Control of Shock Train Structure in Isolator by Electrical Discharge

Quasi-direct-current near-wall filamentary electrical discharges were used to control Mach 2 shock trains within two different geometries. Experiments were conducted over variable flow stagnation conditions and downstream blockage settings. During flow control, the shock train leading edge was observed to transition from a symmetric shock to an asymmetric shock with a reduced normal portion. The control-side leg of the shock train was biased upstream from the opposite leg, becoming anchored at the discharge electrodes. Whether the leg opposite the control-side wall was repositioned upstream or downstream depended on flowpath geometry. Electrical discharge control significantly reduced the pressure gradient through the isolator, which resulted in a decrease in exit pressure. High-speed pressure sensors were used to study the local flowfield at the actuator location. The flow control effectively stabilized the pressure gradient along the isolator wall via the removal of discrete shocks. A continuous wavelet transform analysis revealed that flow control reduced high-amplitude broadband pressure fluctuations while introducing a flowpath-specific 100 Hz mode. Finally, a quasi-one-dimensional model was constructed and indicated that plasma-based control enables a reduction in total pressure losses depending on shock train length.