, was the cell centered non-orthogonal (CCNO) scheme. In 2D, the CCNO scheme improved rotation when flux interpolation was extended to second order. In 3D, improvements were less dramatic in all cases, with second order flux interpolation showing the least improvement over grid aligned upwinding. The reduction in improvement is attributed to uncertainty in determining optimum rotation angle and difficulty in performing accurate and efficient interpolation of the angle in 3D. The CCNO rotational technique will prove very useful for increasing accuracy when second order interpolation is not appropriate and will materially improve inlet flow solutions.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-CR-199428 , NAS 1.26:199428
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  • 187
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    Adaptively Refined Euler and Navier-Stokes Solutions with a Cartesian-Cell Based Scheme (1995)
    In:  CASI
    Details
    Publikationsdatum: 2014-10-15
    Beschreibung: A Cartesian-cell based scheme with adaptive mesh refinement for solving the Euler and Navier-Stokes equations in two dimensions has been developed and tested. Grids about geometrically complicated bodies were generated automatically, by recursive subdivision of a single Cartesian cell encompassing the entire flow domain. Where the resulting cells intersect bodies, N-sided 'cut' cells were created using polygon-clipping algorithms. The grid was stored in a binary-tree data structure which provided a natural means of obtaining cell-to-cell connectivity and of carrying out solution-adaptive mesh refinement. The Euler and Navier-Stokes equations were solved on the resulting grids using an upwind, finite-volume formulation. The inviscid fluxes were found in an upwinded manner using a linear reconstruction of the cell primitives, providing the input states to an approximate Riemann solver. The viscous fluxes were formed using a Green-Gauss type of reconstruction upon a co-volume surrounding the cell interface. Data at the vertices of this co-volume were found in a linearly K-exact manner, which ensured linear K-exactness of the gradients. Adaptively-refined solutions for the inviscid flow about a four-element airfoil (test case 3) were compared to theory. Laminar, adaptively-refined solutions were compared to accepted computational, experimental and theoretical results.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Langley Research Center, ICASE(LaRC Workshop on Adaptive Grid Methods; p 153-161
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  • 188
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    Design, construction and testing of annular diffusers for high speed civil transportation combustor applications (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: A theoretical and an experimental design study of subsonic flow through curved-wall annular diffusers is being carried out in order to establish the most pertinent design parameters for such devices and the implications of their application in the design of engine components in the aerospace industries. This investigation consists of solving numerically the full Navier Stokes and Continuity equations for the time-mean flow. Various models of turbulence are being evaluated for adoption throughout the study and comparisons would be made with experimental data where they exist. Assessment of diffuser performance based on the dissipated mechanical energy would also be made. The experimental work involves the application of Computer Aided Design software tool to the development of a suitable annular diffuser geometry and the subsequent downloading of such data to a CNC machine at Central State University. The results of the investigations are expected to indicate that more cost effective component design of such devices as effective component design of such devices as diffusers which normally contain complex flows can still be achieved. In this regard a review paper was accepted and presented at the First International Conference on High Speed Civil Transportation Research held at North Carolina A&T in December of 1994.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Lewis Reserch Center, HBCUs Research Conference Agenda and Abstracts; p 13
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  • 189
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    A phenomenological treatment of rotating turbulence (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The strong similarity between the magnetohydrodynamic (MHD) turbulence and initially isotropic turbulence subject to rotation is noted. We then apply the MHD phenomenologies of Kraichnan and Matthaeus & Zhou to rotating turbulence. When the turbulence is subject to a strong rotation, the energy spectrum is found to scale as E(k) = C(sub Omega)(Omega(sub epsilon))(sup 1/2)k(sup -2), where Omega is the rotation rate, k is the wavenumber, and epsilon is the dissipation rate. This spectral form is consistent with a recent letter by Zeman. However, here the constant C(sub Omega) is found to be related to the Kolmogorov constant and is estimated in the range 1.22 - 1.87 for the typical values of the latter constant. A 'rule' that relates spectral transfer times to the eddy turnover time and the time scale for decay of the triple correlations is deduced. A hypothesis for the triple correlation decay rate leads to the spectral law which varies between the '-5/3' (without rotation) and '-2' laws (with strong rotation). For intermediate rotation rates, the spectrum varies according to the value of a dimensionless parameter that measures the strength of the rotation wavenumber k(sub Omega) = (Omega(sup 3)/epsiolon)(sup 1/2) relative to the wavenumber k. An eddy viscosity is derived with an explicit dependence on the rotation rate.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198168 , NAS 1.26:198168 , ICASE-95-43
