Effect of Sides-Spillage from Airframe on Scramjet Engine Performance

Abstract

Pre-compression by the windward surface of the aerospace plane is necessary for scramjet operation. However, this pre-compression causes spillge from the high-pressure windward surface toward the sides of the plane. In rder to examine the effects of this side-spillage, the performance of a scramjet engine was evaluated using a 1-D (one dimensional) flow model, and payload to the low earth orbit estimated using an aerospace plane flight simulation. Prior to the simulation, tests with scramjet inlet models were conducted in a Mach 4 wind tunnel to identify the primary features of the side-spillage to assist in the simulation. The models were inclined from the flow direction to simulate the skewed flow near the side of the plane during side-spillage, and the experiments proved that the aerodynamic performance of the inlet was not affected by the inclination for the entrance Mach number given to the models. However, the mass capture ratio decreased due to reduction in the density of airflow as a results of the expansion. In the numerical estimate, side-spillage was modeled not to reduce the performance of the inlet, but to reduce mass flow to the inlet. The resulting decrease in airflow delivered to the engine due to spillage reduced thrust by 15 percent, while the corresponding payload decreased around 60 percent. Side fences were effective in preventing spillage.