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  • INSTRUMENTATION AND PHOTOGRAPHY  (2,384)
  • FLUID MECHANICS AND HEAT TRANSFER  (2,146)
  • 1990-1994  (937)
  • 1985-1989  (847)
  • 1980-1984  (1,661)
  • 1970-1974  (1,053)
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  • 1990  (937)
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  • 1990-1994  (937)
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  • 1980-1984  (1,661)
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  • 1
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    Instantaneous velocity field measurement of objects in coaxial rotation using digital image velocimetry (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The instantaneous velocity fields of time-dependent flows, or of a collection of objects moving with spatially varying velocities, can be measured by means of digital image velocimetry (DIV). DIV overcomes several shortcomings of such existing techniques as laser-speckle or particle-image velocimetry. Attention is presently given to numerically generated images representing objects in uniform motion which are then used for the experimental validation of DIV.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : Mechanical behavio
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  • 2
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    Design criteria for small coded aperture masks in gamma-ray astronomy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Most theoretical work on coded aperture masks in X-ray and low-energy gamma-ray astronomy has concentrated on masks with large numbers of elements. For gamma-ray spectrometers in the MeV range, the detector plane usually has only a few discrete elements, so that masks with small numbers of elements are called for. For this case it is feasible to analyze by computer all the possible mask patterns of given dimension to find the ones that best satisfy the desired performance criteria. A particular set of performance criteria for comparing the flux sensitivities, source positioning accuracies and transparencies of different mask patterns is developed. The results of such a computer analysis for masks up to dimension 5 x 5 unit cell are presented and it is concluded that there is a great deal of flexibility in the choice of mask pattern for each dimension.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); A295; 477-488
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  • 3
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    An error analysis of least-squares finite element method of velocity-pressure-vorticity formulation for Stokes problem (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A theoretical proof of the optimal rate of convergence for the least-squares method is developed for the Stokes problem based on the velocity-pressure-vorticity formula. The 2D Stokes problem is analyzed to define the product space and its inner product, and the a priori estimates are derived to give the finite-element approximation. The least-squares method is found to converge at the optimal rate for equal-order interpolation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 84; 3, De
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  • 4
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    Isotopically enriched germanium detectors for astrophysical gamma-ray spectroscopy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A study is presented of the instrumental background in astrophysical gamma-ray spectrometers using isotopically enriched germanium detectors. Calculations show that the beta-decay background, which is the largest component between approximately 0.1 and 1.0 MeV in balloonborne and satellite spectrometers, is dominated by the activation of Ge-74. This component can be reduced by an order of magnitude using detectors enriched to more than 80 percent in (Ge-70). The predicted reduction in the total background for current balloonborne instruments is more than a factor of 1.7 between 0.2 and 1.0 MeV. For future satellite instruments, the reduction in this energy range is by more than a factor of 5.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); 292; 505-516
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  • 5
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    Experimental and computational surface and flow-field results for an all-body hypersonic aircraft (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Personnel from NASA Ames Research Center presented a paper on establishing a benchmark experimental data base for generic hypersonic vehicle shape for validation and/or calibration of advanced computational fluid dynamics computer codes. The need for this capability is based on a requirement for extensive hypersonic data to fully validate CFD codes to be used for NASP and other hypersonic vehicles. The use of wind tunnel models in the Ames 3.5-ft Hypersonic Wind Tunnel to obtain pertinent surface and flow-field data over a broad range of test conditions is described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 126-161
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  • 6
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    NASA. Lewis Research Center/IFMD inlet duct and nozzle high speed validation experiments (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Personnel from NASA Lewis Research Center spoke on the subject of inlet duct and nozzle high speed validation experiments to include crossing shocks and boundary layer interaction, unsteady shock/boundary layer interactions, and vortex generators. Attention was also paid to the subjects of high speed mixing and transition ducts. Specific application was made to the NASP hypermixing concepts.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 197-231
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  • 7
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    Summary of NASA. Lewis Research Center validation efforts (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: NASA Lewis Research Center personnel presented a summary of LeRC validation experiments. The subjects discussed included: iced wing, linear transonic cascade, transition duct aerodynamics, transition duct heat transfer, low speed centrifugal compressor, turbomachinery blade row interactions, and three dimensional fluid mechanics.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 100-125
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  • 8
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    NASA. Langley Research Center CFD code validation program overview (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: A presentation by Langley Research Center covered subjects of: LaRC approach to CFD code validation, experimental CFD perceptions, CFD code validation program experiment, and highlights of the experiment. The objective of the validation program and the approach taken are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 1-21
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  • 9
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    NASA low speed centrifugal compressor (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: The flow characteristics of a low speed centrifugal compressor were examined at NASA Lewis Research Center to improve understanding of the flow in centrifugal compressors, to provide models of various flow phenomena, and to acquire benchmark data for three dimensional viscous flow code validation. The paper describes the objectives, test facilities' instrumentation, and experiment preliminary comparisons.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: 2nd NASA CFD Validation Workshop; p 232-256
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  • 10
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    Flow over a rearward facing step (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: The characteristics of flow over a rearward facing step is discussed in a paper presented by NASA Lewis Research Center personnel. The objective is to obtain data which will be used for validation of Direct Numerical Simulations being developed at NASA Langley and Ames. Two phases of the work are identified as a study of large scale structures in the flow using hot-wire/cold wire techniques and the development of a statistical data base for using three-component laser velocimetry.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 182-196
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  • 11
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    Overview of CFD flow modeling and validation: NASA. Ames Research Center (1990)
    In:  CASI
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    Publication Date: 2004-12-04
    Description: NASA Ames Center personnel presented data on stages of code development and corresponding experiments in the application of computational fluid dynamics for aeronautical investigations. Specific subjects included algorithms, grid generation, facilities, instrumentation, and data acquisition. Numerical simulation and flow modelling were described to show the procedure for calibration and validation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 45-69
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  • 12
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    Status of NASA. Marshall Space Flight Center CFD application and validation activities (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: NASA Marshall Space Flight Center personnel presented a paper on the status of MSFC computational fluid dynamics application and validation activities. Subjects discussed included the Space Shuttle Main Engine studies, unsteady multistage turbine loads, fuel pump discharge volutes, and injector LOX inlet results based on fundamental flows, subcomponents, and interactive components/systems.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, 2nd NASA CFD Validation Workshop; p 70-99
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  • 13
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    Fluid management in the optimization of space construction (1990)
    In:  CASI
    Details
    Publication Date: 2004-10-02
    Description: Fluid management impacts strongly on the optimization of space construction. Large quantities of liquids are needed for propellants and life support. The mass of propellant liquids is comparable to that required for the structures. There may be a strong dynamic interaction between the stored liquids and the space structure unless the design minimizes the interaction. The constraints of cost and time required optimization of the supply/resupply strategy. The proper selection and design of the fluid management methods for: slosh control; stratification control; acquisition; transfer; gauging; venting; dumping; contamination control; selection of tank configuration and size; the storage state and the control system can improve the entire system performance substantially. Our effort consists of building mathematical/computer models of the various fluid management methods and testing them against the available experimental data. The results of the models are used as inputs to the system operations studies. During the past year, the emphasis has been on modeling: the transfer of cryogens; sloshing and the storage configuration. The work has been intermeshed with ongoing NASA design and development studies to leverage the funds provided by the Center.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Second Annual Symposium; p 412-433
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  • 14
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    Unstructured finite element mesh generation and adaptive procedures for CFD (1990)
    In:  CASI
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    Publication Date: 2011-10-14