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  • 190
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    Aeroelastic stability of wind turbine blade/aileron systems (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Aeroelastic stability analyses have been performed for the MOD-5A blade/aileron system. Various configurations having different aileron torsional stiffness, mass unbalance, and control system damping have been investigated. The analysis was conducted using a code recently developed by the General Electric Company - AILSTAB. The code extracts eigenvalues for a three degree of freedom system, consisting of: (1) a blade flapwise mode; (2) a blade torsional mode; and (3) an aileron torsional mode. Mode shapes are supplied as input and the aileron can be specified over an arbitrary length of the blade span. Quasi-steady aerodynamic strip theory is used to compute aerodynamic derivatives of the wing-aileron combination as a function of spanwise position. Equations of motion are summarized herein. The program provides rotating blade stability boundaries for torsional divergence, classical flutter (bending/torsion) and wing/aileron flutter. It has been checked out against fixed-wing results published by Theodorsen and Garrick. The MOD-5A system is stable with respect to divergence and classical flutter for all practical rotor speeds. Aileron torsional stiffness must exceed a minimum critical value to prevent aileron flutter. The nominal control system stiffness greatly exceeds this minimum during normal operation. The basic system, however, is unstable for the case of a free (or floating) aileron. The instability can be removed either by the addition of torsional damping or mass-balancing the ailerons. The MOD-5A design was performed by the General Electric Company, Advanced Energy Program Department under Contract DEN3-153 with NASA Lewis Research Center and sponsored by the Department of Energy.
    Schlagwort(e): AERODYNAMICS
    Materialart: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 99-114
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  • 191
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    A numerical method for solving the three-dimensional parabolized Navier-Stokes equations (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A numerical technique that solves the parabolized form of the Navier-Stokes equations is presented. Such a method makes it possible to obtain very detailed descriptions of the flowfield in a relatively modest CPU time. The present approach is based on a space-marching technique, uses a finite volume discretization and an upwind flux-difference splitting scheme for the evaluation of the inviscid fluxes. Second order accuracy is achieved following the guidelines of the the ENO schemes. The methodology is used to investigate three-dimensional supersonic viscous flows over symmetric corners. Primary and secondary streamwise vortical structures embedded in the boundary layer and originated by the interaction with shock waves are detected and studied. For purpose of validation, results are compared with experimental data extracted from literature. The agreement is found to be satisfactory. In conclusion, the numerical method proposed seems to be promising as it permits, at a reasonable computational expense, investigation of complex three-dimensional flowfields in great detail.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198159 , NAS 1.26:198159 , ICASE-95-38
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  • 192
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    On the modulational instability of large amplitude waves in supersonic boundary layers (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The evolution of large amplitude Tollmien-Schlichting waves in a supersonic boundary layer is investigated. Disturbances which have their wavenumber and frequency slowly varying in time and space are described using a phase equation type of approach. Unlike the incompressible case we find that the initial bifurcation to a finite amplitude Tollmien-Schlichting wave is subcritical for most Mach numbers. In fact the bifurcation is only supercritical for a small range of Mach numbers and even then for only a finite range of wave propagation angles. The modulational instability of large amplitude wavetrains is considered and is shown to be governed by an equation similar to Burgers equation but with the viscous term replaced by a fractional derivative. A numerical investigation of the solution of this equation is described. It is shown that uniform wavetrains are unstable.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-195072 , NAS 1.26:195072 , ICASE-95-29
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  • 193
