Experimental study and plasma control of an unstarting supersonic flow

The unstart induced by a transverse jet in a Mach 4.7 model inlet flow is visualized by planar laser scattering from condensed CO₂ particles at low freestream static pressure (1kPa) and temperature (60K) for various boundary layer conditions. We find that the formation of an unstart shock is initiated on the relatively thick boundary layer side and its structure depends on the boundary layer conditions. The pseudo-shock or oblique shocks that precede unstart propagate upstream in symmetric and asymmetric boundary layer conditions, respectively. It is found that the pseudo-shock has a quasi-stationary mode resulting in longer overall unstart events. The results suggest that the unstart process can be influenced and possibly delayed by the control of the boundary layer conditions. In this paper, we present preliminary results on boundary layer manipulation of an unstarting supersonic flow using Dielectric Barrier Discharge (DBD) actuation. We find that the asymmetric boundary layer condition that generally leads to the formation and propagation of an oblique unstart shock, when actuated, can be transformed the flow to resemble that of a symmetric condition which leads to the generation of a pseudo-shock, extending the unstart duration by 22 %.