Transient Effect of Passive Bleed Slots on a Propagating Shock Train

An experimental study was conducted to evaluate the flow control effect of passive wall slots on a Mach 2 shock train. High-speed pressure measurements and focusing schlieren imaging captured the steady and unsteady flow behavior over variations in the on-design slot condition, downstream blockage depth, and transient nitrogen injection condition. The pressure field and unsteady pressure levels were found to depend strongly on the backpressure value and slot condition. Comparing the baseline configuration to the slot-installed configuration revealed that passive slots anchored the shock train leading edge, increased the Mach stem height, and increased the associated pressure rise. The shock train was anchored by the slots at backpressure conditions that unstarted the baseline flowpath. Transient experiments showed that the baseline STLE propagated upstream at a nearly constant rate, while slot-in cases exhibited propagation characteristics dependent to the on-design slot condition. These results highlight how slots influence the shock train motion, pressure distribution, and pressure field oscillations in high-speed air-breathing engines.