Viscous Shock Layer Method Research Articles

Stagnation-point heating of Fire II with a non-Boltzmann radiation model

The present work analyzes the stagnation-point radiative heating in the Fire II flight experiment by devising a collisional-radiative model with non-local absorption. In the stagnation-line flow-field calculations, a viscous shock layer method with a thermochemical nonequilibrium model is utilized. In the radiation calculations, a line-by-line method with the non-Boltzmann electronic populations is employed by adopting the quasi-steady state approach of the electronic master equation calculations. In constructing the electronic master equation, the best set of the electron and heavy-particle impact excitation rates is proposed to achieve better agreement with the measured radiative heating flight data. In the flow-radiation coupling procedure, the effect of the non-local absorption is modeled by devising an iterative process between the quasi-steady state electronic master equation and the radiative transfer equation calculations. Escape factors of the strongest atomic lines and the diatomic nitrogen vacuum ultraviolet systems with the non-local absorption effect are also proposed to more efficiently consider the non-local nature of the radiative transition. When compared with the experimental data from the Fire II trajectories, it is found that the present collisional-radiative model with the non-local absorption improves the ability to predict non-Boltzmann radiative heating.

Viscous Shock Layer Method to Predict Communication Blackout during Re-entry Phase

Communication blackout generally occurs during the re-entry at high velocities through the atmosphere. Air ahead of the re-entry vehicle dissociates and then ionises, leading to the production of electrons. These electrons may reflect or attenuate the communication signals. Electron densities with plasma frequency exceeding the communication frequency lead to blackout. Electron density is a function of the body shape, velocity and altitude. The viscous shock layer method is used to predict the electron density, and thereby the plasma frequency for various configurations. This method is successfully implemented for analytic and non-analytic geometry configurations available in the literature. The electron densities computed for the RAM-C configuration agree well with the flight results. The onset of blackout during the re-entry phase is also predicted reasonably well by this method. The method performs well at high altitudes, where nonequilibrium conditions prevail. Defence Science Journal, 2011, 61(4), pp.364-369 , DOI:http://dx.doi.org/10.14429/dsj.61.1089

Stagnation-Region Heating Environment of the Galileo Probe

The heating and ablating environment of the shock layer in the stagnation region of the Galileo probe is analyzed. Viscous shock-layer method is used assuming thermochemical equilibrium. Improvement is made to the existing methodology in calculating the equilibrium composition, radiation absorption in the vacuum ultraviolet wavelength range, and the effect of spallation. The calculated surface recession at the stagnation point agrees fairly closely with the flight data.

Calculation of Stagnation-Point Heating Rates Associated with Stardust Vehicle

Stagnation-point heating rate is calculated for the Stardust entry vehicle and for its heat-shieldmodels tested in an arcjetwind tunnel. The calculations aremade for the convective component for both the laminar and turbulent cases, the radiative component produced by the gas flow, and the radiative component produced by solid particles. A onedimensional viscous shock layer method is used with an up-to-date thermochemical, gas–surface interaction, radiation, turbulence, and particulate models. For the flight cases, radiation absorption in the boundary layer is found to increase the convective heating rate by a factor of up to two. The calculated sums of all heating rates for the flight cases are nearly the same as those obtained by Olynick et al., and are substantially larger than those by Gupta. The calculated sums of all heating rates for the arcjet test cases are smaller than those calculated by the formula of Fay and Riddell, and are nearly the same as those experimentally determined using copper calorimeters.

Stagnation-Point Heat Transfer Rates for Pioneer-Venus Probes

Summary The convective and radiative heat transfer rates are calculated for the stagnation region of the Pioneer- Venus Probe vehicles during their entry flights into the planet Venus. The nonequilibrium thermochemical state of the flow is calculated using a viscous shock layer method accounting for oxidation of heatshield surface by atomic oxygen and for pyrolysis-gas injection. Radiative transport along the stagnation streamline is calculated using a lineby-line technique and tangent-slab approximation. For both radiative and convective heating rates, the present results are substantially smaller than the earlier values obtained assuming equilibrium.

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.

Thermochemical nonequilibrium issues for earth re-entry of Mars mission vehicles

The thermochemical environment about an axisymmetric 60-deg sphere-cone with a circular aft skirt is computed using the Langley Aerothermodynamic Upwind Relaxation Algorithm. Earth entry at 12 km/sec is examined at 70-km and 80-km altitude for two vehicle base radii of 2 m and 6 m. These four test cases bracket some proposed scenarios for earth reentry of a manned Mars mission aerobrake at this velocity. Thermochemical nonequilibrium results are examined for each case and compared with thermal equilibrium results produced by artificially accelerating vibrational relaxation rates and with equilibrium results produced by a viscous shock layer method.

Approximate viscous shock-layer method for hypersonic flow over blunt-nosed bodies

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Hypersonic-finite rate chemically reacting viscous flows over an ablating carbon surface

Hypersonic finite-rate chemically reacting viscous flows over an ablating carbon surface have been analyzed using the viscous shock-layer method to study the effects of ablating carbon on the surface-measurable quantities and on the electron density, temperature, and species profiles across the shock layer. The results for nonequilibrium air injection and the ablating carbon surface mass transfer were compared. Of all the test cases considered, the ablating carbon case shows an approximately 10°7o higher stagnation heat-transfer rate than the equivalent nonequilibrium air injection case. The effects of fully catalytic, noncatalytic, and equilibrium catalytic wall boundary conditions were also compared to analyze the effects of catalytic wall boundary conditions on the heat-transfer rate. At low wall temperatures, such as 1000 K, the noncatalytic wall condition showed the lowest heat-transfer rate. However, at high wall temperatures (such as 3333 K) due to the positive wall diffusion heat transfer, the equilibrium catalytic wall condition showed the lowest heat-transfer rate at an altitude of 84 km and a freestream velocity of 7.6 km/s. A method for analyzing nonequilibrium finite-rate chemically reacting flows over multiconic geometries with ablating carbon surface has been developed.

Three-dimensional nonequilibrium viscous flow over the Shuttle Orbiter with catalytic surface effects

Computational results are presented for the three-dimensional nonequilibrium flowfield over the entire windward surface of a modified Shuttle-like geometry at high angles of attack (up to 50 deg). The viscous shocklayer method used takes into account the finite rate chemical reactions of multicomponen t ionizing air, and the governing equations are written in a general nonorthogonal computational grid system. Boundary conditions considered include noncatalytic wall, finite catalytic wall, fully catalytic wall, and nonequilibrium slip conditions at the wall and/or shock. The nonequilibrium solutions are compared with equilibrium air solutions, perfect gas solutions, and Shuttle flight heat-transfer and pressure data, and the comparisons show good agreement and correlations between the nonequilibrium solutions and the flight data. Three-dimensional effects are clearly shown in the flight derived data for the first time based upon the results of this study.

Three-dimensional nonequilibrium viscous shock-layer flow over the Space Shuttle Orbiter

A numerical method has been developed to predict the three-dimensional nonequilibrium flowfield past the Space Shuttle Orbiter at high angle of attack. An existing viscous shock-layer method has been extended to include finite-rate chemical reactions of multicomponen t ionizing air. A general nonorthogonal computational grid system was introduced to treat the nonaxisymmetric geometry. At Shuttle re-entry flight conditions, nonequilibrium real gas effects on the surface-measurable quantities are significant. The present method can predict the nonequilibrium flowfield over the entire windward surface of the Shuttle Orbiter at high angle of attack (up to 50 deg). The computational results obtained show good agreement compared to the STS-2 flight data and other numerical solutions.