Shock Wave Modification by a Plasma Spike: Experiment and Theory

Abstract

Experiments were conducted in a Mach 2.5 wind tunnel to explore the modification effect on the shock wave structure by a plasma spike generated by an on-board 60Hz electric discharge in front of a 60° cone-shaped model, which is used as a shock wave generator. 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 shock into a classic highly curved bow shock structure, which also appears in diffused form. Experimental results exclude the heating effect as a possible cause of the observed shock wave modification. A theory using a wedge model as the shock generator is developed to introduce a non-heating mechanism responsible for the observed plasma effect on shock waves. Analysis shows that the plasma spike can effectively deflect the incoming flow before the flow reaches the wedge consequently the shock structure in the interaction region is modified from an oblique one to a slightly curved one. The shock front moves upstream with a larger shock angle, consistent with the experimental results.