Numerical Simulation And Experimental Research On Impeller Of Mixed-Flow Pump As Turbine

Liquid pressure energy is a clean and renewable energy source.Pump as turbine is a kind of low power liquid pressure energy development and energy-saving equipment.Compared with micro turbines,it has the advantages of small size,simple structure,low cost,and convenient maintenance.It has a wide range of applications in small hydropower stations and industrial processes.At present,there are few equipments for the utilization of liquid pressure energy with large flow rate,low and medium-head.However,it is difficult to select the mixed flow pump as turbine which is suitable for large flow rate,low and medium head pressure energy.So it is necessary to study the turbine design method of the mixed flow pump as turbine.Impeller is the core component in the energy conversion process of mixed flow pump as turbine.It is siginificant to do research on impeller,study the optimization design method of turbine impeller,and improve the utilization of low power liquid pressure energy.It can promote the development of rural hydropower and the construction of clean and low carbon,safe and efficient energy system.This paper adopts the method of experimental,numerical simulation and theoretical analysis to study the internal flow,impeller trimming and optimal design of turbine impeller parameters.The main work and creative achievements of this dissertation were:(1)Two mixed flow pump as turbines with specific speed of 222 and 264 are designed and manufactured.The test rig is built to test the performance of the mixed flow pump as turbine.The CFD software was used to simulate the performance of the turbine.The effects of grid number and turbulence model on the external characteristics of the mixed-flow pump in the numerical calculation process are studied and an accurate numerical simulation scheme for mixed flow pump as turbine was obtained.(2)The internal flow in mixed flow pump as turbine was studied.The flow distribution and hydraulic loss distribution in different components of mixed flow pump as turbine are studied.The flow patterns in turbine are summarized and thereasons for the drop of turbine's efficiency were analysed.It can provide theories basis for the improvement of the turbine's efficiency.(3)The impeller trimming of mixed flow pump as turbine were innovatively studied.The turbine performance were obtained by the experiments.It is found that the error of best efficiency point between the result of experiment and theoretic calculation of mixed flow pump is smaller than 4.17% and the error of head is smaller than 4.8%.So it has certain accuracy to apply the impeller trimming law of mixed flow pump to predict the performance in turbine mode.The flow change and hydraulic loss change in turbine was analysed and the reasons for the change of efficiency were concluded.The influence of cover trimming was studied and it is found that the covers should be retained when the impeller trimming is carried out.(4)The impeller of mixed flow pump as turbine was redesigned.The influences of the change of inlet angle,outlet angle,inlet width,blade number and blade wrap angle of the impeller on the performance of mixed flow pump as turbine were studied and the high efficiency design theory was verified by experiment.The high efficiency design theory is used to design the mixed flow pump as turbine whose head is 10 m and shaft power is 5 kW.The product has been successfully applied in turbine market.