On shock waves in a confined reflector

Abstract

The main objective of the present work is to carry out experimental studies concerning generation of polygonal-shaped shock waves in a procedure introduced by Apazidis and Lesser [N. Apazidis, M.B. Lesser, On generation and convergence of polygonal-shaped shock waves, J. Fluid Mech. 309 (1996) 301–309]. In this procedure an expanding circular cylindrical shock wave with constant Mach number distribution is generated at the center of a confined air-filled chamber. The chamber boundary has the form of a slightly perturbed circle. The shock reflects off the boundary and converges in the inner of the chamber into a polygonal shape. For this experimental study, an air-filled chamber was designed and manufactured. Shocks were generated by means of an electric discharge. A schlieren system with camera and delayed flash device, was used in order to visualize the process. Equipment for time control and measuring was also used. The experimental results of the current investigation confirmed the theoretical predictions obtained in earlier studies of similar problems. The major new result showed that it is possible to generate polygonal-shaped shocks with sharp corners and plane sides by means of reflection from a smooth boundary. The shock strength was estimated to M=1.1 and the observed shock form confirmed the earlier theoretical predictions. The proposed experimental procedure showed to be a simple, stable, repeatable and reliable method to produce highly symmetrical polygonal-shaped converging shocks.