Research On The Influence Of The Arrangement Of The Modified Guide Vanes On The "S" Characteristic Of The Pump-turbin

Hydropower and thermal power,as the main ways of power generation in China,have made indelible contributions to China’s power industry.In order to meet the efficient operation of power grid,pumped storage power station has become the mainstream means of energy storage and power grid regulation.As the core energy conversion component of pumped storage power station,pump turbine has the function of pump and turbine at the same time.During the peak period of power consumption,the gravity potential energy of the water source stored in the upstream reservoir is used for power generation and grid connection.During the low period of power consumption,the surplus electric energy in the power grid is used to lift the water in the downstream reservoir to the upstream reservoir and convert the electric energy into the gravity potential energy of water for storage.As an energy conversion component,pump turbine has high standards of efficiency,stability and safety.However,when pump turbine operates in"s"zone,it will bring many instability problems.For the improvement of"s"characteristics,the research results of this subject are as follows.The optimized guide vane is replaced with the original guide mechanism in different layout,the different schemes are modeled and meshed,and the three-dimensional numerical calculation of the whole channel is carried out.The evolution mechanism of the internal flow field in the vaneless area behind the runner and behind the guide vane under different schemes is discussed,and the influence of different schemes on the"s"characteristics is analyzed.The results show that the replacement of the optimized guide vane into the original guide mechanism has different degrees of influence on the"s"characteristics of the unit,but this influence is and the influence contains both positive and negative aspects.Finally,an optimal scheme is selected through the flow field analysis,the n₁₁-Q₁₁curve and the pressure pulsation analysis of the non-blade area in front of the runner behind the guide vane.The numerical calculation of the starting process of the pump turbine equipped with the original guide vane is carried out.Through the analysis,it is found that the vortex flow in the channel has inheritance,and the vortex structure in the channel has a great influence on the blade load.The steady-state and unsteady state calculations of the optimal scheme under specific working conditions are carried out,and the vortex core structure in the flow field is analyzed.It is found that the vortex flow in the whole channel starts at the junction of the volute and the fixed guide vane.Due to the impact of the incoming flow on the structure and the hysteresis effect,the vortex flow will always appear downstream and continue in different ways until the rear of the draft tube.The three-dimensional unsteady state calculation of the pump turbine equipped with the optimal scheme guide mechanism is carried out.The pressure,streamline,turbulent kinetic energy,pressure pulsation in the vaneless area in front of the runner and the runner behind the guide vane,and the pressure,streamline and turbulent kinetic energy in the draft tube area are analyzed.The results show that the optimal layout scheme of guide vanes in the original water guide mechanism can effectively break the high-speed water ring in the vaneless area,greatly increase the inflow in the runner area,and improve the flow pattern in the runner area.Through the analysis of the pressure nephogram of the runner and movable guide vane area,it is found that the high-pressure area is mainly concentrated at the head of the movable guide vane,which is mainly because when the opening angle of the guide vane is certain,the movable guide vane area cannot meet the nonimpact inflow,and there is stagnation at the head of the guide vane,resulting in the increase of the pressure in this area.Through the analysis of the turbulent kinetic energy nephogram in the runner and movable guide vane area,it is found that there is a certain degree of energy dissipation in this area,which is mainly due to the fact that the incoming flow can not meet the non impact inflow,normal outflow and the interference between the moving and stationary cascades.From the frequency domain diagram of pressure pulsation in the vaneless area,it can be found that the pressure pulsation in the vaneless area fluctuates in a certain period and will gradually stabilize in the area with the passage of time,and the relative amplitude of the pressure pulsation at the detection point where the four monitoring points are away from the diaphragm in a clockwise direction is the smallest.Through the analysis of the draft tube area,it is found that the flow pattern in the draft tube area changes greatly with the change of flow,the pressure always presents the form of low pressure in the middle,high pressure on both sides,low pressure at the inlet and high pressure at the outlet,and the energy dissipation mainly appears in the central area of the straight cone section and the inner side of the elbow section,This is mainly caused by the influence of vortex flow in the runner area and the impact of incoming flow on the structure.Overall,after the optimization design of the movable guide vane airfoil,the"s"characteristics of the pump turbine are effectively improved under the condition of only a small decrease in efficiency,and the pressure pulsation in the vaneless area shows an improvement trend.