Thermo-chemical nonequilibrium effects on the aerothermodynamics of aerobraking vehicles

A three-dimensional computational fluid dynamics algorithm is developed to study the effect of chemical and thermal nonequilibrium on blunt body aerodynamics. Both perfect gas and five species air reacting gas models are used to compute the flow over the Apollo command module. The reacting gas air mixture is assumed to be governed by a translational-rotational temperature and a vibrational temperature. The Navier-Stokes computations are compared to wind-tunnel and flight-aerodynamic data from the Apollo missions. The effects of chemical reaction and vibrational excitation on lift-to-drag ratio and trim angle are investigated. It is shown that including real gas effects results in a lower trim angle and L/D than predicted by nonreacting gas wind-tunnel simulations. The reacting gas numerical results are consistent with flight data from the unmanned Apollo AS-202 mission, whereas the perfect gas computations agree with the extrapolated preflight wind-tunnel results.