Research On Design Methodology And Experiment Of Special Impeller Using In Turbine Mode Of Centrifugal Pump As Turbine

Due to the advantages of relatively cheap,easy to manufacture and maintain,and small et al,the reverse running pump could be one of the effective ways of pico,micro,and mini hydropower development in remote areas and pressure energy recovery in the industry.With economic and technical considerations,single-stage centrifugal pump-as-turbine(PAT)is recommended by many researchers in the low-capacity range(up to 100 kW)of hydropower development.Single-stage centrifugal pump is mostly equipped with the spiral volute.Because of space size restriction,there are usually no adjustable guide vanes,which leads to fluid directly flowing into impeller inlet from volute outlet when pump operates in turbine mode.Furthermore,the blade inlet/outlet angles and blade shape of original impeller designed for pump working condition,not for turbine mode;do not match well with turbine running condition.Thus the turbine mode of PAT efficiency is universally not high and the high efficiency range is usually narrow when pump reversely operates as turbine directly.And the performance of PAT is usually unknown,which causes accuracy of the PAT's parameter prediction is not high.It is difficult to select the appropriate pump as turbine.Therefore,research on the predictable performance high-efficiency special impeller using in turbine mode of PAT is of great significance to improve the utilization rate of existing pressure and solve the key scientific problems in the development of small power liquid pressure.In this paper,research on design methodology and experiment of special impeller using in turbine mode of centrifugal pump as turbine was performed using theoretical,numerical and experimental analyses.The main work and creative achievements of this paper were:(1)The current research status of PAT both at home and abroad was summarized;meanwhile its future development trends were forecasted.The conversion relationship between the positive and negative performance parameters of the pump was summarized.(2)The influence of the radial clearance distribution,grid number,turbulence model and other key factors in numerical calculations on the external characteristics of PAT was studied.A turbine test rig was set up.A test on the pump as turbine was carried out.A more accurate numerical calculation method of PAT was put forward by comparing the numerical calculations and experimental results.(3)The idea of replacing the prototype pump impeller with the special impeller for turbine to fundamentally improve the PAT efficiency was proposed.The method of calculating the equivalent circle radius of the spiral inlet section of spiral case according to the principle of equal area was first proposed.The relationship between the geometric parameters of the spiral case and the inlet moment of the impeller was derived.The prototype pump impeller and the special impeller for turbine were tested on the same test rig.The comparison test results confirmed that the special impeller for turbine can significantly improve the operation efficiency of the PAT,and the high efficiency area is wide.(4)The influence of the blade inlet angle,blade inlet width and impeller diameter on the high-efficiency point flow of the turbine was analyzed theoretically for the first time,and verified through numerical calculations.The relationship between the derived blade geometric parameters and the designed calculation flow was confirmed.By analyzing the influence of blade inlet angle,blade outlet angle,the change rule of the blade inlet/outlet angle,impeller diameter,blade inlet width and blade number on the hydraulic turbine performance,the determination method of geometric parameters for the special impeller were put forward,to provide a useful reference for design of special impeller.(5)The design methodology of the special impeller for turbine in this paper were applied to the PAT at medium and high specific speed.The special impeller for turbine at the corresponding specific speed was developed.The optimal value range of the blade inlet angle of the special impeller for turbine at different specific speeds was analyzed,and the performance test was performed.The results show that the PAT's efficiency at 66,132 and 193 specific speeds increased by 7.93%,8.07% and 5.45%,respectively,after replacing the prototype pump impeller with the special impeller.The results confirmed that the special impeller for turbine can significantly improve the operation efficiency of the PAT.(6)The theoretical design flow rate and numerical calculation result of turbine high-efficiency points at different specific speeds and different inlet angles were summarized.Through comparisons,it was found that the relative deviation between them is within 5%,indicating that the relational expression between the blade inlet angle and design flow rate derived in this paper can effectively predict the high-efficiency point flow of the special impeller for turbine.A theoretical prediction method for the actual head of the turbine was proposed creatively.(7)The change rule of the external characteristics of different specific-speed turbines at different speeds was studied thought experiment.The results indicated that there are certain deviations between the experimental performance parameters at different speeds and the theoretical calculating value applying the proportional law.The farther away from the rated speed,the greater the speed deviation is.The CFD calculating value was consistent with the theoretical calculating values applying the proportional law,but CFD cannot objectively reflect the effect of variable speed on the efficiency.The influence of variable speed on the turbine efficiency was analyzed.The rule that the deceleration has a negative effect on the volumetric efficiency,and the acceleration has a nonlinear positive effect on the mechanical efficiency in a certain range was clarified.This paper analyzed the characteristics that the farther away from the rated conditions,the more obvious the efficiency drop is,and the more significant the effect of the deceleration operation efficiency improvement is under partial turbine operation.The economic operation scheme under the partial turbine operation was proposed qualitatively,to provide a useful reference for the efficient and economical operation of PAT.