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  • 1
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    Six-beam models in radiative transfer theory (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A critical analysis is given of the applicability of six-beam models to radiative transfer in particulate materials. The method of introducing transverse scattering in these models is shown to cause fundamental difficulties in the case of physically plausible phase functions; in particular, the effective absorptivity is abnormally large and thus results in incorrect reflectances and transmittances. Six-beam calculations for several media are compared with accurate solutions, with Chu-Churchill two-beam results, and with a simple modification to the Eddington approximation, the last being generally superior over a wide range of conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Applied Optics; 15; Dec. 197
    Format: text
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  • 2
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    Experimental study of a free turbulent shear flow at Mach 19 with electron-beam and conventional probes (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An experimental study of the initial development region of a hypersonic turbulent free mixing layer was made. Data were obtained at three stations downstream of a M = 19 nozzle over a Reynolds range of 1.3 million to 3.3 million per meter and at a total temperature of about 1670 K. In general, good agreement was obtained between electron-beam and conventional probe measurements of local mean flow parameters. Measurements of fluctuating density indicated that peak root-mean-square (rms) levels are higher in the turbulent free mixing layer than in boundary layers for Mach numbers less than 9. The intensity of rms density fluctuations in the free stream is similar in magnitude to pressure fluctuations in high Mach number flows. Spectrum analyses of the measured fluctuating density through the shear layer indicate significant fluctuation energy at the lower frequencies (0.2 to 5 kHZ) which correspond to large-scale disturbances in the high-velocity region of the shear layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TN-D-7981 , L-10138
    Format: application/pdf
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  • 3
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    Modeling of three-dimensional mixing and reacting ducted flows (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A computer code, based upon a finite element solution algorithm, was developed to solve the governing equations for three-dimensional, reacting boundary region, and constant area ducted flow fields. Effective diffusion coefficients are employed to allow analyses of turbulent, transitional or laminar flows. The code was used to investigate mixing and reacting hydrogen jets injected from multiple orifices, transverse and parallel to a supersonic air stream. Computational results provide a three-dimensional description of velocity, temperature, and species-concentration fields downstream of injection. Experimental data for eight cases covering different injection conditions and geometries were modeled using mixing length theory (MLT). These results were used as a baseline for examining the relative merits of other mixing models. Calculations were made using a two-equation turbulence model (k+d) and comparisons were made between experiment and mixing length theory predictions. The k+d model shows only a slight improvement in predictive capability over MLT. Results of an examination of the effect of tensorial transport coefficients on mass and momentum field distribution are also presented. Solutions demonstrating the ability of the code to model ducted flows and parallel strut injection are presented and discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-2661
    Format: application/pdf
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  • 4
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    Pressure- and buoyancy-driven thermal convection in a rectangular enclosure (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Results are presented for unsteady laminar thermal convection in compressible fluids at various reduced levels of gravity in a rectangular enclosure which is heated on one side and cooled on the opposite side. The results were obtained by solving numerically the equations of conservation for a viscous, compressible, heat-conducting, ideal gas in the presence of a gravitational body force. The formulation differs from the Boussinesq simplification in that the effects of variable density are completely retained. A conservative, explicit, time-dependent, finite-difference technique was used and good agreement was found for the limited cases where direct comparison with previous investigations was possible. The solutions show that the thermally induced motion is acoustic in nature at low levels of gravity and that the unsteady-state rate of heat transfer is thereby greatly enhanced relative to pure conduction. The nonlinear variable density profile skews the streamlines towards the cooler walls but is shown to have little effect on the steady-state isotherms.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 70; Aug. 26
    Format: text
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  • 5
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    A three-dimensional turbulent compressible flow model for ejector and fluted mixers (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A three dimensional finite element computer code was developed to analyze ejector and axisymmetric fluted mixer systems whose flow fields are not significantly influenced by streamwise diffusion effects. A two equation turbulence model was used to make comparisons between theory and data for various flow fields which are components of the ejector system, i.e., (1) turbulent boundary layer in a duct; (2) rectangular nozzle (free jet); (3) axisymmetric nozzle (free jet); (4) hypermixing nozzle (free jet); and (5) plane wall jet. Likewise, comparisons of the code with analytical results and/or other numerical solutions were made for components of the axisymmetric fluted mixer system. These included: (1) developing pipe flow; (2) developing flow in an annular pipe; (3) developing flow in an axisymmetric pipe with conical center body and no fluting and (4) developing fluted pipe flow. Finally, two demonstration cases are presented which show the code's ability to analyze both the ejector and axisymmetric fluted mixers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-159467
