Inter-stage Difference Study On Performance And Pressure Fluctuation Of Multi-stage Deep Well Pump

As the main equipment for extracting deep well underground water and underground oil,deep well pump has been widely used in various fields of industrial production.It is difficult to repair the deep well pump adopting the step-by-step stacking structure,which is in a deep well working environment for a long time,thus improving the hydraulic performance of the deep well pump and reducing the instability during its operation has become a core issue in the field of deep well pump research.Supported by the National Natural Science Foundation of China and the Jiangsu Provincial Natural Science Foundation Project,using ANSYS CFX 18.0 commercial software,steady numerical simulation and unsteady numerical simulation of 250QJ80 deep-well pump model were performed in single-stage,two-stage,and three-level models.The accuracy of numerical simulation was verified by external characteristics test and pressure pulsation test.The main research contents and research results are as follows:(1)The development history of deep well pump products was reviewed,the application of CFD technology in deep well pumps was discussed,and the research status of pump internal pressure pulsation was introduced.(2)Three-dimensional modeling and meshing of 250QJ80 deep well pump were carried out,the grid independence was analyzed,the suitable turbulence model was selected,the appropriate boundary conditions was determined,and the numerical simulation and performance test of the third-stage deep well pump were carried out.It is found that the test results and the numerical prediction results have the same changing rules under the full flow conditions,which proves that the selected calculation method can accurately predict the performance of the deep well pump.(3)Using ANSYS CFX 18.0 software,the performance of the 250QJ80 deep-well pump at the single-stage,two-stage,and three-stage were predicted,and the internal flow field analysis and performance tests were carried out.It is found that the change in the stages of the deep well pump do not affect the performance of a specific series,the head and efficiency of the first stage of the two-stage and three-stage deep well pump are higher than the subsequent stages,and the differences in the head and efficiency of the subsequent stages are little.The main reason for the differences in performance at all stages is that the first-stage impeller inlet media has no pre-rotation,but inlet media of the subsequent stages are all pre-rotating.(4)Based on the study of the transient distribution of the flow field in deep well pumps,the mechanism of pressure pulsation was introduced.Based on the unsteady calculation,the instantaneous characteristics of the pressure in each sub-domain of multi-stage deep well pump were predicted and analyzed.By arranging the monitoring points at the same position(different axial positions)in the impellers,chambers and diffusers at all levels,the pressure variation at different positions in the sub-domains of the deep well pump was obtained.Using the dimensionless pressure and Fast Fourier Transform to eliminate the influence of the pressure magnitude of the monitoring point,the time distribution and frequency distribution of pressure fluctuation signal in the sub-domains at various stages were obtained,and the inter-grade differences of the pulsation signal were analyzed.Finally,the high-frequency pressure sensor was used to complete the instantaneous measurement of the static pressure data in the pump chambers at all levels,and the comparison between the test results and the prediction results was completed.(5)The pressure fluctuation signal has obvious inter-stage propagation phenomenon,and when the direction of the pulse signal propagation is opposite to the flow velocity,the attenuation strength of the pulse signal is greater.The pulsation signals generated by the pulsation sources(the dynamic and static interference)at each stage will have complex coupling phenomena with each other in the deep well pump channel.At the same time,the solid wall surface in the flow field causes the pulsation signal to have the characteristics of instability such as reflection and standing wave.The dither signal is easily attenuated when it propagates in the pump channel,so its propagation distance is very short.In the deep well pump channel,the pressure pulsation propagated between stages is basically the low-frequency signal whose frequency is less than or equal to the main frequency.The low-frequency pulsation signal is prone to propagate in the deep well pump flow path,which in turn causes a gradual superposition of the low-frequency pulsation strength,in which the intensity of the pulsation signal in the first-stage flow path is the most different from the subsequent stages.Under different flow conditions,the components of the low-frequency signal have certain differences,because the propagation and attenuation of the low-frequency signal in the flow field is related to the flow velocity and the flow direction of the medium.