Pressure-Wave Propagation in Cavitation Cloud and Its Image Analysis (Cavitating Water-Jet Impinging on Solid Wall)

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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 collapse of an unsteady cavitation cloud when a cavitating water jet impinges against solid wall. In the present experiment, cavitation clouds are observed to investigate the details such as impinging and collapsing behaviors using a constrained-type test section. The present purpose is to investigate about the behavior of cavitating water jet in the near impinging wall region and the relation of cavitation cloud collapse with pressure wave formation as well as the propagation of pressure wave. 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 clouds. 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) cloud collapse causes a pressure wave which propagates toward the surrounding area and as a result causes secondary local collapses in a chain-reaction manner.