An experimental investigation on focussing of weak shock waves in air

The behavior of focussing weak shock waves was experimentally investigated with a view to observe and understand the processes occurring near the focus, especially the processes that control the maximum amplitude. Concave reflectors are used against the endwall of a large 17 inch diameter shock tube, to focus the plane incident shock. Reflectors producing line and point foci, and cusped and smooth caustics were examined for incident shock Mach numbers ranging between 1.005 to 1.5. The flowfield is observed with spark shadowgraphs to visualize the motion of various wavefronts. Pressure histories measured at various points in the flow with miniature piezoelectric gauges provide additional information about the various processes occurring near the focus.