Optimization of surge tank structures in hydropower station based on VOF method

Abstract

During transient processes of hydropower stations, large surging waves under load rejection condition and air-trapped vertical vortices under start-up condition in surge tanks are the critical factors that influence the safety of hydropower stations. In this study, model tests and volume of fluid (VOF) model based three-dimensional (3D) simulations were conducted to check the rationality of surge tank structures in transient processes, and after intensive analysis, an optimized scheme was proposed. The results show that the original scheme leads to the violent water level fluctuations in steady operation and load rejection conditions, and some air-trapped vertical vortices occur during start-up process. The air-trapped vertical vortices can provide bubbles into the penstock, which is not permitted. With the impedance orifice and bottom plate shapes changed, the optimized scheme gives limited water level fluctuations during both load rejection and start-up conditions, and eliminates the step water falling and air-trapped vortex swirling phenomena effectively, meeting the requirements of design, construction and operation.