The Plasma Mitigation of the Shock Waves: Experiment and Theory

Summary form only given. Experiments were conducted in a Mach 2.5 wind tunnel to explore the plasma effect on the shock wave. An on-board 60 Hz electric discharge is applied to generate a plasma spike in front of a 60deg cone-shaped shock wave generator in a Mach 2.5 supersonic flow. Due to cyclic nature of the generated plasma an unsteady shock motion during one discharge period was observed. The pronounced influence of plasma on the shock structure is clearly demonstrated by the result, at the peak of the discharge, showing a transformation of the shock from a well defined attached oblique shock into a curved shock structure. The shock front moves upstream with a larger shock angle and appears in diffused form. Experimental results indicate that, in order to give rise significant effect on shock waves, plasma has to be generated in the region upstream of the baseline shock front and has to have a symmetrical spatial distribution with respect to the axis of the model. Experimental results also exclude the heating effect as a possible cause of the observed shock wave mitigation. Using a symmetrical wedge model as the shock generator and assuming a symmetrically distributed plasma spike located at a small distance in front of the model, a theory is introduced to explain the observed plasma effect on shock waves by a non-heating mechanism. Analysis shows that the plasma spike can effectively deflect the incoming flow before the flow reaches the wedge; consequently the shock front moves upstream with a larger shock angle and the shock structure is also modified from an oblique one to a slightly curved one, consistent with the experimental results