NUMERICAL INVESTIGATION OF PUMP-TURBINES WITH DIFFERENT BLADES AT PUMP CONDITIONS

The undesirable performance of a positive slope curve usually appears for pump-turbines running as pumps at a low flow rate. The inner flow feature of pump-turbines with 6- and 7-blades runner is studied by both steady and unsteady simulations at pump conditions. According to the steady simulation investigation, obviously back flow vortex is found in the runner passage at the low flow rate zone where the positive slope curve forms. The flow rate at which the instable flow pattern happens of 6-blades runner is smaller than that of 7-blades one. By the unsteady simulation, at the low flow rate zone similar to the steady calculations and the tested data, a rotating stall with four rotating cells can be viewed by significant dynamic post-processing, whose rotation speed is much slower than that of the runner. Therefore, the back flow vortex of steady simulation and rotating stall of unsteady simulation can be used to investigate the runner quality at design stage.