Numerical Study And Analysis Of Inner Flow In Reversible Pump-turbine

Pumped storage power plant displays the effect of peak cutting and valley filling in the grid.The capacity of pumped storage power plant has continuously extended in recent years.Pump turbine as the main equipment of the plant frequently transforms among different operations to satisfy the requirement of grid,and inevitably runs in the unstable conditions.When pump turbine is operated at the runaway and turbine braking mode which in the unstable zone of S characteristic,many serious stability problems will occur,such as the strong pressure fluctuation,large shaft swing,abnormal noise and fatigue fracture of unit components.It is difficult to observe the complex flow in pump turbine and get the detail date on site.Therefore,a simulation method based on the model unit was adopted to research the hydraulic mechanism of these instable phenomena.The larger openings with 24°,21°and the smaller opening with 6°and five working conditions(turbine,runaway,turbine braking,zero discharge and reverse pump)were selected to analyze the inner flow of pump turbine.The calculation is implemented by the combination of commercial software and analysis program of complex flow structure developed by myself.A mathematical model of vortex identification method is established.The typical vortex structure in the different regions of the pump turbine is identified by appropriate approaches.The effect of working conditions of pump turbine on the form of vortices is also studied.The discharge intensity and occur position of the backflow in the pump turbine are quantized.The hydraulic force on the impeller is calculated and analyzed.The main research efforts can be summarized as follows:(1)The rotating invariant method programmed by myself identifies more vortices in the impeller and vanelesss of reversible pump turbine.Some vortices have a high vorticity.(2)The form of vortices has a big difference among different guide vane openings.When the discharge is low,the obvious vortices generated in the flow passages with the deterioration of inner flow.(3)The backflow often occurs at the turbine braking and runaway working conditions,presenting an obvious spatial distribution,but they rare occur in turbine working condition.(4)The main force on the impeller is hydraulic force which can be decomposed into two forces: one in parallel with the shaft and the other in perpendicular to the shaft.These forces are influenced by the working conditions.The generation of these forces is related to the flow phenomena.