Numerical investigations into the transient behaviour of a model pump-turbine during load rejection process

Three-dimensional numerical simulations were carried out to investigate the transient behaviours of a model pump-turbine during load rejection processes. The influences of guide-vane closing schemes on the transient evolutions of flow patterns, pressure fluctuations and runner forces were investigated. The results show that when the trajectory of operating point moves through the region with backflows occurring at the hub side of the runner inlet, pressure fluctuations in the vane-less space and unstable radial force on the runner become severe, which are duo to the enhanced momentum exchange between the sound inflow and stalled backflows. Furthermore, closing the guide-vanes more quickly in the first reach of piecewise procedures can effectively suppress the development of backflows at the initial stage of load rejection process, resulting in significant decreases of pressure fluctuations and runner forces.