Mechanism analyses of the unsteady vortical cavitation behaviors for a waterjet pump in a non-uniform inflow

Abstract

The waterjet pump is widely applied in the high-speed marine vessels to exploit various kinds of resources in the vast ocean. The transient cavitating flows in a waterjet pump are numerically investigated under a non-uniform inflow for the purpose of revealing the correlation mechanism between the cavitation and the vorticity diffusion as well as the exited pressure fluctuations. The unsteady numerical simulation is conducted by using the Reynold-Averaged Navier-Stokes (RANS) method coupled with a homogenous cavitation model. Both the hydrodynamic performance and the cavitation performance are well predicted by the present numerical approach when compared with the available experimental data. The cavitation occurrence would cause larger pulsations to the hydrodynamic characteristics and the nonuniformity together with perpendicularity at the impeller inlet plane. As the blade passes through the non-uniform inflow, the instantaneous cavitation dynamics behaviors include the cavity generation, development and extinction, and the dominant frequency corresponds to the impeller rotating frequency. Based on analyses of the boundary vorticity flux, the cavitation is an important mechanism for vorticity diffusion from the blade into the mainstream with the major contributor of the variable density due to cavitation. Furthermore, combined computational and theoretical analysis illustrates that the cavity volume variations would cause the flow-rate fluctuations and the cavity volume acceleration is the major source for the pressure fluctuations inside the mixed-flow waterjet pump.