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  • 11
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    Effect of low Reynolds number turbulence amplification on the Galileo probe flowfield (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The amplification of turbulence at low Reynolds numbers is analyzed as it affects the Jupiter-entry flowfield, surface-heating rate, and mass-loss rate of the 335-kg Galileo probe now being designed. The constant k(2) in the Clauser-Klebanoff outer law of the two-layer algebraic eddy-viscosity model of Cebeci (1970), as used in earlier models of the Galileo flowfield (Moss and Simmonds, 1982), is modified to increase at low Reynolds numbers, as found experimentally by Varner and Adams (1980). Calculations were performed for peak heating conditions (at 49.13 sec of entry), using a turbulent Prandtl number of 0.9 and turbulent Lewis numbers (LeT) of 0.8, 1.0, and 1.2. The low-Reynolds-number effect is found to produce mass-loss-ratio increases of from 4 to 50 percent, while an LeT of 1.2 produced an increase of from 4 to 10 percent as compared to an LeT of 1.0. While these findings are based on experimental data obtained under conditions somewhat different from those probably present on Jupiter, their importance for a conservative probe design is stressed.
    Keywords: ASTRODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4560); 20; July-Aug
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  • 12
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    A comparative study of time-marching and space-marching numerical methods (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Menees (1981) has conducted an evaluation of three different flowfield codes for the Jupiter entry conditions. However, a comparison of the codes has been made difficult by the fact that the three codes use different solution procedures, different computational mesh sizes, and a different convergence criterion. There are also other differences. For an objective evaluation of the different numerical solution methods employed by the codes, it would be desirable to select a simple no-blowing perfect-gas flowfield case for which the turbulent models are well established. The present investigation is concerned with the results of such a study. It is found that the choice of the numerical method is rather problem dependent. The time-marching and the space-marching method provide both comparable results if care is taken in selecting the appropriate mesh size near the body surface.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal; 21; Jan. 198
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  • 13
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    Convective and radiative heating of a Saturn entry probe (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The extent of convective and radiative heating for a Saturn entry probe is investigated in the absence and presence of ablation mass injection. The flow in the shock layer is assumed to be axisymmetric, viscous and in local thermodynamic equilibrium. The importance of chemical nonequilibrium effects for both the radiative and convective nonblowing surface heating rates is demonstrated for prescribed entry conditions. Results indicate that the nonequilibrium chemistry can significantly influence the rate of radiative heating to the entry probes. With coupled carbon-phenolic ablation injection, the convective heating rates are reduced substantially. Turbulence has little effect on radiative heating but it increases the convective heating considerably.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 27; 191-205
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  • 14
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    Thermophysical aspects of re-entry flows (1986)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: The present conference discusses low density aerothermodynamics, the drag of bodies in rarefied hypersonic flow, transitional hypervelocity aerodynamic simulation and scaling, high temperature kinetics and transport properties, electron-nitrogen molecule collisions in high temperature nonequilibrium air, theoretical studies of dissociative recombination, the transport properties of some atom/ion interactions in air, and the interaction energies, dipole transition moments, and transport cross sections of N(+)-N and O(+)-O. Also discussed are the results of studies of potential fluid mechanisms for enhanced stagnation heating, vortex-induced leeward heating on a biconic at Mach 6 and 10, the effects of surface discontinuities on convective heat transfer in hypersonic flow, computational convergence in chemical reacting flows, and three-dimensional viscous shock layer applications for the Space Shuttle Orbiter.
    Keywords: AERODYNAMICS
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  • 15
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    DSMC Simulation of Shock/Shock Interactions: Emphasis on Type IV Interactions (1999)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: This paper presents the results of a numerical study of shock/shock interactions that include both the Edney type IV and type III interactions, with emphasis on the type IV interactions. Computations are made using the direct simulation Monte Carlo (DSMC) method of Bird for Mach 10 air flow, as produced in the ONERA R5Ch low-density wind tunnel. The simulations include the flow about a shock generator which creates a relatively weak oblique shock that impinges on a much stronger cylinder bow shock. The sensitivity and characteristics of the interactions are examined by varying the horizontal distance separating the shock generator leading edge and cylinder. Results of the simulation for one separation distance are compared with wind tunnel measurements. Comparisons are made for surface heating and pressure and for flow-field values of density and rotational temperatures, as obtained with the Dual-line Coherent Anti-Stokes Scattering (DL-CARS) technique. The comparisons between experiment and calculation yield a consistent description of the shock interaction features and a consistent description of the surface heating and pressure distributions, with the exception of the peak values-the computed values being greater than the measured values.
