William D. Henline

Comparison of coupled radiative flow solutions with Project Fire II flight data

A nonequilibrium, axisymmetric, Navier-Stokes flow solver with coupled radiation has been developed for use in the design or thermal protection systems for vehicles where radiation effects are important. The present method has been compared with an existing now and radiation solver and with the Project Fire 2 experimental data. Good agreement has been obtained over the entire Fire 2 trajectory with the experimentally determined values of the stagnation radiation intensity in the 0.2-6.2 eV range and with the total stagnation heating. The effects of a number of flow models are examined to determine which combination of physical models produces the best agreement with the experimental data. These models include radiation coupling, multitemperature thermal models, and finite rate chemistry. Finally, the computational efficiency of the present model is evaluated. The radiation properties model developed for this study is shown to offer significant computational savings compared to existing codes.

Mars Pathfinder Trajectory Based Heating and Ablation Calculations

The Mars Pathfinder probe will enter the Martian atmosphere at a relative velocity of 7.65 km/s. The 2.65-m-diam vehicle has a blunted, 70-deg-half-angle, conical forebody aerobrake. Axisymmetric time-dependent calculations have been made using Gauss-Seidel implicit aerothermodynamic Navier-Stokes code with thermochemical surface conditions and a program to calculate the charring-material thermal response and ablation for heating analysis and heat-shield material sizing. The two codes are loosely coupled. The flovvfield and convective heat-transfer coefficients are computed using the flowfield code with species balance conditions for an ablating surface. The timedependent in-depth conduction with surface blowing is simulated using the material response code with complete surface energy-balance conditions. This is the first study demonstrating that the computational fluid-dynamics code interfacing with the material response code can be directly applied to the design of thermal protection systems of spacecraft. The heat-shield material is SLA-561V. The solutions, including the flowfield, surface heat fluxes and temperature distributions, pyrolysis-gas blowing rates, in-depth temperature history, and minimum heat-shield thicknesses over the aeroshell forebody, are presented and discussed in detail. The predicted heat-shield mass is about 20 kg.

Comparison of Coupled Radiative Navier-Stokes Flow Solutions with the Project Fire II Flight Data

A nonequilibrium, axisymmetric, Navier-Stokes flow solver with coupled radiation has been developed to use in the design of thermal protection systems for vehicles where radiation effects are important. The present method has been compared with an existing flow and radiation solver and with the Project Fire II experimental data. Very good agreement has been obtained over the entire Fire II trajectory with the experimentally determined values of the stagnation radiation intensity in the .2 to 6.2 eV range and with the total stagnation heating. The agreement was significantly better than previous numerical predictions. The effects of a number of flow models are examined to determine which combination of physical models produces the best agreement with the experimental data. These models include radiation coupling, multi-temperature thermal models, finite-rate chemistry, and a quasi-steady-state or Boltzmann assumption for the calculation of the excited electronic states. Finally, the computational efficiency of the present model is evaluated. The radiation properties model developed for this study is shown to offer significant computational savings compared to existing codes.

Navier-Stokes Heating Calculations for Benchmark Thermal Protection System Sizing

A study was carried out to identify, select, and benchmark simulation techniques needed for thermal protection material selection and sizing for reusable launch vehicles. Fully viscous, chemically reacting, Navier-Stokes solutions for the flow around a sphere are generated and compared using three different flow solvers. The effects of grid resolution, algorithm, transport modeling, and surface boundary conditions on the magnitude and convergence of the predicted heat transfer rate are examined. A third-order Van Leer inviscid upwind flux formulation was found to be a good method for surface heat transfer predictions. A number of three-dimensional, chemically reacting, Navier-Stokes flow solutions are generated for the nose of a single-stage-to-orbit rocket at angle of attack. A methodology for thermal protection system material selection is demonstrated. The strong influence of thermal protection system material selection on predicted heat transfer rates and surface temperatures is demonstrated. Further, it is shown that the changes in surface emissivity and catalycity at the interfaces between different thermal protection system concepts can produce large jumps in the predicted surface temperature. These gradients must be accounted for in the thermal protection system and vehicle design process.

Navier-Stokes solutions with surface catalysis for Martian atmospheric entry

In this study numerical solutions have been obtained for two-dimensional axisymmetric hypersonic nonequilibrium CO2 flow over a high angle blunt cone with appropriate surface boundary conditions to account for energy and mass conservation at the body surface. The flowfield is described by the Navier-Stokes equations and multicomponent conservation laws which account for both translational and internal vibrational nonequilibrium effects. Complete forebody solutions have been obtained for the peak heating point of the Mars entry trajectory specified in the proposed NASA MESUR (Mars Environmental Survey) project. In these solutions, radiative equilibrium wall temperature and surface heating distributions are determined over the MESUR aeroshell forebody for entry velocity equal to 7 km/sec with varying degrees of surface catalysis. The effects of gas kinetics, surface catalysis, transport properties, and vibrational relaxation times on the surface heating are examined. The results identify some important issues in the prediction of surface heating for flows in thermochemical nonequilibrium and show that the Navier-Stokes code used herein is effective for thermal protection system design and materials selection.