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  • FLUID MECHANICS AND HEAT TRANSFER  (189)
  • 1990-1994  (189)
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  • 1992  (95)
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  • 1990-1994  (189)
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  • 1
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    Some effects of swirl on turbulent mixing layer development (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-12
    Beschreibung: Effects of swirl on the development of an axisymmetric turbulent mixing layer have been studied. The development of the zero swirl case is found to be consistent with that of a single-stream mixing layer developing from a tripped boundary layer. In particular, the consistency of the measured stress levels shows the accuracy of the measurement system. Swirl increases all the Reynolds stress levels with the increased scaling with swirl number. The shear stresses are found to be affected significantly more than the normal stresses. The stress increases are partly explained by considering extra production terms in the transport equations that are activated by the presense of the swirl. The thickness and growth rate for the lower swirl rate are found to be comparable to the zero swirl case, while those for the higher swirl rate are increased significantly, in line with the increased Reynolds stresses.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Physics of Fluids A (ISSN 0899-8213); 3; 2716-272
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 2
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    Studies of the effects of curvature on dilution jet mixing (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: An analytical program was conducted using both three-dimensional numerical and empirical models to investigate the effects of transition liner curvature on the mixing of jets injected into a confined crossflow. The numerical code is of the TEACH type with hybrid numerics; it uses the power-law and SIMPLER algorithms, an orthogonal curvilinear coordinate system, and an algebraic Reynolds stress turbulence model. From the results of the numerical calculations, an existing empirical model for the temperature field downstream of single and multiple rows of jets injected into a straight rectangular duct was extended to model the effects of curvature. Temperature distributions, calculated with both the numerical and empirical models, are presented to show the effects of radius of curvature and inner and outer wall injection for single and opposed rows of cool dilution jets injected into a hot mainstream flow.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Journal of Propulsion and Power (ISSN 0748-4658); 8; 209-218
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Experimental study of cross-stream mixing in a cylindrical duct (1991)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: An experimental investigation of cross stream injection and mixing has been conducted with application to a low NO(x) combustor for the HSCT. Mixing in a cylindrical chamber has been studied for transverse injection from slanted slot and round orifice injectors. Momentum ratio, density ratio, and injector geometry were the primary variables. Slanted slots of various size, aspect ratio, and number were studied. Quantitative measurement of injectant concentration distributions were obtained by planar digital imaging of the Mie-scattered light from an aerosol seed uniformly mixed with the injectant. The unmixedness, defined as the ratio of the rms concentration fluctuation to mean concentration in a plane perpendicular to the main flow direction, was found to be primarily a function of momentum ratio and injector spacing. An optimum spacing is indicated. Unmixedness is also a function of orifice size, or mass flow ratio, but the mass flow dependence can be accounted for by normalizing the unmixedness with its maximum theoretical value. The data indicate that density ratio greater than unity retards mixing. It was found that above a certain momentum flux ratio, mixing with slanted slot injectors was better than with round hole injectors.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 91-2459
    Format: text
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  • 4
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    Numerical analysis of rarefied slit flows. II - Navier-Stokes simulations (1991)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: The model problem of pressure-driven flow of a rarefied monatomic gas through a two-dimensional slit is analyzed via full Navier-Stokes numerical simulation. Parametric solutions are generated for slit-height based Knudsen number ranging from continuum to transitional flow and for reservoir pressure ratios leading to subsonic and supersonic flow. The change in the structure of the flowfield near the slit as a function of pressure ratio and Knudsen number are quantified from a purely continuum standpoint. The choice of numerical domain size, boundary conditions and treatment of the slit are also discussed. As expected, comparison with a Direct Simulation Monte Carlo solution for a highly rarefied case shows large differences in the predicted mass flow. The cause of these differences can be quantified through detailed comparison of the local flowfield properties. For the larger pressure ratio cases qualitative trends with increasing rarefaction are discussed, including the change in the sonic line shape in the slit and the in total mass flow.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 91-1748
    Format: text
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  • 5
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    Computational methodology for radiation heat transfer in the flowfield of an AOTV (1991)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A computational methodology is developed for the calculation of radiation heat transfer in a non-scattering medium where nonequilibrium conditions exist and give rise to complex spectra. The specific problem of radiation in an aeroassisted orbital transfer vehicle (AOTV) flowfield is addressed. Nonequilibrium radiation from the gases around a hypersonic vehicle is evaluated using the NASA-Ames NEQAIR program together with a three-dimensional geometrical flowfield model. Nonequilibrium compositions and temperatures are taken from NASA-Langley 3-D hypersonic flowfield calculations that include real-gas effects and finite-rate chemical kinetics. It is shown that the concept of a transmission path adjustment, together with precomputations of curves of growth based upon local properties at flowfield locations, facilitates radiation calculations. Sample calculations of directional and spectral distributions of gas radiation received upon a hypersonic vehicle are presented.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 91-1407
