INVESTIGATION OF SUBSTRUCTURE HEATING ON CRACKED ABLATIVE HEAT SHIELDS.
NAVAL ORDNANCE LAB WHITE OAK MD
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An experimental program was carried out to study the effect of cracks in an ablative heat shield on the substructure heating. The test conditions involved stagnation pressures of 20 to 30 atmospheres, temperatures of 4000 to 9000R, and Mach numbers of 2.3 and 3. The models, made of teflon, has transverse and longitudinal cracks machined into the surface. They were instrumented for pressure, temperature, heat transfer and skin-friction measurements. The cracks were found to have pronounced effects on the ablative behavior. The heating is moderate under a laminar boundary layer, but can be catastrophic when the boundary layer is turbulent, depending upon the size and direction of the crack. The results for the transverse cracks were compared with an available analytical prediction. Ablation was found to reduce the wall shear stress by 40 percent or more. Author
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