Abstract
Some important points remain unsolved though it is considered that the instability can be divided into two categories such as a mechanism peculiar to cavitation and the other caused by system factors such as surge. The mechanism of cavitation instability is summarized and explained using several results of the authors' group. In the present study a high speed water jet with cavitation is mainly investigated as a typical cloud cavitation phenomenon. Especially an image analysis method based on frame difference from high speed video observation is applied for three kinds of cavitating nozzle flows to catch the motion of pressure waves which is one of the key factors to solve the reentrant motion mechanism. As a result, the cavitation instability mechanism can be explained with the use of the present image analysis method.
