Flow characteristics analysis of an extra–high–head pump–turbine with splitter–blades under high pressure-pulsation condition

The new energy system aims to provide reliable, affordable and sustainable energy, and ultimately achieve carbon neutrality. But the unstable renewable energy sources including wind and solar increase the risk to the grid and the power system. The pumped–storage power stations are a good solution to compensate then fluctuating energy and can increase the robustness of the grid. However, the pump–turbine units also suffer from high pressure-pulsations, especially at off-design operating conditions. The flow inside the unit under off-design conditions has very complex hydrodynamic characteristics and generates significant stresses in the prototype pump–turbine units. This work investigates the transient flow characteristics of an extra– high–head pump–turbine prototype with splitter– blades with unsteady CFD simulations. The results show that the pressure-pulsation caused by rotor-stator interaction is the dominant pressure-excitation to the pump– turbine prototype. The excitation frequency is strongly related to the blade number in the rotating frame and the guide-vane number in the non- rotating frame, as well as the rotating frequency of the unit. The flow characteristics at a high pressure-pulsation working condition are extremely complex and unstable. It reduces the efficiencies of the pump–turbine prototype and can generate severe vibrations and stresses on the structural component of the unit. The calculated results of this research can be applied to the structural model to invest in the dynamic characteristics of the pump–turbine unit in the next step.