Study On Hydraulic Optimization Of Multistage Centrifugal Pump As Hydraulic Turbine Guide Vane

In today ’s increasingly tense energy,it is particularly critical to promote a green,energy-saving and efficient industrial structure.As a commonly used hydraulic machinery,the reverse pump can be used as a hydraulic turbine(Pump as Turbine,PAT)to recover the pressure energy of the engineering residual liquid.At the same time,it also has the advantages of simple structure,convenient maintenance and low cost,so it has a good application prospect in energy saving and efficiency increasing.However,at present,the problem of low hydraulic performance of pump as hydraulic turbine still exists,especially the efficiency index of multi-stage centrifugal pump as hydraulic turbine which mainly recovers high-pressure liquid energy is not ideal.Based on this,this paper takes an industrial three-stage centrifugal pump as the research object.The main research contents and conclusions are as follows:1.Influence of inlet and outlet angle of positive guide vane on hydraulic performance of multistage hydraulic turbine.Through the analysis of velocity moment theory,three new schemes of inlet and outlet angle combination are proposed,and then the flow field simulation and comparative analysis are carried out with the initial scheme.The results show that the design without incidence angle at the inlet of the positive guide vane is beneficial to the turbine operation under the pump condition,and the incidence angle can be appropriately added at the inlet of the positive guide vane(corresponding to the outlet of the pump condition)to improve the hydraulic smoothness of the blade profile.In the new design scheme C,the outlet angle of the positive guide vane is 7°(without incidence angle)and the inlet angle is 20°(with 2° incidence angle),and the internal and external characteristics are the best.Taking the optimal flow condition as an example,the efficiency of scheme C is 2.15% higher than that of the initial scheme A,and the pressure,velocity,streamline and turbulent kinetic energy distribution of the internal flow field are obviously improved,and the hydraulic loss of impellers at all levels is also reduced.2.Influence of geometric parameters of anti-guide vane on hydraulic performance of multistage hydraulic turbine.Based on the scheme C model,the outlet diameter,blade number,inlet diameter and inlet angle of the reverse guide vane are studied.The results show that the design of too long or too short outlet diameter is not conducive to the smooth diversion of the transition section,and the design of slightly lower outlet diameter than the transition section can better improve the flow here,indicating that the design of the inlet diameter of the reverse guide vane under the pump condition is still suitable for the high efficiency operation of the turbine condition.For the number of reverse guide vane blades,if the number is too small,the bound liquid flow capacity will be greatly reduced,and the vortex will be induced.However,if the number is too large,the crowding out effect on the liquid flow will be strengthened,and there will be more friction loss,which is also not conducive to the stable diversion of the reverse guide vane.In the given 4,5,6,7,8 blades,the initial 6 blade design has better hydraulic performance,indicating that for the multi-stage centrifugal pump with a specific speed of 68,the design of the number of reverse guide vane blades under pump conditions can still operate under turbine conditions with better hydraulic performance.For the study of the inlet diameter of the reverse guide vane,if the diameter is too small,the inlet end is greatly affected by the liquid flow impact and the dynamic and static interference,which leads to the deterioration of the inflow condition of the reverse guide vane.However,if the diameter is too large,the length of the reverse guide vane channel will be shortened,which reduces the internal conductivity,and ultimately leads to the flow separation phenomenon at the trailing edge of the blade.In the given scheme,the inlet diameter of the reverse guide vane is slightly higher than the outlet diameter of the impeller,which is more conducive to turbine operation.Finally,the study of the inlet angle of the reverse guide vane shows that properly increasing the inlet angle of the reverse guide vane can better match the change of the flow angle caused by the increase of the flow rate.In the given angle design,the efficiency is excellent when the inlet angle is 80°.3.The orthogonal test method is used to optimize the multi-geometric parameters of the reverse guide vane.On the basis of the single factor study of the reverse guide vane,the orthogonal test method is used to optimize the design of the reverse guide vane.The optimization factors of this test are the outlet diameter,inlet diameter and inlet angle of the reverse guide vane.Each factor corresponds to three levels.According to the orthogonal table,nine groups of test schemes are selected for numerical simulation,and the efficiency performance of the previous scheme is compared and the results are analyzed.The results show that different anti-guide vane parameters have different effects on turbine efficiency,from high to low: outlet diameter,inlet angle,inlet diameter;according to the range analysis,the final optimization model(scheme E)is obtained,that is,the outlet diameter of the reverse guide vane is 252 mm,the inlet diameter is 126 mm,and the inlet angle is 80°.After optimization,the efficiency is improved in the whole flow range,which is 0.61% higher than that of scheme C and 4.33% higher than that of initial scheme A.In terms of internal flow,the pressure,turbulent kinetic energy and streamline distribution in the reverse guide vane are improved to some extent.