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    Calculation of three-dimensional (3-D) internal flow by means of the velocity-vorticity formulation on a staggered grid (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A method has been developed to accurately compute the viscous flow in three-dimensional (3-D) enclosures. This method is the 3-D extension of a two-dimensional (2-D) method developed for the calculation of flow over airfoils. The 2-D method has been tested extensively and has been shown to accurately reproduce experimental results. As in the 2-D method, the 3-D method provides for the non-iterative solution of the incompressible Navier-Stokes equations by means of a fully coupled implicit technique. The solution is calculated on a body fitted computational mesh incorporating a staggered grid methodology. In the staggered grid method, the three components of vorticity are defined at the centers of the computational cell sides, while the velocity components are defined as normal vectors at the centers of the computational cell faces. The staggered grid orientation provides for the accurate definition of the vorticity components at the vorticity locations, the divergence of vorticity at the mesh cell nodes and the conservation of mass at the mesh cell centers. The solution is obtained by utilizing a fractional step solution technique in the three coordinate directions. The boundary conditions for the vorticity and velocity are calculated implicitly as part of the solution. The method provides for the non-iterative solution of the flow field and satisfies the conservation of mass and divergence of vorticity to machine zero at each time step. To test the method, the calculation of simple driven cavity flows have been computed. The driven cavity flow is defined as the flow in an enclosure driven by a moving upper plate at the top of the enclosure. To demonstrate the ability of the method to predict the flow in arbitrary cavities, results will he shown for both cubic and curved cavities.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA-TM-110352 , A-950063 , NAS 1.15:110352
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  • 194
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    Spectral methods on arbitrary grids (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Stable and spectrally accurate numerical methods are constructed on arbitrary grids for partial differential equations. These new methods are equivalent to conventional spectral methods but do not rely on specific grid distributions. Specifically, we show how to implement Legendre Galerkin, Legendre collocation, and Laguerre Galerkin methodology on arbitrary grids.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198158 , NAS 1.26:198158 , ICASE-95-37
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  • 195
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    Acoustic field in unsteady moving media (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: In the interaction of an acoustic field with a moving airframe the authors encounter a canonical initial value problem for an acoustic field induced by an unsteady source distribution, q(t,x) with q equivalent to 0 for t less than or equal to 0, in a medium moving with a uniform unsteady velocity U(t)i in the coordinate system x fixed on the airframe. Signals issued from a source point S in the domain of dependence D of an observation point P at time t will arrive at point P more than once corresponding to different retarded times, Tau in the interval (0, t). The number of arrivals is called the multiplicity of the point S. The multiplicity equals 1 if the velocity U remains subsonic and can be greater when U becomes supersonic. For an unsteady uniform flow U(t)i, rules are formulated for defining the smallest number of I subdomains V(sub i) of D with the union of V(sub i) equal to D. Each subdomain has multiplicity 1 and a formula for the corresponding retarded time. The number of subdomains V(sub i) with nonempty intersection is the multiplicity m of the intersection. The multiplicity is at most I. Examples demonstrating these rules are presented for media at accelerating and/or decelerating supersonic speed.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-198162 , NAS 1.26:198162 , ICASE-95-39
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  • 196
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    Unstructured mesh generation and adaptivity (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: An overview of current unstructured mesh generation and adaptivity techniques is given. Basic building blocks taken from the field of computational geometry are first described. Various practical mesh generation techniques based on these algorithms are then constructed and illustrated with examples. Issues of adaptive meshing and stretched mesh generation for anisotropic problems are treated in subsequent sections. The presentation is organized in an education manner, for readers familiar with computational fluid dynamics, wishing to learn more about current unstructured mesh techniques.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-195069 , NAS 1.26:195069 , ICASE-95-26
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  • 197
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    Algorithms for parallel flow solvers on message passing architectures (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The purpose of this project has been to identify and test suitable technologies for implementation of fluid flow solvers -- possibly coupled with structures and heat equation solvers -- on MIMD parallel computers. In the course of this investigation much attention has been paid to efficient domain decomposition strategies for ADI-type algorithms. Multi-partitioning derives its efficiency from the assignment of several blocks of grid points to each processor in the parallel computer. A coarse-grain parallelism is obtained, and a near-perfect load balance results. In uni-partitioning every processor receives responsibility for exactly one block of grid points instead of several. This necessitates fine-grain pipelined program execution in order to obtain