In 2024, Metacomp presented at the Thermal & Fluids Analysis Workshop at NASA Glenn Research Center on hypersonic aerothermodynamics modeling of two reentry flight experiments using CFD++: RAM-C II vehicle and OREX capsule.
The Radio Attenuation Measurement (RAM) program was conducted in the 1960s to study communications blackout in hypersonic reentry flows. Figure 1 shows the RAM-C II model. CFD++ simulations were performed using the thermal non-equilibrium model. Due to the uncertainty of the catalytic behavior at the wall, various boundary conditions were used for each flight condition: non-catalytic, fully catalytic and partially catalytic. Mixture transport properties were calculated using Gupta’s mixing rules with species viscosities and thermal conductivities calculated using collision cross-section data. An 11-species finite rate chemistry model for air was used for all cases and the rates were taken from Park 1993. Three flight conditions were simulated: 61, 71 and 81 km. Figure 2 shows comparisons with reflectometer dataindicating that the catalytic behavior of the surface changes as the vehicle descends through the atmosphere, transitioning from a fully catalytic to a partially catalytic wall.
The OREX (Orbital Reentry Experiments) capsule shown in Figure 3, was a flight experiment planned as a part of the Japanese HOPE (H-11 Orbiting Plane) project that was launched in February 1994 from the Tanegashima Space Center in Japan and successfully acquired flight data of the aerothermal environment of the probe. CFD++ simulations were performed over 12 trajectory points using the thermal non-equilibrium model. A 7-species air chemistry model with reaction rates from Park 1993 was used. Mixture transport properties were calculated using Gupta’s mixing rules with species viscosities and thermal conductivities calculated using collision cross-section data. The species diffusion was modeled using the high-fidelity binary diffusion model with the Ramshaw effective diffusion model. An isothermal condition was assumed at the wall with a uniform wall temperature inferred from flight data.
Three different catalytic models were considered to describe the species behavior at the wall: non-catalytic, partially catalytic and fully catalytic. The flight data indicates that the heat flux increases with decreasing altitude, peaks around 65km, and then gradually decreases at lower altitudes. Stagnation point heat flux results are shown in Figure 4. As expected, the fully catalytic model predicts the highest heat flux, as such walls promote recombination reactions, releasing additional heat at the surface. On the other hand, the non-catalytic model predicts the lowest heat flux, as surface recombination reactions are absent, resulting in reduced heat transfer to the surface. The partially catalytic model agrees well with the flight data, indicating a moderate recombination rate.
