Analysis Of Pressure Pulsation Under Rotating Stall Of Pump-turbine In Pump Mode

Pum ped-storage plants are widely constructed and used as they consider both energy storage and power generation,which can convert excess electricity into more valuable power.With the integration of renewable energy such as wind energy and solar energy into the electricity grid,the conversion of pumped-storage units is more frequent,which requires the pump-turbine to have better stability of the operating.Rotating stall is one of the important factors affecting the stable operation of rotating machinery.Rotating stall will cause vibration of the unit,which will cause resonance of the unit when serious,and bring great hidden trouble to the safe operation of the unit,therefore,the study of rotating stall characteristics of pump-turbine has extremely high engineering value.The study on the time-frequency characteristic of the pressure pulsation of each part of the pump-turbine under the condition of rotation stall can analyze the mechanism and propagation rule of rotation stall.The author simulate and analyze the flow characteristics and pressure pulsation characteristics,a pump turbine unit in a pumped-storage plants,in the flow field under rotating stall condition by CFD method.The main conclusions are as follows:(1)According to the study,it is found that in the optimal operating flow range of0.2~0.76 times,rotating stall occurs in guide vane;At 0.2 times optimal flow rate,the phenomenon of the rotating stall in the guide vane region is the most intense,and four rotating stall regions are distributed in the guide vane channel;The flow separation in the non-stall channel is aggravated by the flow separation at the outlet of the movable guide vane and the reflux at the outlet of the fixed guide vane,resulting in the rotation stall region rotating circumferential within the fixed guide vane.(2)The pressure pulsation of spiral case decreases first and then increases along the rotation direction,and the fluctuation becomes more obvious as the distance from the tongue is closer,but the increasing trend disappears under the condition of rotating stall;the frequency of pressure pulsation is mainly concentrated in the low frequency region.(3)As the flow rate decreases,the blade vortex is gradually produced and developed from the inlet of the guide vane.When the flow rate decreases to a certain extent,the blade vortex appears in the stay vane and develops in the stay vane with similar laws,the smaller the flow rate,the shorter the evolution period;The vortex in the stall channel hinders the flow through the channel,and the flow diverts into the non-stall channel at the interval between the stay vane and the guide vane,thus,the flow separation in the non-stall channel is intensified,and a high-speed jet appears in the non-stall channel.(4)As the flow rate decreases,the peak value of pressure pulsation in the stay vane increases;The phenomenon of rotating stall under partial load condition inhibits the interference between components,the pressure pulsation of the guide vane is mainly affected by the runner,and the amplitude of the pressure pulsation at the inlet of the movable guide vane increases,but the amplitude of the increase is slightly smaller.(5)Under the condition of rotating stall,the pressure fluctuation of runner runner appears 9 times in one cycle due to the interference of compartment region,and the pressure appears 4 times in the middle of runner due to the effect of stall mass,the change period is related to the number of stall masses;the amplitude of pressure pulsation of runner pressure surface is larger than that of suction surface.