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Gupta, Roop N.

Publications and source records attributed to Gupta, Roop N..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Aerothermodynamic Analysis of Stardust Sample Return Capsule with Coupled Radiation and Ablation

An aerothermodynamic analysis of the forebody aeroshell of the Stardust Sample Return Capsule is carried out by using the axisymmetric viscous shock-layer equations with and without fully coupled radiation and ablation. Formulation of the viscous shock-layer equations with shoulder radius as the length scale and implementation of the Vigneron pressure condition allow resolution of the flowfield over the shoulder. With a predominantly supersonic outflow over the shoulder, a globally iterated solution or viscous shock-layer equations can be obtained. The stagnation-point results are obtained along a specified trajectory, whereas detailed calculations along the body are provided at the peak-heating point. The equilibrium calculations with ablation injection are the focus of the present study because of the lack of a general chemical nonequilibrium analysis that accounts for both surface and flowfield effect. The equilibrium calculations also provide a simple way to conserve surface (and flowfield) elemental composition for the current small ablation injection rates, where the surface elemental composition is a mixture of freestream and ablator elements. Therefore, the coupled laminar and turbulent flow solutions with radiation and ablation are obtained by using the equilibrium flow chemistry, whereas a nonequilibrium chemistry model is used for solutions without ablation and turbulence. Various computed results are compared with those obtained by the other researchers.

Gupta, Roop N.↗
NASA NTRS1996

DSMC simulations of OREX entry conditions

Results of direct simulation Monte Carlo (DSMC) solutions are presented for the Japanese Orbital Reentry Experiment (OREX) vehicle, a 50 deg half-angle spherically blunted cone with a nose radius of 1.35 m and a base diameter of 3.4 m. The flow conditions simulated are those for entry into the Earth's atmosphere at a nominal velocity of about 7.4 km/s and zero incidence. Calculations are made for the higher altitude portion of entry, encompassing the transitional flow regime (altitudes of 200 to 80 km). Comparisons with flight measured values are made for axial acceleration, surface pressure, and stagnation point heating.

Moss, James N.↗
NASA NTRS1996

Assessment of thermochemical nonequilibrium and slip effects for Orbital Reentry Experiment (OREX)

Results are provided from a viscous shock layer (VSL) analysis of the reentry flowfield around the forebody of the Japanese Orbital Reentry Experiment (OREX) vehicle. This vehicle is a 50 deg. spherically blunted cone with a nose radius of 1.35 m and a base diameter of 3.4 m. Calculations are done for the OREX trajectory from 105 to 48.4 km altitude range. A 7-species chemical model is found adequate for the flowfield analysis. However, for altitudes greater than 84 km, the low density effects (such as thermal nonequilibrium and slip) are to be implemented for good agreement between the predictions and flight inferred heat-transfer rate data. Further, at altitudes lower than 84 km, a finite surface recombination probability is to be employed in place of a non-catalytic surface for better comparison between the calculations and data. VSL results are also compared with the direct simulation Monte Carlo (DSMC) predictions at high altitudes (greater than 80 km) and the electron number density data for three altitudes in the OREX trajectory. Overall, there is a good comparison between the flight data and calculated results. With the ongoing refinements in data extraction procedures, the OREX data should prove valuable for validating theoretical models employed in flowfield codes for calculation of reacting-gas flowfields.

Gupta, Roop N.↗
NASA NTRS1994

Viscous Shock-Layer Analysis of Two-Dimensional and Axisymmetric Flows

Results are obtained for cylindrical leading edges of proposed transatmospheric vehicles by employing a two-dimensional viscous shock-layer code for nonequilibrium gas flows. The accuracy and efficiency of the planar code is verified through detailed comparisons with other predictions. This study includes results for 6-deg half-angle bodies with nose radii ranging from 0.01 to 2.0 ft for both cylindrically blunted wedges and spherically blunted cones (included for comparison). Some results are presented as a ratio of the noncatalytic to the corresponding fully catalytic heating value to illustrate the maximum potential for a heating reduction in dissociated nonequilibrium flows. Generally, this ratio and the individual heating rates are smaller for cylindrically blunted wedges with small nose radii as compared to the spherically blunted cones (for the same nose radius). Therefore, a larger potential exists for heating reduction in cylindrically blunted as compared with the spherically blunted surfaces. However, the results presented at higher altitudes (where the slip effects become important) show that the spherically, blunted nose gives lower stagnation-point heating due to stronger merged shock-layer effects as compared with a cylindrically blunted nose.

Gupta, Roop N.↗
NASA NTRS1994

Computing Thermodynamic And Transport Properties Of Air

EQAIRS computer program is set of FORTRAN 77 routines for computing thermodynamic and transport properties of equilibrium air for temperatures from 100 to 30,000 K. Computes properties from 11-species, curve-fit mathematical model. Successfully implemented on DEC VAX-series computer running VMS, Sun4-series computer running SunOS, and IBM PC-compatible computer running MS-DOS.