    Format: text
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  • 6
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    The design/analysis of flows through turbomachinery - A viscous/inviscid approach (1991)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: A new design/analysis system for the flows through turbomachinery is currently being developed for studying turbomachinery problems with an axisymmetric viscous/inviscid 'average-passage' throughflow code. The advantage of this approach, compared to streamline curvature codes, is that the solutions obtained simulate some of the unsteadiness, compressibility and viscous effects of a multistage turbomachine. The design/analysis system consists of three elemental parts, the axisymmetric block grid generator, the blade surface element code, and the axisymmetric flow code. Each element of the system will be discussed and the flow solutions for three axisymmetric geometries will be shown compared to experimental data where available. The computations are shown to be in very good agreement with test data for SR7 spinner body and transonic boattail geometry obtained in the wind tunnels at NASA Lewis Research Center. The VIADAC Rotor 67 Fan results were compared to PARC2D calculated results and shown to be in very good agreement.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 91-2010
    Format: text
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  • 7
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    Effects of turbulence and number density on the drag coefficient of droplets (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Droplet drag coefficients for polydispersed drops are determined via the behavior of drops decelerating on the stagnation streamline of a cylinder with an afterbody mounted in a wind tunnel test section. A variety of velocity, turbulence levels, and droplet number densities were studied. A force balance equation technique was used to determine drag coefficient. For the levels of number density, up to 700/cc, and turbulence, up to about 7 percent, no definite effects were seen. However, the smallest drops in the high turbulence case showed some evidence of drop-turbulence and/or drop-drop interactions. The drag results that were developed for this set of measurements agreed well with other empirical relations previously determined.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 91-0074
    Format: text
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  • 8
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    Navier-Stokes solutions with surface catalysis for Martian atmospheric entry (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: In this study numerical solutions have been obtained for two-dimensional axisymmetric hypersonic nonequilibrium CO2 flow over a high angle blunt cone with appropriate surface boundary conditions to account for energy and mass conservation at the body surface. The flowfield is described by the Navier-Stokes equations and multicomponent conservation laws which account for both translational and internal vibrational nonequilibrium effects. Complete forebody solutions have been obtained for the peak heating point of the Mars entry trajectory specified in the proposed NASA MESUR (Mars Environmental Survey) project. In these solutions, radiative equilibrium wall temperature and surface heating distributions are determined over the MESUR aeroshell forebody for entry velocity equal to 7 km/sec with varying degrees of surface catalysis. The effects of gas kinetics, surface catalysis, transport properties, and vibrational relaxation times on the surface heating are examined. The results identify some important issues in the prediction of surface heating for flows in thermochemical nonequilibrium and show that the Navier-Stokes code used herein is effective for thermal protection system design and materials selection.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 92-2946
    Format: text
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  • 9
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    A comparative study of scramjet injection strategies for high Mach numbers flows (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A simple method for predicting the axial distribution of supersonic combustor thrust potential is described. A complementary technique for illustrating the spatial evolution and distribution of thrust potential and loss mechanisms in reacting flows is developed. Wall jet cases and swept ramp injector cases for Mach 17 and Mach 13.5 flight enthalpy inflow conditions are numerically modeled and analyzed using these techniques. The visualization of thrust potential in the combustor for the various cases examined provides a unique tool for increasing understanding of supersonic combustor performance potential.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 92-3287
    Format: text
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  • 10
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    Linear-stability theory of thermocapillary convection in a model of float-zone crystal growth (1992)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Linear-stability theory has been applied to a basic state of thermocapillary convection in a model half-zone to determine values of the Marangoni number above which instability is guaranteed. The basic state must be determined numerically since the half-zone is of finite, O(1) aspect ratio with two-dimensional flow and temperature fields. This, in turn, means that the governing equations for disturbance quantities will remain partial differential equations. The disturbance equations are treated by a staggered-grid discretization scheme. Results are presented for a variety of parameters of interest in the problem, including both terrestrial and microgravity cases.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIAA PAPER 92-0604
    Format: text
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