Numerical Prediction of Cavitation Inception in Centrifugal Impellers

Cavitation is a fundamental issue in pump design since it yields significant decrease of performances and pump life, damaging impeller surfaces and triggering harmful flow instabilities. This topic is usually addressed through costly experimental tests. The aim of this paper is to assess numerical methodologies for the correct evaluation and prediction of the cavitation inception in centrifugal impellers during the design phase. Preliminary analyses were performed to individuate the most promising approach by using two cavitation models on a 2D test case representing the NACA 0009 hydrofoil. Then, two CFD approaches were considered for the evaluation of the NPSHr in actual pumps. RANS two-phase calculations including the selected cavitation model were performed on a geometry provided by WEIR Gabbioneta srl. Monophase simulations have been performed as well and an in-house heuristic model has been proposed to evaluate the NPSHr curve from a non cavitating pressure field. The heuristic post-processor has been tuned using both the two-phase and the monophase data, and validated using the available experimental values provided by WEIR Gabbioneta srl.