Thompson, Richard A.↗
NASA NTRS1993

Higher-order viscous shock-layer solutions for high altitude flows

A higher-order viscous shock-layer (HVSL) method has been developed and is used to obtain physically consistent results under varying degrees of low-density conditions for perfect-gas and nonequilibrium flows past long slender bodies. This method is implemented with higher-order body and shock slip conditions. Detailed comparisons with the direct simulation Monte Carlo (DSMC) method and Navier-Stokes (NS) calculations establish HVSL as a computationally efficient code for the low-density calculations. Further, it is shown that the deficiencies in the standard viscous shock-layer (VSL) method when predicting low-density flows lie in the governing equations and not with the slip boundary conditions as considered by earlier researchers.

Gupta, Roop N.↗
NASA NTRS1993

A viscous shock-layer analysis of 2-D and axisymmetric flows

Results are obtained for cylindrical leading edges of proposed transatmospheric vehicles by employing a 2D viscous shock-layer code for nonequilibrium and perfect gas flows. The accuracy and efficiency of the planar code is verified through detailed comparisons with other predictions. It is found to be as accurate and robust as its axisymmetric counterpart. This study includes results for nose radii ranging from 0.01 to 2.0 ft and half-angles of 5 and 6 deg for both cylindrically-blunted wedges and spherically blunted cones (included for comparison). Some results are presented as a ratio of the noncatalytic to the corresponding fully catalytic heating value to illustrate the maximum potential for a heating reduction in dissociated nonequilibrium flows. This ratio and the individual heating rates are smaller for cylindrically-blunted wedges with small nose radii, relative to the spherically-blunted cones (at the same radius). Therefore, a larger potential exists for heating reduction in cylindrically-blunted as compared with the spherically-blunted surfaces for finite-rate chemistry.

Gupta, Roop N.↗
NASA NTRS1993

Stagnation flowfield analysis for an aeroassisted vehicle

Hypersonic reactive flowfield results are presented for the flow about an axisymmetric representation of a three-dimensional aeroassisted vehicle using the viscous shock-layer (VSL) and Navier-Stokes (NS) equations for low- and high-altitude entry conditions, respectively. Solutions are limited to the stagnation region. The NS results have been obtained by employing the surface recombination boundary condition for an 11-species air model, whereas the VSL calculations are carried out by using a 5-species model. Three widely used surface recombination rate models are implemented with these two flowfield calculation procedures. The low-density (or high altitude) NS solutions are obtained with surface slip equations and compare quite well with the direct simulation Monte Carlo predictions. For higher densities (or lower altitudes), the no-slip VSL solutions are considered adequate. Results from this study highlight the effect of surface catalyticity on surface heating and electron number density.

Gupta, Roop N.↗
NASA NTRS1992

Viscous equilibrium computations using program LAURA

Modifications have been made to the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) that enable it to compute viscous airflows under the assumption of thermal and chemical equilibrium. Equilibrium thermodynamic and transport property information are input to the code via curve fits. The periodic updating of this information enables the equilibrium algorithm to perform at a computational rate that is only a small percentage larger than the rate associated with the perfect-gas algorithm. Presented in this article are the results of the initial validation of the modified code. Solutions for surface pressure and heating are presented for the flow over slender and blunt cones at realistic reentry conditions. LAURA solutions are compared with those produced by a viscous shock-layer method, and, for one case considered, with heat transfer data from a flight experiment. For both pressure and heating, the agreement is good. In general, differences in pressure of a few percent were noted, while differences in heating rates were in the 5-10 percent range.

Greene, Francis A.↗
NASA NTRS1992

Stagnation-point heat-transfer rate predictions at aeroassist flight conditions

The results are presented for the stagnation-point heat-transfer rates used in the design process of the Aeroassist Flight Experiment (AFE) vehicle over its entire aeropass trajectory. The prediction methods used in this investigation demonstrate the application of computational fluid dynamics (CFD) techniques to a wide range of flight conditions and their usefulness in a design process. The heating rates were computed by a viscous-shock-layer (VSL) code at the lower altitudes and by a Navier-Stokes (N-S) code for the higher altitude cases. For both methods, finite-rate chemically reacting gas was considered, and a temperature-dependent wall-catalysis model was used. The wall temperature for each case was assumed to be radiative equilibrium temperature, based on total heating. The radiative heating was estimated by using a correlation equation. Wall slip was included in the N-S calculation method, and this method implicitly accounts for shock slip. The N-S/VSL combination of projection methods was established by comparison with the published benchmark flow-field code LAURA results at lower altitudes, and the direct simulation Monte Carlo results at higher altitude cases. To obtain the design heating rate over the entire forward face of the vehicle, a boundary-layer method (BLIMP code) that employs reacting chemistry and surface catalysis was used. The ratio of the VSL or N-S method prediction to that obtained from the boundary-layer method code at the stagnation point is used to define an adjustment factor, which accounts for the errors involved in using the boundary-layer method.

