Evolution of leading edge hub vortex and energy dissipation in a fish-friendly tubular-flow pump toward low-head hydro storage

In the application of fish-friendly hydraulic machinery, flow instability and energy loss induced by the leading edge hub vortex are key factors limiting hydraulic efficiency and operational stability. In this study, a low-head fish-friendly tubular-pump is selected as the research object. Based on vortex dynamics theory and the vorticity transport equation, numerical simulations are performed to systematically investigate vortex formation and evolution and the associated vortex-induced energy loss. The results show that the vortex originates from the positive attack angle between the incoming flow and the blade angle, which triggers flow blockage and local flow separation near the blade leading edge. The shear layer within the separation region interacts with the low-pressure region on the blade suction surface, driving low-momentum fluid into a three-dimensional spiral motion and ultimately forming a stable vortex structure at the junction between the hub and suction surface. Under different operating conditions, the vortex initially expands radially and then subsequently develops axially. As the flow rate increases, both the turbulent kinetic energy and tangential velocity at the same monitoring location decrease, accompanied by vortex contraction and gradual dissipation. Analysis of the vorticity transport equation reveals that the relative vorticity convection term dominates the zonal vorticity transport. Furthermore, the dominant frequency of the vortex-induced loss is 2.85 Hz, corresponding to the blade passing frequency. These findings provide a vortex-dynamic basis for optimizing leading edge geometry and selecting operating conditions, promoting hydraulic efficiency and operational stability in fish-friendly pumps.