Rotating Behavior Observation of Cavitation in Inducer with Suction Axi-Asymmetrical Plate

Abstract

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. In operating condition at partial flow rate and extremely low suction pressure, cavitation surge oscillation occurs and the stable operating range becomes narrower. It has been found from previous experimental study of authors that the cavitation surge oscillation with low frequency occurs with close relation between the inlet back-flow cavitation and the growth of blade cavity to the throat section of blade passage. One method, which is to install an axi-asymmetrical plate upstream of inducer, has been proposed to suppress the cavitation surge oscillation. It is considered conceptually to be the suppression mechanism of oscillation that the inlet flow distortion by suction axi-asymmetric plate avoids the flow at all throat sections getting unstable simultaneously. In the present study, in order to clarify the suppression mechanism experimentally observation of rotating behavior of cavitation in the inducer is performed with distributing multi cameras circumferentially, recording simultaneously and arranging the pictures to show the entire view of the flow around the linear cascade. The observed cavitation behavior is utilized for discussion on the suppression mechanism of oscillation with other measuring results such as casing wall pressure distribution and velocity distributions with LDV. Then the suppression mechanism of oscillation by installing the axi-asymmetrical plate will be clarified in more details.