Refraction of a shock wave at an air—water interface

The problem of a shock wave refracting at an air/water interface is considered as an example of a typical refraction of a shock passing from a medium of lower impedance to one of substantially higher impedance. Relatively little work on the subject has been reported in the open literature. This may be due to the fact that only a small amount of the energy associated with the shock in the air enters the water, so there is not much engineering interest in the effects in the water. In spite of this, there are some interesting phenomena. This paper reports on experiments on a plane air-water interface in a shock tube, together with associated numerical studies using the TVD method. Excellent agreement was obtained. Application to a height-of-burst explosion in air over water is also reported. In this case the experiments were done with small lead azide charges. This work was supported by analytical studies from which an unexpected result was reported: that the pressure tended to increase with water depth. There was some experimental evidence to support this result.