Effects of Gap Height and Geometry on Supersonic Aerothermal Gap Heating

The gap created between a missile’s fuselage and its control fin is a crucial point on the vehicle. To ensure safe flight, and to prevent damage to the gap surfaces, the thermal management inside the gap must be investigated. Using UTK’s variable Mach low-enthalpy supersonic wind tunnel, three torque-tube base geometries (right-angle corner, rounded corner, and upstream cavity) were investigated for three different gap heights (1/2”, 1/4”, and 1/8”) using infrared thermography to study their effects on gap heating and dispersion of the vortex system. Two models were designed to investigate the gap geometries (a cylinder model, and a fin model). The cylinder model provided optical access inside the gap while the fin model allowed the regions of the end wall outside of the gap to be viewed. The models were preheated to an initial temperature of 75oC and 90oC and cooled using M = 1.8 and M = 2.9 flow. Stanton profiles were calculated using the infrared temperature data along with a code that solved for instantaneous heat flux (QCALC) which was provided by Purdue. The round geometry showed merit for reducing the heat flux within the gap for large gap heights by dispersing the corner vortex, which is associated with elevated heating. A side effect of this is an enhanced primary vortex which impacts a larger area outside of the gap. When the gap height is decreased, the round corner performs at best like the right-angle geometry. This suggests that smaller gap heights are preferred. They allow less flow into gap reducing the heat transfer. At smaller gap heights, a right-angle corner was shown to cause either Stanton values lower than or equal to the rounded corner along the centerline. This suggests a right-angle geometry is the better choice for small gap heights. If large gaps heights are required, rounding the torque-tube base could reduce the localized heating along the centerline near the corner. The cavity geometry performed poorly across the board. Any promise it showed at decreasing Stanton values were offset by the increased heating all along the length of the cavity