Control of mean separation in shock boundary layer interaction using pulsed plasma jets

The current study investigates the use of pulsed plasma jets (spark jets) to reduce the separation induced by shock wave-boundary layer interaction generated by a 20 ∘ compression ramp in a Mach 3 flow with a Reynolds number of 5,400, based on the undisturbed boundary layer momentum thickness. Surface oil streak visualization is used in a parametric study to determine the optimum pulsing frequency of the jet, the optimum distance of the jet from the compression corner, and the optimum configuration of the jets. Several 3-jet actuator configurations are tested, including those where the jets are pitched, and pitched and skewed. The jet pulsing frequency is varied between 2 and 4 kHz, corresponding to a Strouhal number based on separation length of 0.012 and 0.023. Particle image velocimetry is used to characterize the effect that the actuators have on the reattached boundary layer profile on the ramp surface. Results show that plasma jets pitched at 20 ∘ from the wall, and pulsed at a Strouhal number of 0.018, can reduce the distance between the separation line and the compression ramp corner by up to 40 % and increase the integrated momentum in the downstream reattached boundary layer, albeit with a concomitant increase in the shape factor.