    Description: A method is described for generating unstructured meshes of triangles or tetrahedra for computational domains of complex geometrical shape. To illustrate the power of the approach, it is applied to the solution of flows past several complete aircraft configurations. The advocated approach allows for the natural incorporation of mesh adaptivity and this is demonstrated for both inviscid and viscous computations in two and three dimensions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Applications of Mesh Generation to Complex 3-D Configurations; 12 p
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  • 15
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    Applications of algebraic grid generation (1990)
    In:  CASI
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    Publication Date: 2011-10-14
    Description: Techniques and applications of algebraic grid generation are described. The techniques are univariate interpolations and transfinite assemblies of univariate interpolations. Because algebraic grid generation is computationally efficient, the use of interactive graphics in conjunction with the techniques is advocated. A flexible approach, which works extremely well in an interactive environment, called the control point form of algebraic grid generation is described. The applications discussed are three-dimensional grids constructed about airplane and submarine configurations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Applications of Mesh Generation to Complex 3-D Configurations; 12 p
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  • 16
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    A defect stream function formulation for compressible turbulent boundary layers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Progress to date on the development of a method for turbulent, wall-bounded flow which uses the defect stream function formulation in the outer layer and an analytic law of the wall and wake formulation in the inner region is reviewed. This two-formulation approach avoids the need to computationally resolve the high-gradient inner layer. One of the most appealing recent developments is the transformation of the compressible governing equation for the defect stream function into a linear, second-order differential equation which has analytic solutions for many problems of practical interest. Numerical and analytic results for incompressible and compressible flows are shown to be in excellent agreement with experimental results. In this paper the two-formulation approach is applied to primitive-variable computations. Excellent comparisons with experiment are presented for two compressible flat plate flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 17
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    Quasi-coherent structures in the turbulent boundary layer. II - Verification and new information from a numerically simulated flat-plate layer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 18
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    Velocity and pressure fields associated with near-wall turbulence structures (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Computer generated databases containing velocity and pressure fields in three-dimensional space at a sequence of time-steps, were used for the investigation of near-wall turbulence structures, their space-time evolution, and their associated pressure fields. The main body of the results were obtained from simulation data for turbulent channel flow at a Reynolds number of 180 (based on half-channel height and friction velocity) with a grid of 128 x 129 x and 128 points. The flow was followed over a total time of 141 viscous time units. Spanwise centering of the detected structures was found to be essential in order to obtain a correct magnitude of the associated Reynolds stress contribution. A positive wall-pressure peak is found immediately beneath the center of the structure. The maximum amplitude of the pressure pattern was, however, found in the buffer region at the center of the shear-layer. It was also found that these flow structures often reach a maximum strength in connection with an asymmetric spanwise motion, which motivated the construction of a conditional sampling scheme that preserved this asymmetry.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 19
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    Quasi-coherent structures in the turbulent boundary layer. I - Status report on a community-wide summary of the data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A review is presented of the approach, motivation and early results of a reevaluation of the knowledge collected by the research community during thirty years of research on the structure of turbulent boundary layers. Four distinctions or criteria concerning the need to improve the practices in this field are discussed: data versus inferences, possible versus actual versus significant events, one structure versus many, and one or two flows versus the totality of data. Attention given to the known quasi-coherent structures show that three factors significantly reduce the information available from laboratory data as a basis for forming a complete model of the quasi-coherent structure in the turbulent boundary layer: (1) the necessity to ensemble average probe output with resulting loss of phase information, (2) the inability to see more than one or two of the various types of structures simultaneously, and (3) the inability to see the spatial relations between the various quasi-coherent structures resulting from (1) and (2).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 20
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    Statistical analysis of near-wall structures in turbulent channel flow (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The two-point correlation tensor is used to analyze near-wall structures in turbulent channel flow. Simulation results have been utilized to obtain the correlation tensor with sufficient spatial resolution to permit accurate differentiation for computing the vorticity correlation, and the resolution of sharp features such as the shear layer and its corresponding region of spanwise vorticity. Proper orthogonal decomposition and stochastic estimation were observed to yield similar results when appropriate conditions were employed for the estimation. Resulting structures were such that they would be detected by standard conditional sampling methods. The results of decomposing the vorticity field and the velocity field were significantly different, indicating that if a coherent structure is found that dominates the velocity fields, the curl of that velocity structure will not dominate the vorticity field.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 21
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    Similarity of organized structures in turbulent shear flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent analysis of databases generated by direct numerical simulations of homogeneous turbulent shear flows have revealed the presence of coherent structures similar to those in turbulent boundary layers. In this paper these findings and tentative conclusions on their significance are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 22
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    Unsteady viscous flow around a circular cylinder found by the hopscotch scheme on a vector processing machine (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The hopscotch scheme is examined to see whether it can compete effectively with implicit schemes for the integration of the Navier-Stokes equations on a vector processing machine. This scheme is stable as long as the Courant number is less than or equal to one and it does not underestimate viscous effects. The accuracy of the scheme is tested on one- and two-dimensional problems whose exact solutions are known. The scheme is then used to simulate flows around a circular cylinder with Reynolds numbers 200, 500 and 1000.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Applied Numerical Mathematics (ISSN 0168-9274); 6; 195-208
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  • 23
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    Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be less than 2 percent, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 4873-488
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  • 24
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    Interfacial dynamics of two liquids under an oscillating gravitational field (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The evolution of two miscible liquids meeting at an initially sharp interface inside a cavity under microgravity g-jitter conditions is studied numerically. The response of the interface and kinematics of the flowfield to various g-jitter accelerations and aspect ratio variations is shown. The interface region acts like a vortex source sheet, and it can be unstable to Kelvin-Helmholtz and Rayleigh-Taylor instabilities. The vortices produced along the interface can serve as a stirring mechanism to promote local mixing. Below the critical Stokes-Reynolds number, the destabilization of the interface results in deformation into wavy structures. In some parameter regions, these structures oscillate in time; in others, they are quasi-steady. Above the critical Stokes-Reynolds number, 'chaotic' instability results, and the interface breaks into concentration pockets. The morphology of the initial breakup is similar to observed Rayleigh-Taylor instability. Subsequent mixing of the two fluids after the breakup of the interface is then very rapid.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 1933-194
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  • 25
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    Stability of an oscillated fluid with a uniform density gradient (1990)
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    Publication Date: 2011-08-19
    Description: Instabilities in a fluid with a constant density gradient that is subject to arbitrarily oriented oscillatory accelerations are considered. With the Boussinesq approximation and for the case of an unbounded fluid, transformation to Lagrangian coordinates allows the reduction of the problem to an ordinary differential equation for each three-dimensional wavenumber. The problem has three parameters: the nondimensional amplitude R of the base-state oscillation, the nondimensional level of background steady acceleration, which for some cases can be represented in terms of a local (in time) Richardson number Ri, and the Prandtl number Pr. Some general bounds on stability are derived. For Pr = 1 closed-form solutions are found for impulse (delta function) accelerations and a general asymptotic solution is constructed for large R and general imposed accelerations. The asymptotic solution takes advantage of the fact that at large R wave growth is concentrated at 'zero points'. These are times when the effective vertical wavenumber passes through zero. Kelvin-Helmholtz instabilities are found to dominate at low R, while Rayleigh-Taylor instabilities dominate at high R. At high R, the uniform shear of the Kelvin-Helmholtz case tends to distort and weaken instability waves. With unsteady flows, Ri = 1/4 is no longer an instability limit. Significant instabilities have been found for sinusoidal forcing for Ri up to 0.6.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 219; 449-468
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  • 26
