Shock Focusing Across a Layer Between Two Kinds of Liquid

Abstract

We have been studying shock focusing in water by means of a reflector, shaped as a semi-ellipsoid; an underwater spark discharge is used as a source of spherical shock waves. This is the case when the medium in which the shock propagates consists of one kind of liquid, water. If the medium consists of two kinds of liquid that have different acoustic characteristics respectively, a semi-ellipsoid cannot be used, because a shock wave that obliquely passes through the layer between those liquids refracts there and cannot converge. In this paper, a method is proposed of modifying the semi-ellipsoid to make a spherical shock wave produced in water converge in silicone oil across the layer between those liquids, taking into consideration the refraction there. Evidence that the shock wave is focused by the reflector modified as above is shown on Schlieren photographs. Besides, the pressure amplitudes at some points on the axis of the modified semi-ellipsoid are measured with a pressure probe and the results confirm that it is possible to make a spherical shock wave converge across the layer between water and silicone oil by the modified semi-ellipsoid.