Numerical Analysis And Optimization Of Internal Flow In Double Suction Centrifugal Pump Under Elbow Inflow Condition

Double-suction centrifugal pump use widely in farmland irrigation,factories,mines,urban water supply and drainage because of its advantages such as large flow,high head,small cavitation allowance and balanced axial force,we usually design the impeller on the basis of uniform inflow.However,in engineering practice,due to space constraints and other factors,we often use the elbow pipe at the inlet of the centrifugal pump,resulting in non-uniform inflow of water pump impeller,thus reducing the pump head and efficiency and threatening the operation stability of the pump.Therefore,it is of great theoretical and practical significance to study the influence of elbow inlet on the internal flow and pressure pulsation of double-suction centrifugal pump,analyze its influence mechanism and explore the improvement method of elbow inflow.In this paper,we took a double-suction centrifugal pump with a semi-helical suction chamber as the research object.For different inlet pipelines,we used UG software to establish a double-suction centrifugal pump model with straight pipe and different elbow pipe inlet,and carried out a numerical study on the internal flow and pressure pulsation of the centrifugal pump by using CFX software.Firstly,we analyzed the internal flow of each passing flow component under different flow conditions.we found that the internal flow field of each flow component is symmetrical,and the change of flow rate affect the energy loss in the suction chamber least,which is manifested as the flow line disorder near the tongue.The change of flow rate affect the energy loss of the volute most.Secondly,we analyzed the external characteristics,internal flow and pressure pulsation of the double-suction centrifugal pump under the inflow condition of different Angle elbow pipe.The results show that the difference in velocity variation law from the same centerline length section at the inlet of the suction chamber leads to secondary flow in the diameter section of large Angle bent pipe and back flow of bent pipe,which reduces the head and efficiency of the pump.The pressure pulsation inside the suction chamber of the elbow increases,while the pressure pulsation outside decreases,but the characteristic frequency of each measuring point remains the same.We use velocity distortion and average deflection Angle to evaluate the evenness of pump inflow.With the increase of bend Angle,velocity distortion decreases and average deflection Angle increases.In addition,on the basis of the above research,we carried out the research on the improvement method of elbow inflow,proposed a method of installing diversion grating to improve inlet distortion.The results show that the diversion gate can change the flow field in the bend pipe,weaken the secondary flow in the pipe,and thus improve the inflow distortion caused by the bend pipe,the effect is related to the position and character of the gate.We selected a reasonable guide grid for the model pump,which effectively reduced the velocity distortion at the inlet of the suction chamber,improved the uneven inflow on both sides of the double-suction impeller,and improved the safety and stability of the whole pump system to a certain extent.