Research About Unsteady Characteristics Of The Flow Field In A Multi-stage Centrifugal Pump Based On The Phase Staggered Of The Impeller

Multi-stage centrifugal pump is the integration of multiple single stage centrifugal pump into a whole,which saves the space occupied by the pump,the pump also improves the operation and maintenance costs.Widely used in water conservancy,chemical production,oil transportation,reverse osmosis desalination and nuclear power and other fields.However,after the series as a whole not only increases the complexity of the whole system,the difficulty of multistage centrifugal pump design will increase,and various instabilities and problems will appear.Internal flow field of multi-stage centrifugal pump is much more complex than single-stage centrifugal pumps,prone to large pressure pulsation is mainly due to the tongue and the blade or vane movement generated interference causing pressure pulsation generation.Interference in the internal incentive exists pump may often be the fatigue strength of each part adversely affected,so to understand the flow characteristics of the flow field inside the multistage centrifugal pump has positive significance of this type of pump design.In this paper,four groups model was designed for the numerical simulation of the internal flow field and the rotor force of the multi-stage centrifugal pump.Scheme A: impeller phase not staggered;Scheme B: impeller phase staggered 1/2 of a impeller flow channel;Scheme C: impeller phase staggered 1/(Z-1)of a impeller flow channel;Scheme D: impeller phase staggered 1/(Z-1)of a Leading vane channel.(Z is impeller blade number)1.Through the unsteady calculation results obtained with the characteristics of different schemes,the external characteristics of the four schemes had little difference;but different schemes of the external characteristics of the characteristics of unsteady often characteristics appear relatively large changes,under different flow head,efficiency,shaft power variation and trends vary under different flow rate.Under the 0.6Q_d?1.0 Q_d working condition superposition of internal incentive Scheme B is better than Scheme A;Under the 1.4 Q_d condition,the intensity of internal interference excitation is weakened,and impeller phase staggered affect the head fluctuation frequency.The maximum fluctuation amplitude of efficiency change under design conditions,and the fluctuation of the efficiency of B and C are relatively ideal under the condition of partial working conditions.Under the three conditions,the power fluctuation of the C and B is relatively stable,and the unsteady shaft power of the scheme B is most stable under the large flow rate condition.Impeller phase change has influenced external characteristics,while the characteristic changes is caused by the internal interference excitation induced,so the change of characteristics can reflect the interference of internal incentive superimposed changes.2.Through the analysis of leading and posterior vane flow monitoring points pressure pulsation found that the pressure fluctuation in the flow passage leading leaves the fluid pulse is mainly affected by disturbance action in front of the guide vane impeller blades,the back guide blade runner in the fluid at the same time from the level of the impeller blade and the lower level of impeller blades together,before and after the two stage impeller form two interference sources at the same time,the fluid flow inside the guide vane until after the disturbance.Flow analysis of internal flow field was found near the main pulsation in the previous stage at the outlet of the impeller vanes being runner is subject to pre-stage impeller outlet blade disturbances before the fluid flow path in posterior vane at the same time an impeller outlet blade and impeller blade inlet under a common effect caused by pressure changes.On export extension section of the monitoring points of the pressure change analysis,scheme B? C?D with the increase of flow pressure change tends to be stable,the impeller phase staggered pressure changes of outlet to a stabilizing role.3.The impeller phase staggered makes the rotor stress vector distribution more concentrated,and the radial force to the axial center,which effectively reduce the radial force of the rotor.Under the condition of 0.6 Q_d scheme A radial force fluctuation frequency,radial stress values are significantly higher than other three scheme,and axial force scheme A,C,d wave with low frequency and 1 times the blade frequency fluctuation dominated,Scheme B is mainly based on low frequency fluctuation.In 1.0 Q_d conditions,the four schemes,significant fluctuations in the similar trends,schemes B,C fluctuation amplitude of the axial force is relatively smaller,at 1 times the blade frequency.In 1.4 Q_d condition,the fluctuation of the four schemes is obvious,and the amplitude of the axial force change is not large,and it is accompanied by a large number of high frequency fluctuations.In summary,The flow field of multi-stage centrifugal pump is changed by the phase of the impeller,and the unsteady characteristic of the external characteristic can also be changed.At the same time,the force of rotor is improved by the impeller phase change.