Various types of cavitation instabilities are considered to occur when steady cavity length becomes longer than 65% of blade spacing in high-speed turbomachinery, such as turbopumps for rocket engine. If we estimate the steady cavitation, the inception of unsteady cavitation could be predicted. Then, we propose an analytical method for the prediction of steady cavitation in turbomachinery under the assumption that stream surface is rotationally symmetric. The analysis on stream surface is performed by a singurality method based on closed cavity model and is combined with the analysis on meridian plane through the circumferentially averaged velocity. The present method is applied for a flat-helical inducer and three-dimensional effects on cavitation are discussed in comparison with the results of the analysis of two-dimensional flow.