    Format: application/pdf
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  • 6
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    Swirling flow of a dissociated gas (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Most physical applications of the swirling flow, defined as a vortex superimposed on an axial flow in the nozzle, involve high temperatures and the possibility of real gas effects. The generalized one-dimensional swirling flow in a converging-diverging nozzle is analyzed for equilibrium and frozen dissociation using the ideal dissociating gas model. Numerical results are provided to illustrate the major effects and to compare with results obtained for a perfect gas with constant ratio of specific heats. It is found that, even in the case of real gases, perfect gas calculations can give a good estimate of the reduction in mass flow due to swirl.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 7
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    A study of viscous cross-flow effects on circular cylinders at high Reynolds numbers (1979)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Results of experimental studies on viscous cross-flow over circular cylinders for Reynolds numbers from 0.15 x 10 to the 6th to 10.9 x 10 to the 6th at Mach numbers of less than 0.3 are presented and compared with previous work where possible. Results presented include the variation of static cross-flow drag coefficients with both Reynolds number and ratio of surface roughness to model diameter, the variation of Strouhal number with Reynolds number and the dynamic variation of surface static pressure coefficients with both angular position around the cylinder and Reynolds number. The effects of end-plates on flow around two-dimensional bluff-bodies and of tunnel blockage on drag measurements are also discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 79-1477 , American Institute of Aeronautics and Astronautics, Fluid and Plasma Dynamics Conference; Jul 23, 1979 - Jul 25, 1979; Williamsburg, VA
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  • 8
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    Re-entrant groove heat pipe (1977)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper describes theoretical and experimentally verified heat pipe characteristics of an axially grooved aluminum extrusion with a re-entrant groove profile. The extrusion is 13 mm diameter with 20 axial grooves, each groove consisting of a nominal .8 mm diameter channel with a .2 mm wide passageway connecting the channel to the hollow core. A computer program was written to compute the zero gravity heat transport capability of the extrusion. A heat pipe was fabricated and its performance characteristics measured. The characteristics of the pipe with ammonia at 20 C are: zero gravity pumping limit 143 w-meters; static wicking height 21.5 mm; evaporator and condenser coefficients 7300 and 20,500 watt/sq m C, respectively.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 77-773 , Thermophysics Conference; Jun 27, 1977 - Jun 29, 1977; Albuquerque, NM
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  • 9
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    Pressure and heat-transfer distributions in a simulated wing-elevon cove with variable leakage at a free-stream Mach number of 6.9 (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An experimental aerodynamic heating investigation was conducted to determine effects of hot boundary-layer ingestion into the cove on the windward surface between a wing and elevon for cove seal leak areas nominally between 0 and 100 percent of cove entrance area. Pressure and heating-rate distributions were obtained on the wing and elevon surfaces and on the cove walls of a full-scale model that represented a section of the cove region on the space shuttle orbiter. Data were obtained for both attached and separated turbulent boundary layers upstream of the unswept cove entrance. Average free-stream Mach number was 6.9, average free-stream unit Reynolds numbers were 1.31 x 10 to the 6th power and 4.40 x 10 to the 6th power per meter (0.40 x 10 to the 6th power and 1.34 x 10 to the 6th power per foot), and average total temperature was 1888 K (3400 R). Cove pressures and heating rates varied as a function of seal leak area independent of leak aspect ratio. Although cove heating rates for attached flow did not appear intolerable, it was postulated that convective heating in the cove may increase with time. For separated flow, the cove environment was considered too severe for unprotected interior structures of control surfaces.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-74095 , L-12591
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  • 10
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    Numerical solutions and laser-Doppler measurements of spin-up (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The spin-up flow in a cylinder of homogeneous fluid has been examined both experimentally and numerically. A series of laser-Doppler measurements was made of the zonal flow over a range of Ekman numbers and Rossby numbers at various locations in the interior of the flow. These measurements exceed previous ones in accuracy. The weak inertial modes excited by the impulsive start are detectable. The numerical simulations used the primitive equations in axisymmetric form and employed finite-difference techniques on both constant and variable grids. The number of grid points necessary to resolve the Ekman layers was determined. A thorough comparison of the simulations and the experimental measurements is made which includes the details of the amplitude and frequency of the inertial modes. Agreement to within the experimental tolerance is achieved. Analytical results for conditions identical to those in the experiments are not available but some similar linear and nonlinear theories are also compared with the experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 85; Apr. 27
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