Comparative numerical studies for the flow energy dissipation features in a pump-turbine in pump mode and turbine mode

Abstract

Reduction of flow energy dissipation (FED) in pump-turbine is important in improving the energy conversion efficiency of pumped storage power station. By eliminating obvious undesirable flow regimes, the efficiency of modern pump-turbines is higher than 90% in both pump and turbine modes. However, the further efficiency improvement is difficult because it is hard to visualizing, locating and quantifying FED. Based on Computational Fluid Dynamics (CFD) and thermodynamics evaluation, the irreversible FED features in a reversible pump-turbine is comparatively analyzed in pump mode and turbine mode. By analyzing different off-wall distance zones, the near-wall (<2 mm) and far-away (>10 mm) regions are found with high FED. By comparing different components, runner is found as the main FED source (proportion >50%). The stators downstream to runner (vanes in pump mode and draft tube in turbine mode) has also high FED due to local vortical flow. FED in pump-turbine is found with different sub-types. The viscosity-dominated type is found with local increasing of turbulence kinetic energy and temperature. The striking-dominated type is found with local sudden velocity reduction. Targeted elimination of vortical flow, reduction of surface-roughness and improvement of geometry-flow adaptability will be effective in the future high-efficiency design of reversible pump-turbines.