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    Advanced CCD imager technology for use from 1 to 10,000 A (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A low-noise, high-sensitivity charge-coupled-device (CCD) technology for imaging applications extending from the soft X-ray (1 A) to the near-infrared (10,000 A) regimes was developed together with a fabrication technology for making back-illuminated versions of these devices with quantum efficiencies as high as 90 percent from 5000 to 7000 A. The efforts have focused on two devices, a 64 x 64 pixel back-illuminated imager with two output ports that operates at 2000 frames per second with 23 electrons read noise, and a larger device, with 420 x 420 pixel format, designed for lower frame rates with noise as low as 1.5 electrons and used at visible, UV, and X-ray wavelengths. Applications to plasma diagnostics include Thomson scattering and high-frame-rate imaging in the visible, as well as X-ray imaging and bolometry.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 2744-274
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  • 27
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    Riblets (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In addition to characterizing the various concepts reported in the literature on longitudinally-ribbed surface for aerodynamic surface drag reduction, the present development status evaluation of this technology correlates all available experimental data. An analysis of these data is then conducted to ascertain the parameters most directly involved in drag reduction, and to evaluate the effects which have thus far been exerted on turbulent boundary layer structures. Such advanced riblet techniques as compound and three-dimensional riblets, riblets in combination with large-eddy breakup devices, and riblets with suction/blowing, are also discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 28
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    Active wave control of boundary-layer transition (1990)
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    Publication Date: 2011-08-19
    Description: The physical processes involved in the boundary layer instability-generation and transition process seem to pose basic restrictions on the implementation of active, wave-based transition-control methods. While suppression short of elimination is possible by these means for primary disturbances, wave-interaction instabilities demand that the control be implemented almost immediately after the appearance of primary disturbances; even slight delays can negate the intended beneficial effects, and this basic problem is exacerbated at the higher Reynolds numbers typical of aircraft in cruising flight. Three-dimensional disturbances are noted to be important in this context, together with the continuous regeneration of TS waves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 29
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    Recent advances, trends and new perspectives via enthalpy-based finite element formulations for applications to solidification problems (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present paper describes recent advances and trends in finite element developments and applications for solidification problems. In particular, in comparison to traditional methods of approach, new enthalpy-based architectures based on a generalized trapezoidal family of representations are presented which provide different perspectives, physical interpretation and solution architectures for effective numerical simulation of phase change processes encountered in solidification problems. Various numerical test models are presented and the results support the proposition for employing such formulations for general phase change applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 30; 803-820
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  • 30
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    Inviscid flux-splitting algorithms for real gases with non-equilibrium chemistry (1990)
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    Publication Date: 2011-08-19
    Description: Formulations of inviscid flux splitting algorithms for chemical nonequilibrium gases are presented. A chemical system for air dissociation and recombination is described. Numerical results for one-dimensional shock tube and nozzle flows of air in chemical nonequilibrium are examined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 371-395
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  • 31
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    Ternary baroeffect with a nondiffusing component (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A systematic analysis is developed which describes the isothermal counterdiffusion of two gases in the presence of a third nondiffusing gas. Four distinct regimes are identified for diffusive slip. The nondiffusing gas reduces the pressure drop in all cases, whether it raises or lowers the mean density. The gas leads to nonzero diffusive slip even in the limit of very disparate masses for the diffusing gases. The implications of these findings for controlling concentration creep in crystal growth are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 65; 1587-159
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    Diagonally inverted lower-upper factored implicit multigrid scheme for the three-dimensional Navier-Stokes equations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 1642-164
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    Solitons induced by boundary conditions from the Boussinesq equation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The behavior of solitons induced by boundary excitation is investigated at various time-dependent conditions and different unperturbed water depths, using the Korteweg-de Vries (KdV) equation. Then, solitons induced from Boussinesq equations under similar conditions were studied, making it possible to remove the restriction in the KdV equation and to treat soliton head-on collisions (as well as overtaking collisions) and reflections. It is found that the results obtained from the KdV and the Boussinesq equations are in good agreement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1574-158
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    Hopf bifurcation in the driven cavity (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The algorithm employed in the present incompressible two-dimensional calculations of an impulsively-started lid-driven cavity has its basis in the time-dependent stream-function equation. While a Crank-Nicholson differencing scheme is used for the diffusion terms, the Adams-Bashforth scheme is used for the convection terms. The periodic asymptotic solutions obtained for Reynolds numbers of 5000 and 10,000 are found to be precisely periodic; it is demonstrated that they have reached asymptotic states. The indicators of that achievement are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 219-261
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    A novel sample-positioning system for microgravity application (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper proposes a novel method for sample positioning in containerless processing at microgravity, using a system based on pulsed lasers. The method has two attributes. First, by generating beams that cancel out vectorially, the suspended material can be heated without being accelerated, a feature that can be used in melting and heat-treatment applications. Second, the specimen can be positioned within a fairly large work space. It is emphasized that this method can service a regime unfulfilled by the other levitation methods, such as electromagnetic levitation, active magnetic suspension, acoustic levitation, of electrostatic suspension.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 2251-225
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    Containments for liquids at zero gravity (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theory proposed by Concus and Finn (1974) and recently developed by Finn (1983 and 1984) yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. These criteria were applied by Concus and Finn to three container geometries: the bathtub, the trapezoid, and the keyhole. It is possible to find geometrical criteria that promise a liquid interface of finite height, with the base still covered with liquid, or a liquid interface of infinite height, with the liquid wetting a well defined portion of the wall. In the present work, calculations are presented for a fourth geometry, the non-concentric cylinders. In addition, the earlier calculations of Concus and Finn are extended, and a unified graphical presentation of all four geometries is given that can be used directly for the design of containments for liquids at zero gravity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Microgravity Science and Technology (ISSN 0938-0108); 3; 13-23
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    A spectrum model for weakly anisotropic turbulence (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple model, parameterized by the Reynolds stress anisotropy, is proposed for the spectrum of weakly anisotropic turbulence. It contains a model constant that affects its region of realizability. This spectrum model is used to derive a one-point closure to the rapid pressure-strain term. The derived pressure-strain model is linear in the Reynolds stress anisotropy and is of the same form as the closure model of Launder et al. (1975). The spectrum model becomes unrealizable in some regions of wave space for sufficiently large anisotropy of the Reynolds stress, and this is used to infer the region of validity of the linear closure model. It is found that the extent of the valid region is very small when the model constant is set to match rapid distortion theory, and largest for a model-constant set close to the value suggested by LRR. However, even the largest valid domain does not extend very far from isotropy, suggesting inherent weakness in the linear pressure-strain models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1500-150
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    Simultaneous multivelocity component laser Doppler velocimetry using one digital frequency processor (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Digital frequency processing used in conjunction with optical frequency shifting is an ideal way to achieve simultaneous multivelocity component measurements in laser Doppler velocimetry. This becomes obvious once realized that multivelocity component information at different frequency offsets can be obtained directly from the composite frequency spectrum of a single-channel digital frequency processor. The approach has numerous advantages over the very popular approach of using a different laser wavelength, photodetector, and signal processor for each velocity component.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 1989
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    A technique for measurement of instantaneous heat transfer in steady-flow ambient-temperature facilities (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An experimental technique is described for obtaining time-resolved heat flux measurements with high-frequency response (up to 100 kHz) in a steady-flow ambient-temperature facility. The heat transfer test object is preheated and suddenly injected into an established steady flow. Thin-film gages deposited on the test surface detect the unsteady substrate surface temperature. Analog circuitry designed for use in short-duration facilities and based on one-dimensional semiinfinite heat conduction is used to perform the temperature/heat flux transformation. A detailed description of substrate properties, instrumentation, experimental procedure, and data reduction is given, along with representative results obtained in the stagnation region of a circular cylinder subjected to a wake-dominated unsteady flow. An in-depth discussion of related work is also provided.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Experimental Thermal and Fluid Science (ISSN 0894-1777); 3; 416-430
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  • 40
