Thermo-chemical nonequilibrium effects on the aerothermodynamics of hypersonic vehicles

A three-dimensional computational fluid dynamics algorithm is developed to study the effect of thermal and chemical nonequilibrium on blunt and slender body aerothermodynamics. Both perfect gas and reacting gas air models are used to compute the flow over several hypersonic vehicles. The reacting air mixture is characterized by a translational-rotational temperature and a vibrational-electron-electronic temperature and includes eight chemical species. The Navier-Stokes computations are compared to wind tunnel and flight data where available to examine the effects of chemical reaction, vibrational excitation, and ionization on lift-to-drag ratio and trim angle of attack. A modified Diagonal Implicit time advancement scheme is developed to handle flows in thermo-chemical nonequilibrium and is shown to have improved convergence behavior as compared to a previous method.; Results from the numerical algorithm are compared to computations from other investigators for Project Fire II. Flow and surface properties are found to be in good agreement for axisymmetric non-ionized and ionized flows.; Perfect gas and five species air reacting gas models are used to compute the flow over the Apollo Command Module and are compared to wind tunnel and flight aerodynamic data from the unmanned Apollo AS-202 mission. A lower trim angle of attack and lift-to-drag ratio results from including effects of dissociation and vibrational nonequilibrium when compared to predictions by non-reacting gas wind tunnel simulations. Both perfect gas and reacting gas calculations compare well with the wind tunnel and flight data, respectively, and the results are consistent with the observed aerodynamic trends.; Results over a generic transatmospheric vehicle show significant differences in center of gravity location between typical flight and tunnel configurations at the same Mach number, Reynolds number, and trim angle of attack. For the same center of gravity location, the wind tunnel model trims at lower angle of attack than the full scale flight case.; Non-ionized and ionized results for a proposed lunar transfer vehicle compare well to computational results obtained from a previously validated reacting gas algorithm. Under the conditions investigated, effects of weak ionization on the heat transfer and aerodynamic coefficients were minimal.; The results obtained demonstrate that the computation of nonequilibrium, reacting gas flows in three dimensions can be accomplished in an efficient manner. Real gas effects are shown to significantly influence the aerothermodynamic behavior of two classes of hypersonic vehicles. This work gives evidence that proper modeling of the physical processes is essential for hypersonic vehicle design.