Research On The Effect Of Tip Clearance And Guide Vanes On The Performance Of Axial Pump As Turbine

For the rural,remote and mountainous areas of developing countries,it is still unable to connect to the power grid,because the construction of small/Micro Hydropower and the use of conventional turbines face huge investment costs.As a kind of reversible hydraulic machinery,pump as turbine(PAT)in reverse operation can generate electricity.At the same time,it has the advantages of simple structure,easy installation and low price,which can solve the problem of high cost of small/micro hydropower system.Therefore,it is of great significance to establish an isolated power grid by using small/micro hydropower system,such as using axial-flow pump reverse to generate electricity.This article takes the axial flow pump with a specific speed of1075 reversed as a hydraulic turbine as the research object.The main research contents are as follows:1.Effect of tip clearance on performance of axial flow pump as turbineIn order to study the effect of tip clearance on the performance of axial flow pump as turbine,referring to the existing literature on tip clearance of axial flow pump,five tip clearances of 0.6mm,1.0mm,1.5mm,2.0mm and 2.5mm were selected to calculate the constant value of hydraulic turbine under the reverse turbine condition.The results show that the tip clearance has little influence on the head and power of the axial flow pump as turbine under the condition of small flow rate,but it has obvious influence on the head and power under the condition of large flow rate,and the head and power gradually decrease with the increase of the clearance.When the clearance value increases from 0.6mm to 2.5mm,the efficiency of the hydraulic turbine gradually decreases by 1.93%,and there is little difference between the efficiency of each clearance under high flow condition.2.Research on pressure fluctuation characteristics of axial flow pump as turbineThrough the unsteady numerical simulation of the flow field in the axial flow pump reverse turbine,the distribution law of the pressure pulsation in the axial flow pump as turbine and the influence of different clearance on the pressure pulsation in the turbine are analyzed.The results show that the main frequency of the pressure pulsation in the axial flow pump reverse turbine is equal to the frequency of the guide vane,and the pressure pulsation in the impeller is guided The closer to the guide vane,the stronger the interference.The main frequency of pressure fluctuation at the interface of guide vane,outlet section and flow passage parts is equal to that of blade,and the pressure fluctuation is related to the number of blades.The results show that the tip clearance does not change the periodic characteristics of the pressure fluctuation at the monitoring points near the impeller wall,but affects the amplitude of the main frequency of the pressure fluctuation.With the increase of the tip clearance from0.6 mm to 2.5 mm,the amplitude of the main frequency of the pressure fluctuation at the monitoring points near the impeller wall decreases gradually.3.The influence of with or without guide vanes on the performance of the axial flow pump as turbineIn order to analyze the influence of the guide vanes on the performance of the axial flow pump as turbine,the steady numerical simulation of the axial flow pump is carried out under the condition of the guide vane and the no guide vane.The results show that the power of the hydraulic turbine head and the shaft is obviously greater than that without the guide vane,and the difference between the pressure head and the axial power between the vanes and the guide vanes increases with the increase of the flow rate.The efficiency difference between guide vane and guide vane decreases with the increase of flow rate,13% higher efficiency with and without guide vane under small flow condition,9.37% higher efficiency under optimal condition than that without guide vane,and no guide vane under high flow condition.