Shock stand-off distance visualization in hypersonic shock tunnel using electrical discharge technique

Visualization of the detached shock wave that forms ahead of a blunt body flying at hypersonic Mach number using electrical discharge technique is a simple and convenient technique to measure the stand-off distance experimentally in an hypersonic shock tunnel. In this technique a thin sheet of electrical discharge generated between a point electrode attached to the wall of the test section and a line electrode embedded on the model surface reveals the position of the shock wave around the body in hypersonic flow. In this paper we present the details of this technique and sample results obtained for typical body shapes tested in HST2 shock tunnel at a freestream Mach number of 5.75. The detached shock waves in front of the test models are clearly visualized using this technique. The shock stand-off distance estimated based on the numerical results for a large angle blunt cone obtained using a commercial CFD code match well with the experimentally measured value. These results clearly demonstrate the suitability of the electrical discharge technique for visualizing the flowfields in hypersonic testing facilities having very short test time