Nonequilibrium Viscous-Layer Computations of Space Shuttle TPS Requirements

Abstract

The thermal protection system requirements on the windward pitchplane of a typical shuttle orbiter are evaluated using a recently developed computational procedure. This procedure treats chemically nonequilibrium inviscid and viscous flows for surfaces of arbitrary catalycity. Surface catalycities for typical shuttle materials were evaluated from arc plasma generator data. Computations for the shuttle orbiter demonstrated the significance of entropy swallowing on heat transfer and show that for representative catalycity values, nonequilibrium effects are small though not insignificant. It is shown that the reduced heat transfer rates, caused by surface effects, observed in arc plasma facilities, should be reviewed carefully since these reduced rates will not be as significant for the larger orbiter dimensions. NomenclatureH T = total enthalpy k w (O) = surface catalycity for O recombination k w (N) = surface catalycity for N recombination M e = boundary-layer edge Mach number MOO = freestream or flight Mach number P = pressure Pt 2 = total pressure behind a normal shock wave q = heat flux <? cat = heat flux to catalytic surface Re e = Reynolds number based on momentum thickness s = surface or stream wise coordinate / = time C/oo = freestream or vehicle velocity a. = vehicle angle of attack

Nonequilibrium excitation of internal molecular degrees of freedom in the shock layer during hypersonic flight

“…Curves 3 -3" and 4 were obtained at rate constants of the heterogeneous recombination of oxygen and nitrogen atoms K~ m/s and -'N K~ =3.1 m/s, respectively. These constants are characteristic for the surface of RSV (Tong et al 1975). The surface temperature was determined from the equation of balance of the convective heat flux to the surface and the radiation heat flux from it, the emissivity of the surface being equal to 0.8.…”

“…As mentioned above, the heterogeneous processes (M=surface) are more effective for the reactions of recombination but the heterogeneous recombination N+O+Surface , NO+Surface is not usually taken into account (Zoby 1983;Tong et al 1975;Kolesnikov and Yakushin 1989); b) the exchange reactions…”

“…The characteristic radius of the nose of space shuttle at the stagnation point is Rb=0.815 m (Tong et al 1975). The typical gasdynamic flow time at the stagnation point may be evaluated as ra = Rb/U~, U~ is velocity of the incident gas flow.…”