Drag and total pressure distributions in scramjet engines at Mach 8 flight

To complement our hydrogen-fueled scramjet engine research, aerodynamic tests were conducted by using one-fifth-subscaled (0.44 in-long) models in Mach 6.7 freestream conditions. The drag of the engines was estimated by using a force balance and pressure distributions on the internal wall to separate the internal drag and the external drag. The swept shock wave theory yielded the air capture ratio and the additive drag due to the spilled flow. Two methods for drag evaluation, based on force balance measurement and on wall pressure Pw measurement, were compared to examine their accuracies. They enable identifying the origins of pressure and friction drags. It was found that frictional drag constituted more than half of the internal drag of engines and that the pressure recovery across the engine decreased to about 4% when large struts were installed in the inlets. The fundamental principles and the experimental validation of the methods for evaluating the internal drag in scramjet engines with large struts is reported.