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  • 1
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    Thermal convection during Bridgman crystal growth (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Numerical experiments are used to study thermally driven flows which occur during vertical Bridgman crystal growth of a single component fluid. The solid-liquid interface was specified as parabolic and flow patterns were calculated for various insulation thicknesses, Grashof, Prandtl, and Biot numbers. When the melt is on top and the gravity vector is axially downward it is shown that flow persists as long as a radial temperature gradient is present. If the interface is convex, as viewed from the liquid, a single cell is observed. A concave interface exhibits multiple counterrotating cells. The insulation thickness and Grashof, Prandtl, and Biot numbers influence the flow in a quantitative manner.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Crystal Growth (ISSN 0022-0248); 68; 747-756
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  • 2
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    Computational fluid dynamics in a marine environment (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The introduction of the supercomputer and recent advances in both Reynolds averaged, and large eddy simulation fluid flow approximation techniques to the Navier-Stokes equations, have created a robust environment for the exploration of problems of interest to the Navy in general, and the Naval Underwater Systems Center in particular. The nature of problems that are of interest, and the type of resources needed for their solution are addressed. The goal is to achieve a good engineering solution to the fluid-structure interaction problem. It is appropriate to indicate that a paper by D. Champman played a major role in developing the interest in the approach discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Ames Research Center, Supercomputing in Aerospace; p 183-185
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  • 3
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    Implementation of a vibrationally linked chemical reaction model for DSMC (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-109109 , NAS 1.15:109109
    Format: application/pdf
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  • 4
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    Radiation modeling with direct simulation Monte Carlo (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Improvements in the modeling of radiation in low density shock waves with direct simulation Monte Carlo (DSMC) are the subject of this study. A new scheme to determine the relaxation collision numbers for excitation of electronic states is proposed. This scheme attempts to move the DSMC programs toward a more detailed modeling of the physics and more reliance on available experimental data. The new method is compared with the current modeling technique and both techniques are compared with available data. The differences in the results are evaluated. The test case is based on an AVCO-Everett shock tube experiment, a 10-km/s standing shock wave in air at 0.1 Torr. The new method agrees with the available data as well as the results from the earlier scheme and is more easily extrapolated to different flow conditions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-1409
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  • 5
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    Monte Carlo simulation of a near-continuum shock-shock interaction problem (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A complex shock interaction is calculated with direct simulation Monte Carlo (DSMC). The calculation is performed for the near-continuum flow produced when an incident shock impinges on the bow shock of a 0.1 in. radius cowl lip for freestream conditions of approximately Mach 15 and 35 km altitude. Solutions are presented both for a full finite-rate chemistry calculation and for a case with chemical reactions suppressed. In each case, both the undisturbed flow about the cowl lip and the full shock interaction flowfields are calculated. Good agreement has been obtained between the no-chemistry simulation of the undisturbed flow and a perfect gas solution obtained with the viscous shock-layer method. Large differences in calculated surface properties when different chemical models are used demonstrate the necessity of adequately representing the chemistry when making surface property predictions. Preliminary grid refinement studies make it possible to estimate the accuracy of the solutions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 92-2862
    Format: text
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  • 6
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    Solar dynamic heat rejection technology. Task 1: System concept development (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results are presented of a concept development study of heat rejection systems for Space Station solar dynamic power systems. The heat rejection concepts are based on recent developments in high thermal transport capacity heat pipe radiators. The thermal performance and weights of each of the heat rejection subsystems is addressed in detail, and critical technologies which require development tests and evaluation for successful demonstration are assessed and identified. Baseline and several alternate heat rejection system configurations and optimum designs are developed for both Brayton and Rankine cycles. The thermal performance, mass properties, assembly requirements, reliability, maintenance requirements and life cycle cost are determined for each configuration. A specific design was then selected for each configuration which represents an optimum design for that configuration. The final recommendations of heat rejection system configuration for either the Brayton or Rankine cycles depend on the priorities established for the evaluation criteria.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-179618 , NAS 1.26:179618
    Format: application/pdf
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  • 7
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    Approximations for hypervelocity nonequilibrium radiating, reacting, and conducting stagnation regions (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An approximate solution which includes the effects of chemical and thermal nonequilibrium and nonequilibrium nongray radiative transfer and which is suitable for rapidly obtaining approximate solutions for flowfield structure and estimates of radiative heat transfer is presented. Comparisons are made with Fire 2 data and example applications to a hypothetical Mars return AOTV are presented. Parametric results indicate that further studies of VUV processes and radiation models are needed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 88-2672
    Format: text
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  • 8
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    Comparison of vibration dissociation coupling and radiative heat transfer models for AOTV/AFE flowfields (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A series of detailed studies comparing various vibration dissociation coupling models, reaction systems and rates, and radiative heating models has been conducted for the nonequilibrium stagnation region of an AFE/AOTV vehicle. Atomic and molecular nonequilibrium radiation correction factors have been developed and applied to various absorption coefficient step models, and a modified vibration dissociation coupling model has been shown to yield good vibration/electronic temperature and concentration profiles. While results indicate sensitivity to the choice of vibration dissociation coupling model and to the nitrogen electron impact ionization rate, by proper combinations accurate flowfield and radiative heating results can be obtained. These results indicate that nonequilibrium effects significantly affect the flowfield and the radiative heat transfer. However, additional work is needed in ionization chemistry and absorption coefficient modeling.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 88-2673
    Format: text
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  • 9
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    High thermal-transport capacity heat pipes for space radiators (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper presents the results of performance tests of several dual-slot heat pipe test articles. The dual-slot configuration has a very high thermal transport capability and has been identified as a very promising candidate for the radiator system for the NASA Space Station solar dynamic power modules. Two six-foot long aluminum heat pipes were built and tested with ammonia and acetone. A 20-ft long heat pipe was also built and tested with ammonia. The test results have been compared with performance predictions. A thermal transport capacity of 2000 W at an adverse tilt of 1 in. and a 1000 W capacity at an adverse tilt of 2 in. were achieved on the 20-ft long heat pipe. These values are in close agreement with the predicted performance limits.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: SAE PAPER 871509
    Format: text
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  • 10
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    Nonequilibrium chemical and radiation coupling phenomena in AOTV flowfields (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A flowfield model for the nonequilibrium stagnation region of high altitude entry vehicles which includes nonequilibrium chemistry, multitemperature, viscous, conduction, and diffusion effects is presented. It contains coupled nongray nonequilibrium radiative transfer for atoms and molecules and local thermodynamic nonequilibrium phenomena. Comparison with Fire 2 flight data verifies that the model is reasonably accurate; and it has been applied to two AFE trajectory points, a high speed return from Mars, a series of points at 80 km for 12 to 16 km/sec, and three altitudes at 16 km/sec. Based on these results shock slip is significant, radiation cooling/coupling is minor at AFE conditions but important by 14 km/sec and dominant at 16 km/sec, radiation for the AFE is small but important and primarily molecular, above 12 km/sec atomic radiation is a significant or dominant portion of the total heating, and local thermodynamic nonequilibrium is important and should be included in all models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-0569
    Format: text
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