Dynamics of an Elongated Bubble During Collapse

Abstract

An analytical model is presented to describe the collapse of an elongated bubble, which appears in the core of a cavitating vortex. The flow field is assumed to be irrotational, due to a sink line. The kinematic and dynamic conditions are applied only at the tip and in the middle of the bubble surface. This simplified theory must retain losses of mechanical energy near the tips of the bubble, which are due to a microjet. In order to check the validity of this model, the irrotational flow equations have been solved numerically by using a panel method; the numerical results agree with the analytical ones and confirm the existence of the microjet at the tip. The agreement with experimental results is also good. For very slender bubbles the speed near the tips becomes very large, and this may be cause of cavitation damage. A simplified approach is proposed to explain the flow in the microjet.