Three dimensional flow simulation of load rejection of a prototype pump-turbine

Abstract

Three dimensional (3D) unsteady, incompressible flows in a pump-turbine during a transient process of load rejection were studied using the computational fluid dynamics method. The dynamic mesh (DM) method and remeshing method combined with non-conformal grid boundaries were applied to simulate the rotation of guide vanes. The fluid coupling and DM method were used to calculate the rotational speed for each time-step. Calculations were performed based on the \( \overline{{v^{2} }} - f \) turbulence model to incorporate the near-wall turbulence anisotropy as well as non-local pressure–strain effects. Results show that \( \overline{{v^{2} }} - f \) model is thought to be suitable to predict characteristics of the transient process during load rejection in a pump-turbine. The transient explicit characteristics, such as the flow-rate, head, torque of the runner, etc., during the process of load rejection are analyzed. Pressure fluctuation was larger in the region close to the runner during the load rejection. Stalls and reverse flow in the runner resulted in the decrease of the torque of runner at turbine mode and turbine-braking mode. Simulation results were also compared and verified by experimental results. 3D simulations can be used instead of experiments to study the influence of inner flow to the external characteristics during transient processes. This calculation was based on a prototype of a pumped storage power station, and the computational method could be used in the fault diagnosis of transient operation.