Numerical investigation on transient flow of a high head pump-turbine in pump mode during rapid closure of guide vanes

Abstract

Transient flow in pump turbines appears because the hydropower storage plant needs to experience variable operation modes to make a balance between the electricity production and consumption, thus causing high-pressure fluctuations and shortening life expectancy. In this paper, three-dimensional numerical simulation, based on Detached Eddy Simulation (DES) turbulent model, was carried out to investigate the flow characteristics in a high head pump turbine in pump mode during rapid closure of wicket gates. The dynamic mesh technique was applied to simulate the rotation of the guide vane. In this work, the influence of water compressibility on pressure fluctuations was considered. The transient flow characteristics during load reduction were investigated by time-frequency analysis methods of the numerical data. KEYWORDS IntroductionLast decades have witnessed an increasing consumption of renewable energy due to the increasing price of fossil fuels and damage of carbon dioxide emissions on the living environment. The development of wind energy, solar power energy, hydropower energy and clean energy has been put into investigation for many years. However, it is a challenging task to control the stability of the output of renewable energy transmitted to the electricity grid because of stochastic nature of the renewable energy and fluctuating requirement of customers.In the renewable energy system, hydropower pump storage plant has been deemed as a costeffective electricity storage technology to balance the output of renewable electricity and need of the customers. Even though hydropower pump storage plants has such advantage, it needs change the operation modes between the pump mode and turbine mode frequently to meet the unpredictable need of electricity consumption, leading to transient instable flow in the pump-turbine under variable transient processes including the start-up, stop and adjusting rotating speed and so on. Besides, one of the common transient processes is that the wicket gates are required to open or close frequently. The transient instable flow including the flow separation, back flow and rotating stalls can cause severe pressure fluctuations, resulting in the vibrations of pump-turbine, even reducing the operating life expectancy and accidents. Thus, it is very important and urgent to investigate the transient flow mechanism for reducing the unstable flow [1].Many numerical and experimental investigations on the unsteady flow that are rotor-stator interaction and rotating stall have been carried out on pump-turbine at pump mode and turbine mode at the constant flow rate [2][3][4][5][6][7]. In terms of research on the transient process, the transient processes that are runaway, no-load, load rejection and so on are studied in pump turbine at turbine mode by numerical simulation and experimental methods. Cavazzini et al [8] simulated the transient flow in pump turbine at turbine mode under no-load condition. She pointed out that the head began to increase due to the fully developed rotating...

Research on the Internal Flow Difference between Peak and Valley Conditions of Water Jet Propulsion Pump during Working at Hump Region

“…This leads to the formation of a valley point on the flow-head curve, ultimately resulting in the hump phenomenon. Yang Jun, G. Pavesi, Uroš Ješe, O. Braun, and others [17][18][19][20][21] attributed the hump phenomenon in pumpturbines under pump operation to the influence of the dynamic-stator interaction on the flow structure and pressure pulsation inside the runner outlet and adjustable guide vanes.…”