Numerical Investigation of Impeller Leading-edge Profiling on Vortex Suppression and Performance Enhancement in a Pump-as-turbine

Abstract

Centrifugal pumps operating as turbines (PAT) offer a cost-effective solution for micro-hydro power plants. However, their hydraulic performance is compromised by flow separation at the impeller’s outer diameter. This study conducted a transient numerical analysis to evaluate the hydrodynamic effects of modifying sharp blade edges into rounded profiles. The mesh structure setup, consisting of Poly-Hexcore with a k-ω turbulence model using the Computational Fluid Dynamics (CFD) in ANSYS Fluent with Meshing solver, was validated based on experimental data and applied across a wide operational range (27.75 L/s ≤ Q ≤ 65.0 L/s). Performance characteristic analysis shows that rounded blades significantly improve energy extraction. At the PAT best efficiency point (BEP), efficiency increased from 65.46% to 68.79%, and the power output of the mechanical shaft increased by 29.96%. Physical evaluation of pressure contours and velocity flow line topologies validated these benefits. An impeller with sharp blades causes severe flow separation and generates turbulent vortices that obstruct flow on the suction side of the blades. Conversely, an impeller with rounded blades successfully suppresses vortex formation and maintains a flow topology that adheres to the blade curvature, ensuring uniform momentum transfer to the rotor.