Influence Of Blade Inlet And Outlet Angle On Pump As Turbine And Research On Impeller Cutting Rule

The pump as turbine is used in petrochemical,iron-steel,coal-chemical industry,desalination and many other process industry,which is for the recovery of liquid pressure energy.The pump as turbine is widely used,because of its low price,simple structure,specifications etc.But there are problems such as narrowed high efficiency area,low turbine efficiency and unstable operation.The domestic and foreign scholars mainly concentrated in the pump turbine,force characteristics and performance optimization in three aspects.A large number of research and literature reports is that the efficiency of pump reversing is generally lower than the efficiency of the pump,which is because the design of the pump is mainly designed according to its operating conditions.The inlet angle of the blade is not in accordance with the turbine condition,and the change law of the vane line of the pump does not conform to the working condition of the pump for the turbine.Besides,volute and other overflowing parts also have important influence on the performance of hydraulic turbine.In the pump,with the increase of specific speed,the pitch angle of the tongue also becomes larger.The recommended range of the pitch angle of the tongue in specific speed of 40~60 with spiral case is 0 ~15 degrees.Under the condition of the turbine,the repose angle of the tongue is not necessarily consistent.The study of the effect of the angle of the tongue on the performance of the turbine has not been reported.Under turbine condition,the angle of tongue separation is not always consistent.The research on the influence of tongue placement angle on turbine performance has not been reported.In order to increase the range of reversing of the centrifugal pump,and the cutting of the turbine impeller may increase the working range of the pump,it is necessary to study the effect of the impeller cutting on the turbine performance.The main work done in this article is as follows:1.Based on Turbine Theory,a design method of inlet and outlet angle of hydraulic turbine impeller is used.A single stage single suction centrifugal pump with a specific speed of 48 is used as the research object.According to the proposed method,the inlet and outlet angles of the impeller blades are calculated under the two conditions of the front and back bending of the turbine blade.In the case of front and back bending of the blade,the blade profile is designed in three forms,"convex","straight line" and "concave".The maximum thickness of the blade is calculated according to the strength.The blade thickening rule is thickened according to the low speed airfoil of NACA.The whole model of turbine impeller is simulated by ANASYS Fluent software.It is found that the hydraulic efficiency of the hydraulic turbine impeller model,which is designed according to the turbine theory,is about 80%,and the hydraulic efficiency is higher than that of the direct reverse turbine.The hydraulic efficiency of the back bending blade turbine is better than that of the front bending blade.The front bending blade with the profile line is concave makes the efficiency curve flat and the efficiency area wide.2.In order to study the influence of tongue placement angle of the volute on the hydraulic turbine,the hydraulic turbine impeller was selected with the front bending blade and the profile line is concave which was designed in the previous article with the specific speed of 48.On the basis of the prototype pump of 10 degrees tongue placement angle of the volute,19 degrees and 28 degrees were added to the volute to make the three different volutes.With the numerical simulation of fluid analysis software ANSYS CFX,the results show that hydraulic efficiency of the hydraulic turbine model with 19 degree tongue placement angle is the highest,which is 0.73% higher than that of the prototype volute hydraulic turbine,and the efficiency curve becomes very flat,and the high efficiency area is greatly increased.3.In order to study the performance changes of the reverse pump after cutting the turbine impeller,the law of cutting the impeller is derived to adapt to the low,medium,high specific speed.A single stage single suction centrifugal pump with a specific speed of 40 and 113 is reversed as a hydraulic turbine,and the impeller is cut three times(3%,6%,9%)without changing other over current components.The hydraulic turbine before and after impeller cutting is numerically simulated by ANSYS CFX software,and compared with the cutting formula.And compared with the cutting formula,it is found that when the cutting quantity is less than 3%,the error of flow,pressure head,shaft power and numerical simulation results calculated by cutting formula is small.With the increase of cutting quantity,the error increases.It can be seen that the formula of turbine impeller cutting can predict the turbine performance when the cutting volume is small.