Pressure-wave formation and collapses of cavitation clouds impinging on solid wall in a submerged water jet

Abstract

A high-speed water jet ejected into water forms a cavitating water jet accompanied with cavitation clouds in a periodic manner. A powerful impulsive force can be caused at the collapse of unsteady cavitation clouds at the same time when the cavitating water jet impinges against a solid wall. It is known that this force can be widely used in an industrial field such as cleaning, cutting, and peening. In the present experiment, cavitation clouds are observed to investigate the details such as impinging, dividing and collapsing behaviors using a constrained-type test section as well as an opentype test section. The constrained-type test section is used to quasitwo dimensionally observe the behavior of cavitation clouds in the near impinging wall region. The present purpose is to investigate about the behavior of cavitating water jet in the near impinging wall region as well as the relation of cavitation cloud collapse with the formation of pressure wave, the propagation of pressure wave and the cavitation impact. In order to estimate the high speed phenomena such as rapid and consecutive collapses of cavitation clouds and pressure wave formation, the frame difference method for cavitating flow is used in the present image analysis for cavitation cloud. The usefulness of the method is experimentally verified for the behavior analysis of high speed liquid flow accompanied with growth and collapse of bubbly cloud. As a result it is experimentally found that 1) the present image analysis method based on the frame difference method makes possible to grasp the motion of pressure wave propagation in cavitation cloud, 2) local cloud collapse causes a pressure wave which propagates toward the surrounding area and as a result causes secondary collapses in a chain-reaction manner, and 3) cavitation clouds on the impinging wall tend to be peripherally located in an annular zone at the final collapsing stage. The existence of the annular cloudy zone can be related to the ring-like cavitation erosion distribution and the chain-reaction-type propagation of cavitation clouds.