Gupta, Roop N.↗
NASA NTRS1992

Enhancements to viscous-shock-layer technique

A solution procedure is presented which considerably improves the computational efficiency of the viscous-shock-layer technique, especially for long slender bodies. The 'predictor-corrector' procedure suggested for obtaining the shock shape beyond the nose region requires only a single global pass. The accuracy of the present method is demonstrated by comparison with globally iterated results over the entire body and with ground- and flight-test data. A good comparison of the results computed with the two methods is shown for different flowfield chemistry models and axisymmetric body shapes. The new procedure results in computer run times 1/3 to 1/2 of the times required for the full-body global iteration procedure. Further, the algebraic expressions used to specify the initial shock shape eliminate the need for a shock shape generated by external means and permit immediate introduction of the full viscous-shock-layer equations. Finally, the present method of solution for the VSL equations provides to the aerothermal designer a very efficient and accurate tool for detailed flowfield as well as future technology studies.

Gupta, Roop N.↗
NASA NTRS1992

Viscous-shock-layer analysis of hypersonic flows over long slender vehicles

An efficient and accurate method for solving the viscous shock layer equations for hypersonic flows over long slender bodies is presented. The two first order equations, continuity and normal momentum, are solved simultaneously as a coupled set. The flow conditions included are from high Reynolds numbers at low altitudes to low Reynolds numbers at high altitudes. For high Reynolds number flows, both chemical nonequilibrium and perfect gas cases are analyzed with surface catalytic effects and different turbulence models, respectively. At low Reynolds number flow conditions, corrected slip models are implemented with perfect gas case. Detailed comparisons are included with other predictions and experimental data.

Lee, Kam-Pui↗
NASA NTRS1992

Eleven-Species Thermochemical Model Of Air

SPECIES program computes thermodynamic and transport properties and equilibrium constants. Uses least-squares polynomial curve fits of most accurate data available to provide requested values more quickly than table-lookup methods. Subroutines computing transport coefficients and collision cross sections include additional code to correct for any electron pressure when working with ionic species. Species represented: diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Written in FORTRAN 77.

Thompson, Richard A.↗
NASA NTRS1991

Calculations and curve fits of thermodynamic and transport properties for equilibrium air to 30000 K

A self-consistent set of equilibrium air values were computed for enthalpy, total specific heat at constant pressure, compressibility factor, viscosity, total thermal conductivity, and total Prandtl number from 500 to 30,000 K over a range of 10(exp -4) atm to 10(exp 2) atm. The mixture values are calculated from the transport and thermodynamic properties of the individual species provided in a recent study by the authors. The concentrations of the individual species, required in the mixture relations, are obtained from a free energy minimization calculation procedure. Present calculations are based on an 11-species air model. For pressures less than 10(exp -2) atm and temperatures of about 15,000 K and greater, the concentrations of N(++) and O(++) become important, and consequently, they are included in the calculations determining the various properties. The computed properties are curve fitted as a function of temperature at a constant value of pressure. These curve fits reproduce the computed values within 5 percent for the entire temperature range considered here at specific pressures and provide an efficient means for computing the flowfield properties of equilibrium air, provided the elemental composition remains constant at 0.24 for oxygen and 0.76 for nitrogen by mass.

Gupta, Roop N.↗
NASA NTRS1991

Computer codes for the evaluation of thermodynamic and transport properties for equilibrium air to 30000 K

The computer codes developed here provide self-consistent thermodynamic and transport properties for equilibrium air for temperatures from 500 to 30000 K over a temperature range of 10 (exp -4) to 10 (exp -2) atm. These properties are computed through the use of temperature dependent curve fits for discrete values of pressure. Interpolation is employed for intermediate values of pressure. The curve fits are based on mixture values calculated from an 11-species air model. Individual species properties used in the mixture relations are obtained from a recent study by the present authors. A review and discussion of the sources and accuracy of the curve fitted data used herein are given in NASA RP 1260.

Thompson, Richard A.↗
NASA NTRS1991

Flight stagnation-point heating calculations on Aeroassist Flight Experiment vehicle

NASA's Aeroassist Flight Experiment (AFE) vehicle will be deployed from the Space Shuttle Orbiter in 1994 to make a data-gethering aeropass through the upper atmosphere before returning to orbit for Shuttle pickup. An axisymmetric, chemically-reacting viscous shock-layer code is presently used to calculate AFE heating rates which automatically accounts for the viscous-inviscid interaction and entropy layer-swallowing effects which are ignored by the conventional boundary-layer methods. Results are presented for the stagnation-point heating of the current AFE baseline trajectory.

Hamilton, H. H., II↗