Effect of Ingested Boundary Layer on Scramjet Engines' Thrust and Combustion Characteristics

Abstract

National Aerospace Lab. of Japan has been testing sidewall compression-type scramjet engines at Mach 8 flight condition since 1998. Like typical scramjet engines, our engines also ingest a thick boundary layer developed along facility nozzle surface to simulate an air flow that these engines on the vehicles will take in. Although this layer supports fuel-mixing and - combustion in the engines, it is also an origin of flow separation at the inlet section and engine-unstarting. Therefore, controlling this boundary layer is one of the essential techniques for the scramjet engines. With two engines that have a strut or a rampblock, we experimentally inspected this boundary layer effect on their performances, i.e., thrust, Isp, and their inlet's starting/unstarting. Engines are tested in two different types of incoming air flows with a fully-developed boundary layer, with an inviscid region of the layer. Based on these experimental data, we discuss the effect of the ingested boundary layer and evaluate the contribution of the boundary layer to engine's total performance. The engine with a strut affects strongly the boundary layer in its limit of starting and thrust performance, but the engine with a rampblock does not. This difference is caused by the upstream influence distance of pressure distribution, which is a function of the ingested boundary layer.