Response of Internal Flowfield to Downstream Pressure Oscillation in a Scramjet Engine

Abstract

ABSTRACT The response of the internal flowfield to back pressure oscillation in a scramjet engine is studied numerically. The physical domain of interest includes both the isolator and combustor. The theoretical formulation is based on the full conservation equations in three dimensions. Turbulence closure is achieved using the SST model to improve the prediction of shear stress under adverse pressure gradient. As part of the downstream boundary condition, a high pressure is imposed to simulate the pressure condition in the situation with combustion. Periodic pressure oscillations in the frequency range of 376–1128 Hz are also imposed to mimic flow oscillations caused by combustion instability. The downstream disturbance is found to influence the supersonic core flow in the isolator through separated boundary layers. A shock train is initiated from corner separation shocks, and X-type shocks take place to adjust the pressure between the core flow and the separation bubble on the wall. When the frequency of back pressure oscillation is lower, the shock front fluctuates over a larger displacement. The shock front acceleration is correlated to the rate of change of pressure in the separation bubble on the wall, which increases with increasing back pressure frequency. However, when the oscillation increases to 1128 Hz, the rate of change of pressure in the separation bubble decreases, resulting in a more stable shock front. The shock train acts as a low-pass filter and damps flow oscillation in the isolator-combustor.