Tip Clearance Effects on Cavitation Evolution and Head Breakdown in Turbopump Inducer

Abstract

The objectives of the present study were to investigate the effects of tip clearance on cavitation performance and flow characteristics in a turbopump inducer by using computational fluid dynamics. Three different tip clearances were analyzed under design (Q(d)) and off-design (0.8Q(d) and 1.2Q(d)) cavitating conditions. The Rayleigh-Plesset model was implemented in ANSYS CFX 13.0 by using rate equation controlling vapor generation and condensation in the context of two-phase one-fluid analysis to calculate the cavitating flows. Numerical results in this study were validated by comparison with experimental results for suction performance. Cavitation inception occurs at the leading edge of the blade tip. For high cavitation numbers, the static pressure under cavitating conditions is almost the same as that under noncavitating conditions because tip vortex cavitation and tip leakage vortex cavitation do not affect the flow significantly or deteriorate the overall performance. Tip vortex cavitation and tip leakage vortex cavitation tend to become large for small tip clearances at the low flow rate. However, long blade cavitation develops for large tip clearances and obstructs the throat between two adjacent blades; such cavitation results in head breakdown at high cavitation numbers for large tip clearances. Further, at the high flow rate, head breakdown occurs at high cavitation numbers due to abrupt obstruction at the throat by blade cavitation on the pressure side as well as on the suction side.