CALCULATION OF REAL-GAS EFFECTS ON BLUNT-BODY TRIM ANGLES

The effect of vibrational excitation and dissociation at high temperatures on the trim angle of attack of a blunt lifting body is calculated for a nonequilibrium flow regime in air using a computational fluid dynamics technique. Air is considered to consist of five neutral species, O, N, NO, O2, and N2, and both one- and two-temperature thermochemical nonequilibrium models are used in determining the thermodynamic state. A computer code, named CENS2H (Compressible Euler-Navier-Stokes Two-dimensional Hypersonic), is developed by incorporating this model into an existing perfect-gas code named CENS2D, which uses a lower-upper factorization based on the symmetric Gauss-Seidel sweeping technique. The code is applied to compute the forebody flow of a two-dimensional blunt body of the shape of the Apollo Command Module at a finite angle of attack. The results show that the trim angle of attack is smaller for a reacting gas than for a perfect gas. The calculated shift in the trim angle due to the real-gas effect is of the same order as that seen during the Apollo flights. The one-temperature nonequilibrium model yields the same trim angles as the two-temperature model, but the constant-gamma (= C(p)/C(v)) solution that reproduces the shock standoff distance fails to reproduce the trim angle.