Nonlinear Internal Flow Analysis
Final rept. 22 Sep 95-10 Feb 97
CSA ENGINEERING INC PALO ALTO CA
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Space re-entry vehicles like ICBMs, manned space crafts, and space shuttles are subjected to excessive heat fluxes at the time of space re-entry. One method of preventing high internal temperatures is to let the outer surface ablate. While this solves the problem of overheating and protects the internal structure of these vehicles, it also changes the shape of these vehicles and makes them unsuitable from an aerodynamic viewpoint. This disadvantage can be overcome by using internal ablators protected by a fixed shape outer radiating structure. During periods of excessive heating internal ablation occurs, and the gaseous products transpire through the outer porous radiating structure. In this report, a simple one dimensional analysis of the thermal ablation problem is presented. The model consists of a fixed shape outer structure whose temperature is limited to T. An ablator is placed behind this outer structure. The ablator is assumed to act like a heat sink both in terms of mass supply and thermal energy supply so that it can be assumed to be at a constant temperature Tb. When the surface temperature of the ablator Ts rises due to heat radiation and reaches a value of Ta, it ablates and gaseous products transpire through the fixed outer surface thereby reducing the heat transfer to the outer surface. The heat transfer mechanism between the outer structure and the ablation surface is by radiation across the gap. Of the heating rate qot incident on the outer structure, a part qr,ot is radiated outward while the rest qr,it is radiated inward to the ablation surface. When ablation occurs, the surface temperature of the ablator increases to a fixed value of Ta.