Numerical Study On Flow Characteristics Of Internal Flow Field Of Centrifugal Pump Based On Dynamic Mode Decomposition

The submerged centrifugal pump is the core component of the system produced by the chemical industry.It is a key problem for us to ensure the safe and stable operation of the submerged centrifugal pump.The unsteady flow in the centrifugal pump often induces the vibration and noise in the pump,thus affecting the stable operation of the centrifugal pump.Therefore,in-depth study of unstable flow in centrifugal pumps will help us to improve the operating environment of submerged centrifugal pumps and make them work more stably and reliably.In this paper,a submerged centrifugal pump produced by a domestic company was studied.The numerical calculation method and dynamic mode decomposition method(DMD)were used to study the unstable flow phenomenon of the internal flow field.This paper mainly does the following research work:Firstly,the flow law of the internal flow field of the submerged centrifugal pump under different flow conditions was calculated by numerical simulation method.The variation of the external characteristics of the centrifugal pump under numerical calculation and test results was also compared.The results show that the numerical calculation and the external characteristic curve of the submerged pump obtained by the test are in good agreement.The trends of the head,shaft power and efficiency of the two methods are basically the same.Under low flow rate conditions,the internal flow state of the pump is the worst,and the pressure distribution near the tongue and the inlet of the partition is relatively messy,and the area with larger turbulent energy is mainly concentrated in these two areas.Under the condition of large flow rate,as the flow rate increases,the backflow phenomenon of the volute outlet becomes more and more obvious,and the backflow phenomenon gradually appears at the entrance of the partition.Secondly,based on the previous constant calculation,the internal flow field of the centrifugal pump under the third flow conditions of 0.6 Q_d,1.0 Q_d and 1.4 Q_d was calculated unsteadily,and a series of monitoring points were selected for the centrifugal pump.The pressure pulsation inside has been studied in detail.As a result,it was found that the pressure pulsation caused by the impeller blades when passing through the same circumferential position is substantially the same,and the rotor-stator interaction is the most important factor causing the pressure pulsation in the impeller flow passage.The maximum amplitude of the pressure pulsation at each monitoring point in the volute appears at the 1X blade passing frequency,and the pressure pulsation amplitude at the volute tongue is the largest.Starting from the volute tongue,along the spiral section of the volute to the fourth section of the volute,the maximum pulsation amplitude at each section monitoring point is reduced accordingly,but the highest pressure pulsation at the entrance of the slab The amplitude suddenly increases and then decreases along the spiral section of the volute.At the volute tongue,when the flow rate is reduced,the separation flow of the fluid medium here will dominate the generation of pressure pulsations in this area.Finally,on the previously unsteady calculated flow field data,the dynamic mode decomposition method was used to study the flow field structure of the submerged pump in the volute under low flow rate conditions and rated conditions.The results show that the DMD method is used to analyze the unsteady flow under rated conditions and small flow conditions,and the flow modes corresponding to the characteristic frequency and other frequencies are extracted,and the reduced order analysis of the original flow field is realized.The first-order modes under both operating conditions are the flow structures occupying the dominant position of the original flow field.The second and third-order modes of the two are the main oscillation modes of the original flow field,and their characteristic frequencies are The 1x blade passing frequency and the 2x blade passing frequency obtained by FTT are consistent,which proves that the rotor-stator interaction between the impeller and the volute is the main reason for the unsteady flow in the volute.Comparing the various modes of velocity contours under the two conditions,it can be seen that when the flow rate of the centrifugal pump is reduced,the existence of the tongue and the partition plate is more likely to cause unstable flow of low frequency inside the volute.