Numerical and experimental study on the hydrodynamic characteristics of the hub vortex at the nozzle of a water jet propulsion pump unit

Abstract

The generation and development of hub vortices in the wake of water jet propulsion pump units lead to energy loss and reductions in propulsion efficiency and hydrodynamic performance. In this study, a numerical scheme is developed to simulate the internal and external flow fields of water jet propulsion pump units, and visual experiments are used to verify the numerical results. The hub vortices are observed to develop from the vortex structure at the tail edge of the guide vane and vortex clusters on both sides of the guide cone tip. The vortex structure at the tail edge of the guide vane is generated by the pressure gradient in this region. As the axial distance increases, this structure gradually becomes concentrated around the hub vortex position and vorticity loss occurs. The radius of the hub vortex gradually increases with increasing axial distance at the nozzle section. The rotational speed of the periphery of the hub vortex progressively affects the flow velocity in the nozzle channel.