Study on the Suppression of Cavitation Instability in a Two-Stage Inducer

The present study describes a two-stage inducer that has a pre- or first-stage inducer at the inlet of the primary or second-stage inducer to suppress cavitation instability and improve suction performance. The first-stage inducer modifies the inlet flow conditions of the following second-stage inducer to directly control cavity development. Experimental and numerical investigations were carried out for two different types of the first-stage inducers to characterize their cavitation suppression performance for various flow rates and inlet pressure conditions. The effects of relative angular configuration between two stages were also examined. The experiments showed that the scheme of the two-stage inducer can significantly improve the cavitation performance for a wide range of flow coefficients. But the extent of the improvement depended on flow coefficients and relative angular distances. The analysis of cavitation instability showed that the first-stage inducer suppressed cavitation surge effectively. Furthermore, asymmetric cavitation occurred over a smaller region and with lower intensity, indicating that there is an optimal relative angular distance to suppress asymmetric cavitation. Cavitating flow was simulated to explain the suppression mechanism of cavitation instability in the two-stage scheme. The simulated results of cavity growth and blade loading revealed that the reduction of the cavity closure thickness at the throat position of blade channel has a critical role in suppressing asymmetric cavitation. [PUBLICATION ABSTRACT]