Vibration of Variable Speed Pump-Turbine in Turbine Operating Range: Simulation by CFD+FEM

Abstract

Abstract Variable speed pumped-storage unit can operate efficiently and stably in wide range of power and head through the coordinated control of the rotational speed and guide vanes. The regulation in rotational speed brings about frequency and amplitude changes of pressure pulsations, which further influence the avoidance margin of vibration and the dynamic response of the runner. The vibration characteristics of the variable-speed pump-turbine need to be studied when it runs in the wider operating region. Selecting an actual pumped-storage unit as the subject and using the CFD+FEM coupled simulation method as a tool, we conducted three-dimensional pump-turbine vibration simulations and analyse the flow patterns, pressure pulsations, and runner vibration characteristics of several typical operating points in turbine mode. The study focused on the variation laws of pressure pulsations and dynamic stresses when rotational speed is regulated. Comparison with the results for the constant speed unit under the corresponding working conditions was conducted. It is shown that the variable speed operation can effectively avoid the severe vibration conditions that the constant speed unit encounters; the amplitudes of pressure pulsations and dynamic stresses of the runner are small at low rotational speed; in the condition of high speed, low head, and small load, the vibration is the most obvious. This study can provide a reference for the design and operation of variable speed pump-turbine.