Effects of forced and free convections on structural temperatures of Space Shuttle Orbiter during reentry flight

Structural performance and resizing (SPAR) finite-element thermal analysis computer program was used in the heat transfer analysis of the Space Shuttle Orbiter wing subjected to reentry aerodynamic heating. With sufficient external forced convective cooling near the end of the heating cycle, the calculated surface temperatures of the thermal protection system (TPS) agree favorably with the flight data for the entire flight profile. However, the effects of this external forced convective cooling on the structural temperatures were found to be negligible. Both free convection and forced convection elements were introduced to model the internal convection effect of the cool air entering the Shuttle interior. The introduction of the internal free convection effect decreased the calculated wing lower skin temperatures by 20 F at most, 1200 sec after touchdown. If the internal convection is treated as forced convection, the calculated wing lower skin temperatures after touchdown can be reduced to match the flight-measured data very closely. By reducing the TPS thicknesses to certain effective thickness to account for the TPs gap heating, the calculated wing lower skin temperatures prior to touchdown can be raised to agree with the flight data perfectly.