    Keywords: Fluid Mechanics and Thermodynamics
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  • 16
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    Energetics of gas-surface interactions in transitional flows at entry velocities (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The direct simulation Monte Carlo (DSMC) method has been used to calculate the molecular velocity and energy distributions of molecules striking a surface after traversing a shock layer in hypersonic transitional flow. The calculations were performed for a 1.6-m-diameter sphere at a nominal velocity for re-entry of 7.5 km/s over an altitude range of 130 to 90 km. Real gas effects and chemical reactions were included in the DSMC simulations. Results are presented for these conditions and the need for gas-surface interaction experiments is discussed.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-1338
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  • 17
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    Direct simulation of hypersonic flows over blunt slender bodies (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results of a numerical study of low-density hypersonic flow about cylindrically blunted wedges and spherically blunted cones with body half angles of 0, 5, and 10 deg are presented. Most of the transitional flow regime encountered during entry between the free molecule and continuum regimes is simulated for a reentry velocity of 7.5 km/s by including freestream conditions of 70 to 100 km. The bodies are at zero angle of incidence and have diffuse and finite catalytic surfaces. Translational, thermodynamic, and chemical nonequilibrium effects are considered in the numerical simulation by utilizing the direct simulation Monte Carlo (DSMC) method. The numerical simulations show that noncontinuum effects such as surface temperature jump, and velocity slip are evident for all cases considered. The onset of chemical dissociation occurs at a simulated altitude of 96 km for the two-dimensional configurations. Comparisons between the DSMC and continuum viscous shock-layer calculations highlight the significant difference in flowfield structure predicted by the two methods.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1348
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  • 18
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    Slip-boundary equations for multicomponent nonequilibrium airflow (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Equations are presented for the surface-slip (or jump) values of species concentration, pressure, velocity, and temperature in the low Reynolds number, high-altitude flight regime of a space vehicle. These are obtained from closed-form solutions of the mass, momentum, and energy flux equations by using the Chapman-Enskog velocity distribution function. This function represents a solution of the Boltzmann equation in the Navier-Stokes approximation. The analysis, obtained for nonequilibrium multicomponent airflow, includes the finite-rare surface catalytic recombination and changes in the internal energy during reflection from the surface. Expressions for the various slip quantities have been obtained in a form which can readily be employed in flow-field computations. A consistent set of equations is provided for multicomponent and binary mixtures and single-species gas. An expression is also provided for the finite-rate species-concentration boundary condition for a multicomponent mixture in the absence of slip.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TP-2452 , L-15952 , NAS 1.60:2452
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  • 19
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    Direct simulation of hypersonic transitional flow (1986)
    In:  Other Sources
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    Publication Date: 2018-12-01
    Description: A review of recent calculations obtained with Bird's direct simulation Monte Carlo (DSMC) method are presented for the transitional flowfield encountered at reentry conditions. Consequently, the emphasis is to simulate the real-gas effects resulting from a highly energetic nonequilibrium flow. The DSMC calculations for both wide-angle and slender bodies are compared with experimental and continuum calculations. The wide angle body calculations simulate the windward nose of the Shuttle Orbiter and projected aeroassisted orbital transfer vehicles. For the slender, blunted configurations, both two-dimensional and axisymmetric results are presented. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant.
    Keywords: AERODYNAMICS
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  • 20
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    DSMC calculations for 70-deg blunted cone at 3.2 km/s in nitrogen (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Numerical results obtained with the direct simulation Monte Carlo (DSMC) method are presented for Mach 15.6 nitrogen flow about a 70-deg spherically blunted cone at zero incidence. This flow condition is one of several generated in the Large Energy National Shock (LENS) tunnel during tests of a 15.24 cm diameter model with an afterbody sting. The freestream Knudsen number, based on model diameter, is 0.0023. The focus of the DSMC calculations is to characterize the near wake flow under conditions where rarefaction effects may influence afterbody aerothermal loads. This report provides information concerning computational details along with flowfield and surface quantities. Calculations show that the flow enveloping the test model is in thermal nonequilibrium and a sizable vortex develops in the near wake. Along the model baseplane the heating rates are about 0.6 percent of the forebody stagnation value while the maximum heating along the sting is about 4.2 percent of the forebody stagnation value. Comparison of a Navier-Stokes solution with the present calculations show good agreement for surface heating, pressure, and skin friction results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-109181 , NAS 1.15:109181
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