Study On The Characteristics Of S-Shaped Zone In Pump Turbine

In the rapid development of the economy today,both industrial and residential electricity demand is increasing,at different times the huge difference in user electricity requirements of the grid to expand the scale at the same time with greater and more flexible ability to adjust.The pumped storage power station with the function of peak load shaving is an effective means to realize this goal.However,due to the existence of an unstable "S" characteristic zone in the full characteristic curve of the pump turbine,it is often caused by the difficulties of the start-up of the unit and the instability of the no-load,resulting in huge economic losses.In order to solve the serious impact of this unstable area,it is necessary to take the method to study the characteristics of "S" zone.Based on the computational fluid dynamics method,this paper studies the flow state and pressure pulsation of the pump turbine under steady and unsteady conditions,and solves the problem of "S" shape.The main research contents are as follows:1 Making a steady calculation of pump turbine on turbine mode,runaway speed operating condition and braking condition.The influence of the opening degree of different guide vanes on the flow field in the guide vane area and the runner area was analyzed.At the same time,the load of the runner blades under different working conditions was analyzed.Under turbine condition,the blade is subjected to the positive moment.Under runaway condition,the head and tail of the blade are subjected to the negative moment,and the middle part of the blade is subjected to the positive moment.Under the braking condition,the blade head and tail are negative Moment,the middle of the blade is subjected to a torque of 0.2 The unsteady numerical calculation of the pump turbine in turbine condition,runaway condition and braking condition is carried out.The flow characteristics of the flow field in each overcurrent component are analyzed,the energy characteristics of the pump turbine under the conditions of the turbine,the running conditions and the braking conditions,and the variation of the pressure pulsation of each overcurrent component.The results show that the vaneless space and the runner area are in the same direction as the runner rotation in the runaway condition,and the rotation speed is 0.5 times and 0.6 times the speed of the runner.Under runaway condition and braking condition.The runner is formed in the same direction as the direction of rotation of the runner along the pipe wall and the rotational speed is 0.55 and 0.85 times the rotational speed of the runner.The design conditions(turbine conditions)and off-design conditions(runaway conditions and braking conditions)in the energy characteristics of the main difference in guide vane region;pressure pulsation analysis shows that the pressure pulsation in the volute and the trachea is low-frequency pressure pulsation,the guide vane pressure fluctuation is affected by rotor-stator interactions.The analysis of the axial force of the runner shows that the axial thrust of water under runaway condition will oscillate with high frequency,and the axial force under braking condition tends to lift the whole turbine.