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    Near-wall turbulence model and its application to fully developed turbulent channel and pipe flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A near-wall turbulence model and its incorporation into a multiple-timescale turbulence model are presented. The near-wall turbulence model is obtained from a k-equation turbulence model and a near-wall analysis. In the method, the equations for the conservation of mass, momentum, and turbulent kinetic energy are integrated up to the wall, and the energy transfer and the dissipation rates inside the near-wall layer are obtained from algebraic equations. Fully developed turbulent channel and pipe flows are solved using a finite element method. The computational results compare favorably with experimental data. It is also shown that the turbulence model can resolve the overshoot phenomena of the turbulent kinetic energy and the dissipation rate in the region very close to the wall.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Numerical Heat Transfer, Part B: Fundamentals (ISSN 1040-7790); 17; 101-122
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    Measurement of Allan variance and phase noise at fractions of a millihertz (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Although the measurement of Allan variance of oscillators is well documented, there is a need for a simplified system for finding the degradation of phase noise and Allan variance step-by-step through a system. This article describes an instrumentation system for simultaneous measurement of additive phase noise and degradation in Allan variance through a transmitter system. Also included are measurements of a 20-kW X-band transmitter showing the effect of adding a pass tube regulator.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 1720-172
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  • 42
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    Implicit flux-split schemes for the Euler equations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 973
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    Electrooptic modulation methods for high sensitivity tunable diode laser spectroscopy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A CdTe phase modulator and low power RF sources have been used with Pb-salt tunable diode lasers operating near 8 microns to generate optical sidebands for high sensitivity absorption spectroscopy. Sweep averaged, first-derivative sample spectra of CH4 were acquired by wideband phase sensitive detection of the electrooptically (EO) generated carrier-sideband beat signal. EO generated beat signals were also used to frequency lock the TDL to spectral lines. This eliminates low frequency diode jitter, and avoids the excess laser linewidth broadening that accompanies TDL current modulation frequency locking methods.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 2282-228
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    Numerical simulations of soft and hard turbulence - Preliminary results for two-dimensional convection (1990)
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    Publication Date: 2011-08-19
    Description: Results on the transition from soft to hard turbulence in simulations of two-dimensional Boussinesq convection are reported. The computed probability densities for temperature fluctuations are exponential in form in both soft and hard turbulence, unlike what is observed in experiments. In contrast, a change is obtained in the Nusselt number scaling on Rayleigh number in good agreement with the three-dimensional experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 64; 2370-237
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  • 45
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    Modeling of confined turbulent fluid-particle flows using Eulerian and Lagrangian schemes (1990)
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    Publication Date: 2011-08-19
    Description: Two important aspects of fluid-particulate interaction in dilute gas-particle turbulent flows (the turbulent particle dispersion and the turbulence modulation effects) are addressed, using the Eulerian and Lagrangian modeling approaches to describe the particulate phase. Gradient-diffusion approximations are employed in the Eulerian formulation, while a stochastic procedure is utilized to simulate turbulent dispersion in the Lagrangina formulation. The k-epsilon turbulence model is used to characterize the time and length scales of the continuous phase turbulence. Models proposed for both schemes are used to predict turbulent fully-developed gas-solid vertical pipe flow with reasonable accuracy.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 33; 691-701
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    Image recovery from edge primitives (1990)
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    Publication Date: 2011-08-19
    Description: A method for extracting edge primitives from Mach-band patterns is presented together with a method for recovering image representations of features outlined by the edge boundaries. The accuracy, stability, and resolution of these representations are assessed. Since these representations are most commonly used in characterizing targets, this method of low-level processing offers new opportunities for computer vision and high data-compressing coding. Two bandpass filters are considered, the spatially invariant Laplacian of Gaussian filter and spatially variant intensity-dependent spatial (IDS) summation. It is shown that the recovery from the IDS bandpass data is particularly advantageous in applications for which robustness to local and temporal variations in illumination is important. It is concluded that the edge primitives extracted from bandpassed images can be an efficient way to store, transmit, and represent images.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Society of America, Journal, A: Optics and Image Science (ISSN 0740-3232); 7; 898-911
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    The vibrating ribbon problem revisited (1990)
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    Publication Date: 2011-08-19
    Description: A revised formal solution of the vibrating ribbon problem of hydrodynamic stability is presented. The initial formulation of Gaster (1965) is modified by application of the Briggs method and a careful treatment of the complex double Fourier transform inversions. Expressions are obtained in a natural way for the discrete spectrum as well as for the four branches of the continuous spectra. These correspond to discrete and branch-cut singularities in the complex wavenumber plane. The solutions from the continuous spectra decay both upsteam and downstream of the ribbon, with the decay in the upstream direction being much more rapid than that in the downstream direction. Comments and clarification of related prior work are made.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 213; 531-547
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    Numerical analysis of three-dimensional viscous internal flows (1990)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 798-806
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    Variable specific heat and thermal relaxation parameter in hyperbolic heat conduction (1990)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 252-255
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    Survey of simulation and diagnostic techniques for hypersonic nonequilibrium flows (1990)
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    Publication Date: 2011-08-19
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 129-140
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    Implicit methods for the Navier-Stokes equations (1990)
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    Publication Date: 2011-08-19
    Description: Numerical solutions of the Navier-Stokes equations using explicit schemes can be obtained at the expense of efficiency. Conventional implicit methods which often achieve fast convergence rates suffer high cost per iteration. A new implicit scheme based on lower-upper factorization and symmetric Gauss-Seidel relaxation offers very low cost per iteration as well as fast convergence. High efficiency is achieved by accomplishing the complete vectorizability of the algorithm on oblique planes of sweep in three dimensions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computing Systems in Engineering (ISSN 0956-0521); 1; 2-4,
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    Visualization of fluid dynamics at NASA Ames (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Some of the hardware and software tools and techniques in use at NASA's numerical aerodynamic simulation facility for the analysis of computational fluid dynamics are described. The visualization process can be illustrated by video tapes and stereo pictures. Although these visualization tools have dramatically improved the ability to conduct research in fluid dynamics, a comparison of the current environment for analysis with an 'ideal' environment illustrates that there are still major improvements that should be made. The most time-consuming task in future analyses of the increasingly complex computer simulations will be the extraction and clear display of the key features. In addition, the interface between the workstation and the scientist should be improved significantly. Current research on techniques for creating these improvements is described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computing Systems in Engineering (ISSN 0956-0521); 1; 2-4,
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    A resistance strain gage with repeatable and cancellable apparent strain for use to 1500 F (1990)
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    Publication Date: 2011-08-19
    Description: A temperature compensated static strain gauge, which is fabricated from Pd13Cr alloy and a Pt compensator, is being developed and has been tested over a temperature range to 1500 F at NASA-Lewis. The PdCr compensated strain gage has significantly lower apparent strain to 500 F than other high temperature strain gages. The PdCr compensated gage is protected from oxidation by a flame-sprayed alumina-4 wt pct zirconia overcoating. Test Results to 1500 F indicate apparent strain variations of less than 250 micro-epsilon and reproducibility between thermal cycles within 50 micro-epsilon. The apparent strain of the coated PdCr compensated gage can be predicted and cancelled due to its reproducibility and low value.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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    Spacelab qualified infrared imager for microgravity science applications (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Lewis Research Center is developing, under contract, a Spacelab (manned module in the Space Shuttle payload bay) qualified infrared imager for noncontact surface temperature measurement in the Surface Tension Driven Convection Experiment, a microgravity fluid physics experiment. A versatile design philosophy was used in order to provide other experiments with essentially an off the shelf Shuttle qualified instrument, eliminating the duplication of the rigorous development and flight qualification processes. An Inframetrics Model 600 Scanning Infrared Radiometer is being modified to satisfy both experimental and flight requirements, while maintaining the basic performance parameters of the commercial instrument. The modifications include an efficient, low power closed cycle cryogenic cooler to cool the detector, a ruggedized scanner mechanism, 8 bit A/D conversion, Mil-STD components (where possible), size and weight optimization, and the addition of a microprocessor to perform automatic gain control. Features such as detector spectral response, the addition of spectral filters, and target temperature ranges could easily be changed to make this instrument useful as both a qualitative and quantitative diagnostic tool for Spacelab microgravity experiments, in combustion and fluid physics.