a reasonable load balance. Although fine-grain parallelism is less desirable on many systems, especially high-latency networks of workstations, uni-partition methods are still in wide use in production codes for flow problems. Consequently, it remains important to achieve good efficiency with this technique that has essentially been superseded by multi-partitioning for parallel ADI-type algorithms. Another reason for the concentration on improving the performance of pipeline methods is their applicability in other types of flow solver kernels with stronger implied data dependence. Analytical expressions can be derived for the size of the dynamic load imbalance incurred in traditional pipelines. From these it can be determined what is the optimal first-processor retardation that leads to the shortest total completion time for the pipeline process. Theoretical predictions of pipeline performance with and without optimization match experimental observations on the iPSC/860 very well. Analysis of pipeline performance also highlights the effect of uncareful grid partitioning in flow solvers that employ pipeline algorithms. If grid blocks at boundaries are not at least as large in the wall-normal direction as those immediately adjacent to them, then the first processor in the pipeline will receive a computational load that is less than that of subsequent processors, magnifying the pipeline slowdown effect. Extra compensation is needed for grid boundary effects, even if all grid blocks are equally sized.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-197758 , NAS 1.26:197758 , MCAT-95-15
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  • 198
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    Spectrum and energy transfer in steady Burgers turbulence (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The spectrum, energy transfer, and spectral interactions in steady Burgers turbulence are studied using numerically generated data. The velocity field is initially random and the turbulence is maintained steady by forcing the amplitude of a band of low wavenumbers to be invariant in time, while permitting the phase to change as dictated by the equation. The spectrum, as expected, is very different from that of Navier-Stokes turbulence. It is demonstrated that the far range of the spectrum scales as predicted by Burgers. Despite the difference in their spectra, in matters of the spectral energy transfer and triadic interactions Burgers turbulence is similar to Navier-Stokes turbulence.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-195047 , NAS 1.26:195047 , ICASE-95-13
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  • 199
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    A review of Reynolds stress models for turbulent shear flows (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A detailed review of recent developments in Reynolds stress modeling for incompressible turbulent shear flows is provided. The mathematical foundations of both two-equation models and full second-order closures are explored in depth. It is shown how these models can be systematically derived for two-dimensional mean turbulent flows that are close to equilibrium. A variety of examples are provided to demonstrate how well properly calibrated versions of these models perform for such flows. However, substantial problems remain for the description of more complex turbulent flows where there are large departures from equilibrium. Recent efforts to extend Reynolds stress models to nonequilibrium turbulent flows are discussed briefly along with the major modeling issues relevant to practical naval hydrodynamics applications.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-CR-195054 , NAS 1.26:195054 , ICASE-95-15
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    Baseline experimental investigation of an electrohydrodynamically assisted heat pipe (1995)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The increases in power demand and associated thermal management requirements of future space programs such as potential Lunar/Mars missions will require enhancing the operating efficiencies of thermal management devices. Currently, the use of electrohydrodynamically (EHD) assisted thermal control devices is under consideration as a potential method of increasing thermal management system capacity. The objectives of the currently described investigation included completing build-up of the EHD-Assisted Heat Pipe Test bed, developing test procedures for an experimental evaluation of the unassisted heat pipe, developing an analytical model capable of predicting the performance limits of the unassisted heat pipe, and obtaining experimental data which would define the performance characteristics of the unassisted heat pipe. The information obtained in the currently proposed study will be used in order to provide extensive comparisons with the EHD-assisted performance observations to be obtained during the continuing investigation of EHD-Assisted heat transfer devices. Through comparisons of the baseline test bed data and the EHD assisted test bed data, accurate insight into the performance enhancing characteristics of EHD augmentation may be obtained. This may lead to optimization, development, and implementation of EHD technology for future space programs.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA. Johnson Space Center, National Aeronautics and Space Administration (NASA)(American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1994, Volume 1 15 p (SEE N95-32418; NASA. Johnson Space
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