Fast-Acting Boundary-Layer Suction Control of Unstarting Flows in an Ethylene-Fueled Dual-Mode Scramjet

Abstract

The boundary-layer suction control of unstarting flows in an ethylene-fueled dual-mode scramjet was experimentally investigated in the present study. A model scramjet with a rectangular cross-section was tested in Mach 4.5 high-enthalpy freestreams, and an ethylene jet was injected into the model to trigger inlet unstart. Wall-pressure measurements and electronically excited CH (CH*) chemiluminescence imaging were performed to characterize the behavior of the unstarting flows. The overall equivalence ratio in the engine was increased to induce inlet unstart, which was detected based on sudden drops in the pressure, a reduction in power of high-frequency pressure fluctuations, and abnormal CH* emissions in the combustion zone. Two perforated plates with suction holes were installed on the top and one side of the internal surface of the model, and boundary-layer suction control was activated using fast-acting solenoid valves at designated times. Suction from each plate could extract approximately 1% of the freestream flow. Single- and double-plate suction control was also tested under various overall equivalence ratios, with boundary-layer suction found to significantly delay inlet unstart under marginal unstart conditions.