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    Electronically scanned multichannel pressure transducer system for cryogenic environments (1990)
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    Publication Date: 2011-08-19
    Description: Research into the application of custom doped piezoresistive silicon pressure sensors has led to a multichannel pressure sensor design that will operate accurately and reliably at cryogenic temperatures. The thermal effects upon multichannel pressure sensors are mapped by thermal calibrations and are represented by sets of nth order coefficients specific to each sensor. The thermal offset and sensitivity variations are corrected by computer algorithms which scan the sensors, recall correction coefficients from thermally induced sensor variations, and apply these to correct the sensor's output measurement uncertainty to within 0.5 percent of full scale output for combined offset and sensitivity. A prototype sensor system has been fabricated, and performance test data are presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Cryogenics (ISSN 0011-2275); 30; 1104-110
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    A synchronous strobed laser light sheet for helicopter model rotor flow visualization (1990)
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    Publication Date: 2011-08-19
    Description: A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ISA Proceedings (ISSN 0227-7576); 9-22
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    Particle image fields and partial coherence (1990)
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    Publication Date: 2011-08-19
    Description: The accuracy of Young's fringe method for reducing velocity field data is compromized by a spatially incoherent background field which originates in the random locations of the seeding particles. The probability density function for the spatial frequency cutoff of this background is derived as a function of the particle count, the distribution governing the power in each frequency interval is derived, and conditions are found under which the Van Cittert-Zernike theorem applies. The background field resembles the far field of a partially coherent source in the high particle count limit, but departs significantly at low and moderate counts.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 5282-529
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    Nonlinear phase-space diffusion approach to turbulent organized structures (1990)
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    Publication Date: 2011-08-19
    Description: The study deals with the approximation of the effect of all velocity-increment moments on the spatial evolution of the pdf for maximally correlated structures by the effect of the second moment alone by assuming independence of separated length scales. The dependence of the two-point velocity statistics on length-scale or separation is found to be governed by the gradients of the stress, rather than of the velocity. This may provide a new approach for predicting the domain patterns observed in turbulent flows and a new means of characterizing or classifying different structures, namely, by their nonlinear diffusion coefficient.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Canadian Journal of Physics (ISSN 0008-4204); 68; 723-725
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    Effect of metallic coatings on the thermal contact conductance of turned surfaces (1990)
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    Publication Date: 2011-08-19
    Description: An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 microns for indium, 1.5 to 2.5 microns for lead, and 0.2 to 0.5 microns for tin. The enhancement factors for thermal contact conductance were found to be on the order of 700, 400, and 50 percent, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, additional experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 112; 864-871
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    Measurement intercomparison of the JPL and GSFC stratospheric ozone lidar systems (1990)
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    Publication Date: 2011-08-19
    Description: For approximately one month during October and November 1988 the NASA Goddard Space Flight Center mobile lidar system was brought to the Jet Propulsion Laboratory, Table Mountain Facility, to make side-by-side measurements with the JPL lidar of stratospheric ozone concentration profiles. Measurements were made by both excimer laser DIAL systems on fifteen nights during this period. The results showed good agreement of the ozone profiles measured between 20- and 40-km altitude. This is believed to be the first reported side-by-side measurement intercomparison of two stratospheric ozone lidar systems.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 4671-467
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    A probe for real-time images of particle beams and their analyses in a merged-beams apparatus (1990)
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    Publication Date: 2011-08-19
    Description: A real-time charged particle beam probe was developed, which can be used both as a beam diagnostic (beam tuning) and to quantitatively determine the three-dimensional density distribution of a beam. The probe consists of a microchannel plate, an aluminized phosphor screen deposited on a fiber-optic faceplate, a flexible fiber-optic bundle, and a charge injection device (CID) in tandem. Digital or analog video output of the CID is fed into a computer or oscilloscope, respectively, for analysis or observation. The probe can be moved continuously along the beams' paths to obtain 'pictures' of the beam at any desired interval, thus giving three-dimensional form factors. The beams, singly or simultaneously, may be observed on the monitor facilitating the task of beam adjustment for optimum overlap. The digital output is used for quantitative computation of the beam overlaps. The device is linear with beam intensity, but the performance degrades with time due to beam damage of the microchannel plate.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 3372-337
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    Influence of geometric features on the performance of pressure-swirl atomizers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The spray characteristics of several different simplex pressure-swirl nozzles are examined using water as the working fluid. Measurements of mean drop size, drop-size distribution, effective spray cone angle, and circumferential liquid distribution are carried out over wide ranges of injection pressure. Eight different nozzles are employed in order to achieve a wide variation in the length/diameter ratio of the final discharge orifice. Generally, it is found that an increase in discharge orifice length/diameter ratio, l(o)/d(o), increases the mean drop size in the spray and reduces the spray cone angle. The circumferential liquid distribution is most uniform when l(o)/d(o) = 2. If l(o)/d(o) is raised above or lowered below this optimum value, the circumferential uniformity of the liquid distribution is impaired. The observed effects of l(o)/d(o) on spray characteristics are generally the same regardless of whether the change in l(o)/d(o) is accomplished by varying l(o) or d(o).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Engineering for Gas Turbines and Power (ISSN 0022-0825); 112; 579-584
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    Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Physics Letters (ISSN 0003-6951); 57; 1870-187
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    Direct numerical simulation of a three-dimensional turbulent boundary layer (1990)
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    Publication Date: 2011-08-19
    Description: The effects of transverse strain on an initially two-dimensional turbulent boundary layer are studied in a direct numerical simulation of a planar channel flow with impulsively started transverse pressure gradient. Consistent with experiments in three-dimensional boundary layers, the simulation shows a decrease in the Reynolds shear stress with increasing transverse strain. Also, the directions of the Reynolds shear stress vector and the mean velocity gradient vector were found to differ. In addition, the simulation shows a drop in the turbulent kinetic energy. Terms in the Reynolds stress transport equations were computed. The balances indicate that the decrease in turbulent kinetic energy is a result of a decrease in turbulence production, along with an increase in turbulent dissipation. Intuitive reasoning and current turbulence models would predict an increase in kinetic energy along with increases in production and dissipation rates as a result of increased mean-flow strain rate. Later in the evolution of the flow, both turbulence production and dissipation increase.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 1846-185
