Shock Wave Pressures in Water Produced by Impact of Small Spheres

Abstract

Microsecond spark shadowgrams were made showing shock waves in water. The waves were produced by spheres ${\frac{1}{8}}^{\prime \prime }$ to ${\frac{1}{4}}^{\prime \prime }$ in diameter when they struck a water surface with velocities between 2000 and 4800 ft./sec. Pressures in the wave were calculated from measurements of the absence-of-light band. The pressure was found to be greatest at a point directly ahead of the sphere and to fall off to normal pressures near the surface. The waves of large pressures were observed to travel faster than a sound wave and to have velocities in accordance with the measured pressure. Because of the varying strength over the wave front, the waves have the shape of a semi-ellipse. When the entrance velocity $V$ and projection area of the sphere were varied it was found that the pressure varied as $V^{2.17}$. It also increased linearly with the projection area of the sphere. The pressures were shown to be in fair agreement with those calculated from the compression of the water at the sphere's entrance; in the calculation an arbitrary loss of water in the splash was assumed.