Application of the Full Cavitation Model to Pumps and Inducers

Abstract

A new ＂full cavitation model＂ has been recently developed for performance predictions of engineering equipment under cavitating flow conditions. A vapor transport equation is used for the vapor phase and it is coupled with the turbulent N-S equations. The reduced Rayleigh-Plesset equations are used to account for bubble formation and to derive the time-mean phase-change rates utilizing the local pressures and characteristic velocities. Effects of turbulent fluctuations and noncondensable gases are also included to make the model complete. The model has been incorporated into an advanced finite-volume, pressure-based, commercial CFD code (CFD - ACE +) that uses unstructured/hybrid grids to integrate the N-S equations. Full model details are being published separately. Presented here are simulations of cavitating flows in three types of machines: water jet propulsion axial pump, a centrifugal water pump, and an inducer from a LOX turbo pump. The results show cavitation zones on the leading edgesuction side of each of the machines as expected. Simulations at different suction specific speeds were performed for the waterjet pump and the inducer and showed the proper trends of changes in cavity strength and sizes. All the test cases with cavitation show plausible results (no negative pressures, and good convergence characteristics). Computations on the waterjet pump for different noncondensible gas concentrations showed sizeable changes in the pump head developed.