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    Time-dependent boundary conditions for hyperbolic systems. II (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A general boundary condition formalism is developed for all types of boundary conditions to which hyperbolic systems are subject; the formalism makes possible a 'cookbook' approach to boundary conditions, by means of which novel boundary 'recipes' may be derived and previously devised ones may be consulted as required. Numerous useful conditions are derived for such CFD problems as subsonic and supersonic inflows and outflows, nonreflecting boundaries, force-free boundaries, constant pressure boundaries, and constant mass flux. Attention is given to the computation and integration of time derivatives.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 89; 439-461
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    Reference NO2 calibration system for ground-based intercomparisons during NASA's GTE/CITE 2 mission (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An NO2 calibration system, based on a permeation device and a two-stage dynamic dilution system, was designed, constructed, and characterized at the National Bureau of Standards. In this system, calibrant flow entering the second stage was controlled without contacting a metal flow controller, and permeation oven temperature and flow were continuously maintained, even during transport. The system performance and the permeation emission rate were characterized by extensive laboratory tests. This system was capable of accurately delivering known NO2 concentrations in the ppbv and sub-ppbv concentration range with a total uncertainty of approximately 10 percent. The calibration system was placed on board NASA research aircraft at both the Wallops Island and Ames research facilities. There it was employed as the reference standard in NASA's Global Tropospheric Experiment/Chemical Instrumental Test and Evaluation 2 mission in August 1986.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 10139-10
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    Long-wave morphological instabilities in the directional solidification of a dilute binary mixture (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Long-wave instabilities in a directionally-solidified binary mixture may occur in several limits. Sivashinsky (1983) identified a small-segregation-coefficient limit and obtained a weakly nonlinear evolution equation governing subcritical two-dimensional bifurcation. Brattkus and Davis (1988) identified a near-absolute-stability limit and obtained a strongly nonlinear evolution equation governing supercritical two-dimensional bifurcation. The present investigation identifies a third strongly nonlinear evolution equation, arising in the small-segregation-coefficient, large-surface-energy limit. This equation links both of the former and describes the change from the sub- to super-critical bifurcations. This study sets the previous long-wave analyses into a logical framework.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: SIAM Journal on Applied Mathematics (ISSN 0036-1399); 50; 420-436
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  • 68
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    On the Lagrangian description of unsteady boundary-layer separation. II - The spinning sphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theory to explain the initial stages of unsteady separation was proposed by Van Dommelen and Cowley (1989). This theory is verified for the separation process that occurs at the equatorial plane of a sphere or a spheroid which is impulsively spun around an axis of symmetry. A Lagrangian numerical scheme is developed which gives results in good agreement with Eulerian computations, but which is significantly more accurate. This increased accuracy, and a simpler structure to the solution, also allows verification of the Eulerian structure, including the presence of logarithmic terms. Further, while the Eulerian computations broke down at the first occurrence of separation, it is found that the Lagrangian computation can be continued. It is argued that this separated solution does provide useful insight into the further evolution of the separated flow. A remarkable conclusion is that an unseparated vorticity layer at the wall, a familiar feature in unsteady separation processes, disappears in finite time.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 627-645
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    Small-scale transition in a plane mixing layer (1990)
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    Publication Date: 2011-08-19
    Description: An experimental study was conducted to investigate the generation process of random small-scale turbulence in an originally laminar mixing layer. The evolutions of the two types of deterministic structures, the spanwise and streamwise vortices, were first clarified in order to determine their roles in the transition process. A scaling rule for the streamwise distance from the trailing edge of the splitter plate to the vortex merging position was found for various velocity ratios. After this stremwise lengthscale was determined, it became clear that the spanwise wavelength of the streamwise vortices doubled after the merging of the spanwise structures which nominally doubled streamwise wavelengths. The most interesting finding was that the random small-scale eddies were produced by the interactions between the merging spanwise structures and the streamwise vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 475-500
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    On the Lagrangian description of unsteady boundary-layer separation. I - General theory (1990)
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    Publication Date: 2011-08-19
    Description: Although unsteady, high-Reynolds number, laminar boundary layers have conventionally been studied in terms of Eulerian coordinates, a Lagrangian approach may have significant analytical and computational advantages. In Lagrangian coordinates the classical boundary layer equations decouple into a momentum equation for the motion parallel to the boundary, and a hyperbolic continuity equation (essentially a conserved Jacobian) for the motion normal to the boundary. The momentum equations, plus the energy equation if the flow is compressible, can be solved independently of the continuity equation. Unsteady separation occurs when the continuity equation becomes singular as a result of touching characteristics, the condition for which can be expressed in terms of the solution of the momentum equations. The solutions to the momentum and energy equations remain regular. Asymptotic structures for a number of unsteady 3-D separating flows follow and depend on the symmetry properties of the flow. In the absence of any symmetry, the singularity structure just prior to separation is found to be quasi 2-D with a displacement thickness in the form of a crescent shaped ridge. Physically the singularities can be understood in terms of the behavior of a fluid element inside the boundary layer which contracts in a direction parallel to the boundary and expands normal to it, thus forcing the fluid above it to be ejected from the boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 210; 593-626
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    A balloon borne 19-GHz radiometer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The design and performance of a 19-GHz one-horn maser radiometer is discussed. The antenna is a lensed, conical horn with 3-deg angular resolution. The radiometer is stabilized by chopping against an internal cold load. A novel chopping scheme allows continual calibration of maser gain fluatuations with only a modest penalty in noise. The method of calibrating this instrument is described. The instrument has been used to map the sky with an equivalent blackbody temperature sensitivity of 1 mK per 3 x 3 deg resolution element.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 158-164
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    Multiple paths to subharmonic laminar breakdown in a boundary layer (1990)
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    Publication Date: 2011-08-19
    Description: Numerical simulations demonstrate that laminar breakdown in a boundary layer induced by the secondary instability of two-dimensional Tollmien-Schlichting waves to three-dimensional subharmonic disturbancews need not take the conventional lambda vortex/high-shear layer path.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 64; 641-644
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    ATLAS instrument characterization - Accuracy of the AASE and AAOE nitrous oxide data sets (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Airborne Tunabel Laser Absorption Spectrometer ATLAS was used to measure nitrous oxide in the 1987 Airborne Antarctic Ozone Experiment (AAOE) and in the 1989 Airborne Arctic Stratospheric Expedition (AASE). After the AASE, a detailed study of the ATLAS characteristics was undertaken to quantify the error inherent in the in situ measurement of atmospheric N2O. Using the latest calibration of the ATLAS (June 1989) and incorporating the recognized errors arising in the flight environment of ATLAS, it was established that, for both the AASE and the AAOE, most of the acquired N2O data sets are accurate to + or - 10 percent (2 sigma).
