Numerical Investigation of Inner Flow Characteristics of a Prototype Pump Turbine with a Single Pier in Draft Tube at Part Load Conditions

Abstract

Pump turbines operate under various off-design conditions, resulting in complex internal flow patterns. This study employs Reynolds-averaged Navier–Stokes (RANS) numerical methods to investigate the flow characteristics of a prototype pump turbine with a single draft tube pier in turbine mode, and then, the flow characteristics inside the draft tube are discussed with emphasis. Asymmetry between the pier-divided draft tube passage flows is inevitable due to the elbow section’s curvature. Most of the fluid flows out of one passage, while vortex motion dominates the interior of the other one, resulting in completely different pressure fluctuation characteristics for the two flow passages. The large-flow passage is mainly characterized by the wide band in the frequency domain, corresponding to the recirculation zone, while some of the measured points in the low-discharge passage exhibit frequency splitting under kinematic progression. Further analysis demonstrates a low-frequency peak corresponding to the complementary shape between the vortex rope and the recirculation zone. This work elucidates the effects of the pier on the flow behavior and pressure fluctuation characteristics inside the draft tube and fills the research gap on piers in the field of pump turbines.