Study On The Influence Of Blade Placement Angle And Blade Trimming On Turbine Performance Of Volute Axial Flow Pump

As a kind of equipment for recovering and reusing liquid residual pressure energy,pump reversing hydraulic turbine is widely used in process industry with its advantages of low cost,stable operation and simple structure,which has very important economic value and farreaching social significance.At present,the research object of pump reversing as hydraulic turbine is mainly concentrated on centrifugal pump,and centrifugal pump reversing as turbine is only suitable for the occasion of high pressure head.Therefore,in order to effectively recover the residual pressure energy of large flow and low pressure head,it is of great significance to study the reversal of axial flow pump as hydraulic turbine.In this paper,a PLK XII volute axialflow pump with a specific speed of 900 produced by a domestic enterprise is taken as the research object.Based on the geometric parameters of the spiral case axial-flow pump,a threedimensional model is established.The unstructured grid is used to discretize the computational domain,and the SST K-? turbulence model and SIMPLEC coupling algorithm are used to simulate the pump.The external characteristics and internal flow law of pump and hydraulic turbine are studied in depth.The main research results are as follows:1.Changing the blade angle means changing the design condition of axial-flow pump and widening its operation range.Based on the optimal efficiency point,the flow conversion coefficient KQ,head conversion coefficient KH,efficiency conversion coefficient K? and shaft power conversion coefficient Kp of pump and hydraulic turbine under different blade angle were obtained.The results show that when the blade angle is 12°,KQ = 1.31,KH = 1.22,K? = 0.92 and Kp = 1.05;when the blade angle is 14°,KQ = 1.22,KH = 1.68,K? = 0.94 and Kp = 1.12;when the blade angle is 16°,KQ = 1.06,KH = 2.66,K? = 0.97 and Kp = 1.23.2.The axial force is one of the important factors that affect the safe and reliable operation of the pump as a turbine.The strength of the pump shaft obviously meets the design requirements under the pump condition,but the pressure head when the pump is reversed as a turbine is larger.Therefore,the axial force under the turbine condition needs to be calculated to ensure that the pump shaft strength still meets the requirements.The axial force of the cantilever axial flow pump mainly comes from the liquid acting on the blade and hub.According to the calculation,the axial force of turbine is 1.44 times of that of pump when the blade angle is 14 ° and the pump shaft still meets the strength requirements after checking.3.For the pump condition,the inlet edge of the blade has been rounded,but when the pump reverses to be a hydraulic turbine,the pump outlet becomes the inlet of the hydraulic turbine.In order to improve the performance of the hydraulic turbine,the inlet edge of the blade is fillet treated to make the blade inlet edge thin and round,so as to reduce the collision loss of fluid flow at the blade inlet.The airfoil with four cylindrical surfaces a,B,C and I are selected for fillet treatment.Through numerical calculation,the efficiency,head and shaft power are increased by 2.31%,2.55% and 2.83% respectively at the optimal efficiency point of turbine operating conditions.