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 481-484
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    Time-accurate simulations of a shear layer forced at a single frequency (1990)
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 267-275
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    Analysis of stability of a planar solid-liquid interface in a dilute binary alloy (1990)
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    Publication Date: 2011-08-19
    Description: This paper reconsiders the question of stability of a planar solid-liquid interface in an undercooled alloy melt without making the restrictive assumption of no heat flow in the solid (i.e., Gs = 0). The results of this analysis indicate that, provided the thermal gradient on the solid side of the interface, Gs, is positive, stability can be achieved in an undercooled alloy melt for growth rates R greater than Ra (where Ra is the absolute stability limit of Mullins and Sekerka, 1964). Thus, the absolute stability criterion for steady-state planar growth in an undercooled alloy melt is the same as derived earlier by Mullins and Sekerka for directional solidification. Relaxing the restrictive assumption of Gs = 0 also reveals that there is a regime of stability for low growth rates and low supercoolings.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Materials Research (ISSN 0884-2914); 5; 223-228
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    Numerical experiments in supersonic boundary-layer stability (1990)
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    Publication Date: 2011-08-19
    Description: The three-dimensional (3-D) time-dependent compressible Navier-Stokes equations are numerically solved by a Fourier-Chebyshev collocation method to study the stability of supersonic flows over a flat plate. Several direct simulations carried out in this study suggest the existence of a secondary instability that might provide a route to transition. The interaction of the modes involved in the secondary instability is possibly amenable to a Floquet-type analysis. Pertinent differences between this instability and the analogous incompressible K-type secondary instability are pointed out. Some preliminary results of a 2-D direct simulation of the nonlinear evolution of a second mode perturbation wave are also discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 94-104
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    On the three-dimensional instability of strained vortices (1990)
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    Publication Date: 2011-08-19
    Description: The three-dimensional (3-D) instability of a two-dimensional (2-D) flow with elliptical streamlines has been proposed as a generic mechanism for the breakdown of many 2-D flows. A physical interpretation for the mechanism is presented together with an analytical treatment of the problem. It is shown that the stability of an elliptical flow is governed by an Ince equation. An analytical representation for a localized solution is given and establishes a direct link with previous computations and experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 76-80
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    Infrared detector responsivity measured simultaneously at multiple frequencies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The responsivity (the ratio of the output electrical signal to the incident radiation power) of an IR detector is measured at several frequencies simultaneously. A computer-controlled variable frequency chopper is used. Chopper modulation of a blackbody is square-wave-like, hence measurements can be taken not only at the fundamental frequency but also at the harmonics. The technique gives excellent agreement with the classical technique of measuring the fundamental response alone at a set of modulation frequencies. With a small enough aperture and a high enough chopper speed, agreement can be within five percent out to 31 times the fundamental frequency. The technique allows the rapid and automated acquisition of the frequency response of IR detectors, which may then be screened for responsivity, noise, and noise equivalent power.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 14
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    Unsteady heat transfer on turbine blades (1990)
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    Publication Date: 2011-08-19
    Description: This paper describes a method for calculating heat transfer on turbine blades subjected to passing wakes. It is based on the numerical solution of the boundary-layer equations for laminar, transitional, and turbulent flows with a novel procedure to account for the movement of the stagnation point. Results are presented for a model flow and show that the procedure is numerically sound and produces results that can give good agreement with measurements provided that the turbulence model is adequate.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 47-52
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    Two-dimensional convection and radiation with scattering from a Poiseuille flow (1990)
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    Publication Date: 2011-08-19
    Description: Two-dimensional combined convection and radiation heat transfer from a gray scattering fluid in a reflecting channel is considered. The model, represented by a set of simultaneous nonlinear integro-partial differential equations, is solved numerically. The effects of aspect ratio, conduction-radiation parameter, scattering albedo, and wall emissivity, are systematically investigated. It is found that these parameters have a significant influence on the temperature field and alter the radiative and convective fluxes at the hot and cold walls. In particular, when radiation effects are considerable, the heat-transfer characteristics of the fluid at the hot and cold walls are very different.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 4; 98-105
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    Elimination of spurious eigenvalues in the Chebyshev tau spectral method (1990)
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    Publication Date: 2011-08-19
    Description: A very simple modification is presented for the Chebyshev tau method which can eliminate spurious eigenvalues, proceeding from a consideration of the vorticity-streamfunction reformulation of the Chebyshev tau method and the Chebyshev-Galerkin method, which have no spurious modes. Consideration of a model problem indicates that these two approaches are equivalent, and that they reduce to the present modification of the tau method. This modified tau method also eliminates spurious eigenvalues from the Orr-Sommerfeld equation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 91; 228-239
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    Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation (1990)
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    Publication Date: 2011-08-19
    Description: The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 2147-215
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    The migration of a compound drop due to thermocapillarity (1990)
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    Publication Date: 2011-08-19
    Description: The quasistatic thermocapillary motion of a compound drop in an unbounded fluid possessing a uniform temperature gradient is analyzed. For completeness, gravitational effects are included in the treatment. The general model is formulated, and the equations for the concentric case are solved using spherical polar coordinates, while the eccentric case is handled using bispherical coordinates. Results are given for the velocity of the drop as well as that of the droplet with respect to the drop, along with useful approximations. Illustrative results are presented graphically for the thermocapillary migration of a compound drop in the special case when the droplet is a gas bubble. In addition to the velocities of the drop and the bubble, representative isotherms and streamlines also are presented which display interesting qualitative features.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 2119-213
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    Adaptive mesh generation for viscous flows using Delaunay triangulation (1990)
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    Publication Date: 2011-08-19
    Description: A method for generating an unstructured triangular mesh in two dimensions, suitable for computing high Reynolds number flows over arbitrary configurations is presented. The method is based on a Delaunay triangulation, which is performed in a locally stretched space, in order to obtain very high aspect ratio triangles in the boundary layer and the wake regions. It is shown how the method can be coupled with an unstructured Navier-Stokes solver to produce a solution adaptive mesh generation procedure for viscous flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 90; 271-291
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    A Poisson equation formulation for pressure calculations in penalty finite element models for viscous incompressible flows (1990)
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    Publication Date: 2011-08-19
    Description: The calculation of pressures when the penalty-function approximation is used in finite-element solutions of laminar incompressible flows is addressed. A Poisson equation for the pressure is formulated that involves third derivatives of the velocity field. The second derivatives appearing in the weak formulation of the Poisson equation are calculated from the C0 velocity approximation using a least-squares method. The present scheme is shown to be efficient, free of spurious oscillations, and accurate. Examples of applications are given and compared with results obtained using mixed formulations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 30; 349-361
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    The sensitivity of synthetic aperture radiometers for remote sensing applications from space (1990)
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    Publication Date: 2011-08-19
    Description: Aperture synthesis offers a means of realizing the full potential microwave remote sensing from space by helping to overcome the limitations set by antenna size. The result is a potentially lighter, more adaptable structure for applications in space. However, because the physical collecting area is reduced, the signal-to-noise ratio is also reduced and may adversely affect the radiometric sensitivity. Sensitivity is an especially critical issue for measurements from low earth orbit because the motion of the platform (about 7 km/s) limits the integration time available for forming an image. The purpose of this paper is to develop expressions for the sensitivity of remote sensing systems which use aperture synthesis. The objective is to develop basic equations general enough to be used to obtain the sensitivity of the several variations of aperture synthesis which have been proposed for sensors in space. The conventional microwave imager (a scanning total power radiometer) is treated as a special case, and the paper concludes with a comparison of three synthetic aperture configurations with the conventional imager.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Radio Science (ISSN 0048-6604); 25; 441-453
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    X-ray thin foil filters at cryogenic temperatures (1990)
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    Publication Date: 2011-08-19
    Description: The X-Ray Spectrometer (XRS), which is being developed for one of the focal plane instruments of the Advanced X-Ray Astrophysics Facility, requires filters with high X-ray transmittance, high background rejection, and operation at cryogenic temperatures. Thin foil filters can provide high X-ray transmittance and the required rejection for low-energy radiation. The results of the test program demonstrate that these filters are fully successful at cryogenic temperatures and, therefore, can provide blocking filters for the XRS with the required performance.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Engineering (ISSN 0091-3286); 29; 632-636
