Effect of Tip Clearance on the Cavitation Performance of a Turbopump Inducer

The characteristics of steady and unsteady cavitation in a two-bladed inducer for a turbopump are investigated. A helical inducer with inlet tip blade angle of 7.8 deg and a tip solidity of 2.7 is tested using water as a working fluid. To determine the effect of tip clearance on the inducer performance, a series of experiments is conducted at three different tip clearances. As the tip clearance increases, the inducer head decreases and the critical cavitation number increases. Unsteady pressure measurements at the inducer inlet indicate the existence of attached cavitation and cavitation surge, but no rotating cavitation in the test inducer. Attached cavitation and cavitation surge appear for all three cases of tip clearance. The cell number and propagation speed of the attached cavitation are determined through a cross-correlation analysis. In the case of attached cavitation, one cell rotates at the same speed as that of the inducer. In addition, the surge frequency decreases with a decrease in the cavitation number, and the ratio of surge frequency to inducer rotational frequency is found to range from 0.07 to 0.20.