Research On The Influence Of The Number Of Blades And The Volute Shape On The Pump As Turbine And Its Transition Process

The centrifugal pump in reversal is used as hydraulic turbine,because the centrifugal pump only considered the performance during forward rotation in the initial design,the performance of the reversal rotation is not considered,so that when it is reversed as hydraulic turbine,there are problems such as low recovery efficiency and poor stability.Therefore,this article takes IS80-50-315 centrifugal pump as turbine as the research object,and research on the turbine flow characteristics of different blades and volute shape,which is important for its efficient optimization design.In addition,the pump as turbine mainly work under optimal conditions,but it often deviates from the optimal conditions and transitions to small or large flow conditions in actual operation.In the transition process,the coordinated working state of the whole turbine unit is destroyed,which may have an adverse impact on the unit and the system.Therefore,it is of great significance to study the transient characteristics of pump as turbine in the transition process of variable flow,so as to make the turbine unit operate safely and reliably.The main work content and conclusions of the thesis are as follows:1.Through numerical simulation of 6 pumps as turbines with different blade numbers,it is found that the hydraulic efficiency of Z9 is the largest,which is 3.6% larger than that of Z5 under optimal conditions,and the high-speed area in the flow channel of Z9 is larger than other impellers.The pressure pulsation is not only related to the dynamic and static interference between the impeller and volute,but also affected by the volute tongue.The more the number of blades,the smaller the pressure pulsation of the pump as turbine.Both the radial force and the axial force gradually increase with the increase of flow rate.The more the number of blades,the smaller the radial force,and the smaller the fluctuation range with time,the smaller the pulsation amplitude at the main frequency,the radial force difference between Z9 and Z10 is within 5%.In all working conditions,the axial force of Z8 is the smallest,and the difference between Z9 and Z8 is very small.Considering comprehensively,the hydraulic performance of Z9 is the best when the IS 80-50-315 pump as turbine to operate under stable conditions.There is an optimal number of blades for pumps as turbines with different parameters,and the optimal number of blades for low specific speed pump as turbine is more than the number of design blades for the pump.2.Numerical simulation is performed by matching the annular volute and spiral volute with the same impeller respectively.It is found that the optimal working conditions of the two pumps as turbines are the same.The efficiency of the spiral volute pump as turbine is higher than that of the annular volute pump as turbine.Since there is backflow in the annular volute,the velocity distribution in the width direction of the annular volute is not uniform compared to the spiral volute,and the high-speed area of the annular volute pump as turbine impeller flow channel is smaller than that of the spiral volute.The turbulent kinetic energy of the annular volute pump as turbine is greater than that of the spiral volute,that is,the annular volute pump as turbine has a larger hydraulic loss.The radial force and the axial force of the annular volute pump as turbine are both greater than that of the spiral volute pump as turbine.However,the pressure pulsation in the annular volute is smaller than the spiral volute,and the amplitude of the pressure pulsation on the annular volute tends to be more stable with the increase of frequency than the spiral volute3.In the transient process of variable flow,the use of different transition functions has a significant impact on the transient characteristics of the pump as turbine.By comparing the transient hydraulic characteristics,pressure pulsation and radial force characteristics of the different transition functions,it is found that in the transition process to large flow rate,the use of quadratic function type is the best,and in the transition process to small flow rate,the use of exponential function type I is the best.The fluctuation range of transient hydraulic efficiency decreases with the increase of blade number in transition to large flow rate and small flow rate,at the main frequency,the fluctuation amplitude of hydraulic efficiency of Z7 is the largest and that of Z10 is the smallest,and the difference between Z7 and Z9 is 6.45% and 4.46%respectively.As the increase of the number of blades,the pressure pulsation in the transition process gradually decreases,but the pressure pulsation is larger at the Z10 volute tongue.In the transition process to large flow rate,the peak value of radial resultant force decreases gradually with the increase of blade number,the trough value changes little,and the fluctuation range of radial resultant force gradually narrows.In the transition process to small flow rate,the trough value of radial resultant force gradually increases with the increase of blade number,the peak value changes little,and the fluctuation range of radial resultant force gradually narrows,that is,the radial force resultant force is smaller in Z9 and Z10.Comprehensive consideration,for the IS 80-50-315 pump as turbine in the variable flow transition process,the hydraulic performance of Z9 is also the best.