Experimental Studies of Shock Diffraction

Diffraction of a normal shock wave has been the subject of numerous studies, dating back work of Whitham [1]. A large number of the complex flow features present were highlighted in the well known work by Skews [2]. Fig. 1 shows the flow features behind a strong shock diffracting around a sharp corner. Skews showed that for angles greater than 75o the flow features become independent of the corner angle making the flow is solely dependent on incident shock Mach number, M1. For incident shock Mach numbers greater than Mi = 2, the flow features resemble those seen in Fig. 1; however, for Mach numbers Mi < 2.0 the flow does not expand to supersonic speeds according to the theory given by Sun and Takayama [3] meaning that there is no secondary shock (Ss) as the flow in region 2 can decelerate without shock waves. As the incident shock (I) diffracts around the corner, a slipstream (SL) is formed because the flow cannot follow the contour of the wall and therefore separates. The slipstream rolls up into a vortex (V) which begins to slowly propagate downstream. Application of Schlieren imaging to this type of flow is relatively common and reasonably straightforward. However, the application of PIV to this type of problem, which incorporates both compressible and unsteady flow, has only been tried on a handful of occasions [4][5][6] mainly involving vortex propagation. This study will aim to capture the moving shock and the phenomena associated with its diffraction.