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    Simple analytic potentials for linear ion traps (1990)
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    Publication Date: 2011-08-19
    Description: A simple analytical model was developed for the electric and ponderomotive (trapping) potentials in linear ion traps. This model was used to calculate the required voltage drive to a mercury trap, and the result compares well with experiments. The model gives a detailed picture of the geometric shape of the trapping potential and allows an accurate calculation of the well depth. The simplicity of the model allowed an investigation of related, more exotic trap designs which may have advantages in light-collection efficiency.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Applied Physics (ISSN 0021-8979); 67; 6050-605
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    A maximum correlation method for image construction of IRAS survey data (1990)
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    Publication Date: 2011-08-19
    Description: An algorithm is presented for the construction of images using linear array data with nonuniform scan coverage of object space and nonuniform detector responses. The algorithm achieves the maximum correlation between adjacent pixels, i.e., the smoothest image, consistent with the data and data uncertainties. For high spatial data density and signal-to-noise ratio, the achievable spatial resolution can exceed the diffraction limit of the optics. The capability of the algorithm is illustrated using 60-micron data from the region centered on the galaxy M101, obtained during the all-sky survey performed by the Infrared Astronomical Satellite. The 60-micron map produced has a resolution of about 36 arcsec and allows the identification of many H II regions by position and aperture photometry for the brighter ones. The achieved resolution is discussed in terms of the a priori estimate of the mean correlation length of the data, the directly measured FWHM in the final image, and the results of aperture photometry of M101 H II regions NGC 5447, 5455, 5461, 5462 and 5471.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1674-168
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    The baroeffect and an appropriate momentum boundary condition (1990)
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    Publication Date: 2011-08-19
    Description: As disparate molecular weight gases isothermally diffuse between two ends of a capillary tube, they can support a pressure gradient. The magnitude of this pressure gradient depends critically on viscous wall stress and becomes a measure of the boundary condition. Here, a one-dimensional analytical model is proposed that allows for specular gas reflection from the wall. It explains anomalous (4/3) correction factors required previously to match experiment to baroeffect models. It predicts a new physical phenomenon, a surface-driven baroeffect for equal molecular weight gases. Diffusive slip contributions exceed the order of convective diffusion for Peclet number Pe less than 1 and approximately equal convective diffusion for Pe values between 1 and 4. For binary gases, this model further extends the baroeffect experiment as a means to find momentum accommodation coefficients, slip lengths, and external friction coefficients. A corrected binary diffusion coefficient is defined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 858-865
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  • 91
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    Effect of a crystal-melt interface on Taylor-vortex flow (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 700-705
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  • 92
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    Hydrodynamic interactions in directional solidification (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A binary liquid undergoes unidirectional solidification. The one-dimensional steady state is susceptible to morphological instability that causes the solid/liquid interface to change from a planar state to a cellular pattern. This paper examines the effects on this transition of volume-change convection, buoyancy-driven convection or forced flows. It emphasizes how flows alter stability limits, create scale and pattern changes in morphology, and create, through coupling, new instabilities. Emphasis is placed on the physical mechanisms of the interactions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 212; 241-262
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  • 93
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    Preliminary drop-tower experiments on liquid-interface geometry in partially filled containers at zero gravity (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Plexiglass containers with rounded trapezoidal cross sections were designed and built to test the validity of Concus and Finn's existence theorem (1974, 1983) for a bounded free liquid surface at zero gravity. Experiments were carried out at the NASA Lewis two-second drop tower. Dyed ethanol-water solutions and three immiscible liquid pairs, with one liquid dyed, were tested. High-speed movies were used to record the liquid motion. Liquid rose to the top of the smaller end of the containers when the contact angle was small enough, in agreement with the theory. Liquid interface motion demonstrated a strong dependence on physical properties, including surface roughness and contamination.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Experiments in Fluids (ISSN 0723-4864); 8; 6, Ma; 312-318
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  • 94
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    A contribution toward rational modeling of the pressure-strain-rate correlation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A novel method of obtaining an analytical expression of the 'linear part' of the pressure-strain-rate tensor in terms of the anisotropy tensor of the Reynolds stresses has been developed, where the coefficients of the seven independent tensor terms are functions of the invariants of the Reynolds-stress anisotropy. The coefficients are evaluated up to fourth order in the anisotropy of the Reynolds stresses to provide guidance for development of a turbulence model.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 630-633
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  • 95
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    Control of turbulent separated flow over a rearward-facing ramp using longitudinal grooves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 283-285
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  • 96
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    Rotational-translational energy transfer in rarefied nonequilibrium flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new model for simulating the transfer of energy between the translational and rotational modes is derived for a homogeneous gas of diatomic molecules. The model has been developed specifically for use in discrete particle simulation methods where molecular motion and intermolecular collisions are treated at the molecular level. A temperature dependence is introduced which has been predicted by theory and observed in experiment. The new model is applied to the relaxation of rotational temperature, and is found to produce significant differences in comparison with the model normally employed at both high and low temperatures. Calculations have also been performed for a Mach 7 normal shock wave.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 2; 447-452
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  • 97
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    Parallel flows with Soret effect in tilted cylinders (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Henry and Roux (1986, 1987, 1988) have conducted extensive numerical studies on the interaction of Soret separation with convection in cylindrical geometry. Many of their solutions exhibit parallel flow away from end walls. Their parallel flow results can be matched by closed-form solutions. Solutions are nonunique in some parameter regions. Disappearance of one branch of solutions correlates with a sudden transition of Henry and Roux's results from a separated to a well-mixed flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 211; 355-372
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  • 98
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    Theoretical study of turbulent channel flow - Bulk properties, pressure fluctuations, and propagation of electromagnetic waves (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper, we apply two theoretical turbulence models, DIA and the recent GISS model, to study properties of a turbulent channel flow. Both models provide a turbulent kinetic energy spectral function E(k) as the solution of a non-linear equation; the two models employ the same source function but different closures. The source function is characterized by a rate n sub s (k) which is derived from the complex eigenvalues of the Orr-Sommerfeld (OS) equation in which the basic flow is taken to be of a Poiseuille type. The O-S equation is solved for a variety of Reynolds numbers corresponding to available experimental data. A physical argument is presented whereby the central line velocity characterizing the basic flow, U0 sup L, is not to be identified with the U0 appearing in the experimental Reynolds number. The theoretical results are compared with two types of experimental data: (1) turbulence bulk properties, and (2) properties that depend strongly on the structure of the turbulence spectrum at low wave numbers. The only existing analytical expression for Pi (k) cannot be used in the present case because it applies to the case of a flat plate, not a finite channel.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 211; 1-35
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  • 99
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    Splitting of inviscid fluxes for real gases (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Flux-vector and flux-difference splittings for the inviscid terms of the compressible flow equations are derived under the assumption of a general equation of state for a real gas in equilibrium. No necessary assumptions, approximations for auxiliary quantities are introduced. The formulas derived include several particular cases known for ideal gases and readily apply to curvilinear coordinates. Applications of the formulas in a TVD algorithm to one-dimensional shock-tube and nozzle problems show their quality and robustness.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 87; 1-24
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  • 100
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    Improvement of pump tubes for gas guns and shock tube drivers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In a pump tube, a gas is mechanically compressed, producing very high pressures and sound speeds. The intensely heated gas produced in such a tube can be used to drive light gas guns and shock tubes. Three concepts are presented that have the potential to allow substantial reductions in the size and mass of the pump tube to be achieved. The first concept involves the use of one or more diaphragms in the pump tube, thus replacing a single compression process by multiple, successive compressions. The second concept involves a radical reduction in the length-to-diameter ratio of the pump tube and the pump tube piston. The third concept involves shock heating of the working gas by high explosives in a cyclindrical geometry reusable device. Preliminary design analyses are performed on all three concepts and they appear to be quite feasible. Reductions in the length and mass of the pump tube by factors up to about 11 and about 7, respectively, are predicted, relative to a benchmark conventional pump tube.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 28; 483-491
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