Experiments and numerical simulations of a flow instability in a low-specific-speed pump-turbine

In order to clarify the mechanism of the fluid oscillation, which occurs for a shut-down sequence of a pump-turbine, the experiment and numerical simulation of the pump-turbine were performed. The pressure fluctuation is measured at inlet, outlet and four points between the runner and guide vanes. Parameters are flow rate, rotating speed and guide vane opening ratio. Results show that the characteristic curve shows so-called "S-shaped" and the pressure oscillation occurs in the "S-shaped" region.