Flow Characteristics Analysis of a High-Head Prototype Pump-Turbine During Turbine Start-Up: Effects of the Clearance

Abstract

The dramatic changes in the internal flow and the corresponding structural behavior during the turbine start-up transient process of pump-turbines are extremely complex. The clearances in the upper crown chamber and bottom ring chamber affect the results of the flow field and structural field of the pump-turbine runner. Most of the previous studies ignored the effects of the clearance flow field to simplify the numerical simulations. In this study, numerical calculations were performed on the entire flow passage of a high-head prototype pump-turbine during the start-up in turbine mode, and the model with and without the clearance are analysed respectively. The causes of the flow field characteristic difference and external characteristic difference caused by the existence of intermediate clearance in the model are studied in detail. The results show that the clearance flow field has a great influence on the axial forces on the runner, which is mainly due to the higher pressure of the clearance flow field compared with the flow field in the runner; At the same time, because the existence of clearance flow field only has a small effect on the distribution of internal flow field, the hydraulic torque of runner considering clearance effects is basically the same as the one without clearance.