Mixed-flow Forced Circulation Pump Energy And Internal Flow Characteristics Numerical Calculation And Experimental Analysis

Pumps play an extremely important role in agricultural irrigation,improving agricultural production conditions and achieving high and stable yields.This thesis takes a mixed-flow forced circulation pump as the research object,and uses a combination of theoretical analysis,numerical calculation and experimental research to study the mixed-flow forced circulation pump in forward and reverse operation.The three-dimensional model of the mixed-flow forced circulation pump is established by Solidworks software,and the calculation area is meshed by ANSYS.The internal flow field of the mixed-flow forced circulation pump in forward and reverse operation under different flow conditions is then numerically calculated by CFX software,and the external characteristics and internal flow field distribution patterns of mixed-flow forced circulation pump in forward and reverse operation are analyzed.The model of the mixed-flow forced circulation pump is fabricated by 3D printing technology and a test bench is built to verify the numerical calculation results by the test data obtained.This thesis combines numerical calculations and experiments to obtain the following results:（1）The mixed-flow forced circulation pump forward and reverse operation,both in the design flow condition Q_d=18.78L/s when the highest efficiency,during forward operation,the highest efficiency is 63.64%,head 1.74m.During reverse operation,the highest efficiency is 68.24%,head 2.00m.According to the analysis of the hydraulic performance parameters of the mixed-flow forced circulation pump can be obtained,mixed-flow forced circulation pump reverse operation of the guide lobe outlet velocity uniformity and flow rate weighted average the angle increases with the flow rate,and the uniformity of flow velocity at the outlet of the guide vane can reach up to about 75%,while the highest forward operation can reach about 65%.Reverse operation compared to forward operation guide vane outlet flow velocity weighted average angle change is smaller,the change is more gentle.The hydraulic loss curve of the guide vane section in forward and reverse operation has the same trend and decreases with the increase of flow,and the hydraulic loss of the guide vane section is larger under the small flow condition（0.58Q_d-0.92Q_d）,and smaller under the large flow condition（1.08Q_d-1.5Q_d）.（2）In forward operation,there is a stagnant area at the corner of the vertical section of water inlet,the flow velocity at the upper part of the horizontal section of water inlet is obviously smaller than that at the lower part,and there is a backflow phenomenon and formation of vortex before the inlet of the impeller at the upper part of the horizontal section of water inlet;The pressure distribution in the water inlet section is small,and the pressure distribution in the guide vane section and the water outlet section is large.In reverse operation,vortices are generated in the lower left end of the outlet horizontal section,and the flow line is roughly in the shape of an arc belt contracting to the left of the vertical outlet section and forming larger vortices on the right side of the outlet vertical section.（3）Forward and reverse operation,impeller blade suction surface blade on the low pressure area is mainly distributed in the middle of the blade,high pressure area is distributed in the blade leading edge and trailing edge;At the same time in the middle of the blade pressure gradient is small,and the blade leading edge and trailing edge of the flow separation phenomenon,resulting in more pressure partition.（4）Compared with the forward operation,the impeller inlet velocity vector and the guide vane outlet velocity vector are more evenly distributed in the reverse operation.The impeller inlet velocity vector is roughly distributed in a circular belt with the velocity vector increasing in a gradient from the center to the outer edge,and the velocity vector distributed in the center of the impeller inlet is small and sparse,while the velocity vector near the outer edge of the wheel is larger and denser.In the guide vane exit section there are vortices and the number of vortices is the same as the number of guide vane blades,and there are more gradient and dense velocity vectors distributed in the area between the two blades of the guide vane,and the high speed area is mainly scattered in the middle and outer edge of the guide vane gap.（5）Analysis of the effect of different impeller guide vane number combination matching relationship on the performance can be obtained,the more the number of impeller blades,the greater the head;different impeller guide vane number combination and efficiency of the relationship is relatively more complex.When the efficiency is optimal,the impeller blade number Z₁=3,the guide blade number Z₂=11,the efficiency is69.22%,the head is 1.64m.When the efficiency is lowest,the impeller blade number Z₁=7,the guide blade number Z₂=7,the efficiency is 65.88%,the head is 2.13m.