Study On The Internal Flow Field And External Characteristics Of Multistage Centrifugal Pump Under The Condition Of Impeller Oscillation

A multi-stage centrifugal pump with a floating impeller is equipped with a hexagonal shaft that drives the impeller and allows it to move axially on the shaft,facilitating stage adjustment and installation.This type of pump is suitable for high lift and small flow rate applications.However,due to the interaction between unsteady fluid dynamics and the impeller structure,the impeller undergoes oscillation,and the effect of impeller vibration on the internal and external characteristics of the multi-stage centrifugal pump is not clear.To address this issue,experimental and simulation methods were used to conduct research and draw conclusions:(1)When comparing the external characteristics of the multi-stage centrifugal pump under impeller oscillation and non-oscillation conditions,it was found that the pump efficiency and lift under impeller oscillation conditions were closer to the experimental values.This indicates that the impeller oscillation condition is more consistent with the actual operating conditions of the multi-stage centrifugal pump.When the impeller moves to the front pump chamber housing,the efficiency of the multi-stage centrifugal pump reaches its maximum value.When the impeller moves to the rear pump chamber housing,the efficiency and lift of the multi-stage centrifugal pump reach their minimum values.Regarding the leakage caused by impeller oscillation,the leakage on the upper pump chamber side changes less with flow rate,but the leakage on the lower pump chamber side decreases with increasing flow rate.The leakage on the upper pump chamber side is greater than that on the lower pump chamber side.When the impeller oscillates to the front pump chamber housing,the leakage on the upper pump chamber side reaches its minimum value,and the leakage on the lower pump chamber side reaches its maximum value.(2)Flow field characteristics of the multi-stage centrifugal pump were obtained under different operating conditions,and the entropy production losses of each flow passage component were analyzed.It was found that the losses inside the impeller mainly concentrated at the inlet leading edge of the impeller blades,and the entropy production losses of the impeller passage increased with the increase of flow rate,with the losses of the secondary impeller being larger than those of the first-stage impeller.The losses in the pump chamber accounted for the largest proportion of the whole pump unit,and the main loss zone was located between the impeller outlet and the pump chamber wall.During the oscillation process of the impeller,the losses at the leakage area would change constantly with the different positions of the impeller.The flow state inside the guide vane was relatively turbulent,especially at the inlet of the guide vane,where the flow lines were chaotic and resulted in more losses.(3)In a multi-stage centrifugal pump,monitoring points were set up to measure pressure pulsation data inside the impeller,pump chamber,and guide vanes.By processing the pressure pulsation data in a non-dimensionalized way and using fast Fourier transform,the timefrequency distribution of the pressure pulsation can be obtained.By analyzing the time-domain and frequency-domain charts of pressure pulsation in the pump under impeller oscillation,it was found that there is only one peak and one trough in the time-domain chart of a monitoring point for one cycle of impeller oscillation,and the peak is located when the impeller oscillates to the front of the pump chamber shell,while the trough is located when the impeller oscillates to the back of the pump chamber shell.From the frequency-domain chart,it can be seen that the main frequency of each monitoring point is the shaft frequency,indicating that the pressure variation inside the pump is influenced less by the rotation of the impeller blades and guide vanes than by the up-and-down oscillation of the impeller.By comparing the pressure pulsation data in the first and second stage pump chambers,it was found that the time-domain amplitude and frequency-domain main frequency at the same position in the second stage pump section are larger than those in the first stage pump section.This indicates that there is a cascading coupling and superposition phenomenon of pressure pulsation in multi-stage centrifugal pumps.