Vortex-induced energy loss of a mixed-flow waterjet pump under different operating conditions

Mixed-flow waterjet pumps (M-FWPs) are core units of high-speed ship power propulsion. When operated under non-optimal operating conditions, the unstable flow generated in the flow passage leads to a reduction in pump efficiency. This article investigates the energy loss mechanism of M-FWPs under different operating conditions through entropy production theory based on numerical simulations. The analyses of the simulation data show that the turbulence dissipation (EPTD) makes the dominant contribution to the entropy production rate. By comparing the correlations of velocity gradient, vorticity, and turbulent kinetic energy (TKE) with the EPTD, it is discovered that under non-optimal operating conditions, the inflow angle at the impeller inlet does not match the blade inlet angle at the leading edge of the blade, resulting in unsteady flow structures such as flow separation and large-scale vortices. The increase in vorticity and TKE caused by these unsteady structures ultimately causes the generation of turbulent entropy. Further examination of the enstrophy transport equation indicates that the relative vortex generation term plays a dominant role in the development of the unsteady flow in the flow passage