Reserach On Fluid-structure Interaction And Vibration Characteristics Of Centrifugal Pump With Backflow And Cavitation

When the centrifugal pump is running under low flow conditions,the inlet of the impeller will appear backflow.The occurrence of backflow will worsen the flow field,causing unnecessary energy loss,and to a certain extent will also induce the generation of cavitation.Under the interaction,the unstable flow in the pump will be exacerbated.On the one hand,this unstable flow structure will cause the structural characteristics of the over-flow components to change,causing structural fatigue damage;on the other hand,it will cause hydraulic vibration,induced vibration and noise,which will seriously affect the reliability and stability of the centrifugal pump.Therefore,the research on the structural characteristics and vibration characteristics of centrifugal pumps under the action of reflux cavitation and unstable flow has important engineering value and theoretical significance.In this paper,a combination of numerical simulation and experimental research is used to conduct a comprehensive study of the small flow backflow cavitation unstable flow and induced fluid-solid interaction and vibration characteristics of three different impeller scheme centrifugal pumps.The research content and innovation points of this paper as follows:1.Describe in detail the current status of research on backflow,cavitation flow and fluid-solid coupling vibration characteristics in centrifugal pumps at home and abroad,and summarize and analyze the development of backflow cavitation unstable flow and its induced fluid-solid coupling and vibration characteristics.2.Carry out constant simulation research on the model pump,obtain the internal flow field information of the three different impeller scheme model pumps under different flow rates,and analyze the backflow characteristics of the pump.The main conclusions are:the backflow strength at the inlet of the impeller is related to the flow rate and the form of the impeller;The occurrence of backflow will change the vortex distribution inside the impeller and the entrance of the impeller,and at the same time cause the increase of flow dissipation,affecting the energy conversion efficiency of the pump;when the backflow occurs,the static pressure fluctuation at the entrance of the impeller is obvious,and the lowest static pressure appears in the blade tip At 1/4 pipe diameter from the axis of the impeller,backflow vortex cavitation is most likely to occur here.3.Load the cavitation model on the basis of the simulation of the constant simulation results of the model pump,and study the internal cavitation flow characteristics.The influence of backflow on the distribution of cavitation in the impeller is analyzed,and the steady cavitation characteristics under low flow conditions are discussed.The main conclusions are:compared with the optimal operating point,the initial position of cavitation at the blade is changed from the top of the back of the blade to the middle and lower part of the back of the blade under the small flow rate;The asymmetric distribution of cavitation in the impeller flow channel is more obvious,which may be related to the unstable flow of the impeller inlet backflow.4.Based on the ANSYS Workbench platform,a one-way fluid-structure interaction method is used to carry out static and dynamic analysis of different rotor system solutions.The conclusions are as follows:as the flow rate decreases,the maximum equivalent stress of the rotor system of each solution increases continuously,while the maximum deformation The amount will increase first and then decrease with the decrease of the flow rate;coupled with the pressure load of the flow field under different cavitation numbers of 0.6Q_BEPB,it is found that as the cavitation number continues to decrease,the stress on the rotor system and the maximum deformation produced All of them show obvious asymmetric distribution,which may be caused by the non-uniformity of the blade flow field when cavitation occurs at small flow conditions.5.Build a closed-type test stand,and carry out external characteristics and cavitation performance tests on the model pump,and collect vibration singal.Processing and analyzing the data obtained from the experiment,the conclusion is as follows:?1?Compare the numerical simulation prediction results under different impeller schemes with the experimentally measured external characteristics and cavitation performance curves.The two are closer to each other,which verifies the accuracy of the numerical simulation;compares the different impeller scheme heads,efficiency and The cavitation number at the initial stage of cavitation found that the closed impeller scheme has good hydraulic performance,but its cavitation performance is poor,and the long and short blade impeller scheme has poor hydraulic performance but good cavitation performance.?2?Time and frequency domain analysis of axial and radial vibration signals at the impeller inlet and find,Compared with the optimal working conditions,the radial?x direction?and axial?z direction?vibration acceleration amplitudes of the impeller inlet at the impeller inlet at small flow conditions have significantly increased and the overall radial amplitudes are both Higher than the axial direction,the radial vibration amplitude under 0.4Q_BEPAEPA operating conditions is about 4.5 times the optimal operating point;the radial and axial main frequencies of the impeller inlet at each flow rate are integer multiples of the axial frequency,subject to impeller rotor dynamic and static interference Due to the excitation effect,the vibration signal leaf frequency has a large amplitude;the unstable flow of the impeller inlet backflow will affect the characteristic frequency distribution of the vibration acceleration,and at the same time,the vibration signal has a low frequency characteristic when the backflow occurs.Choose 0.4Q_BEPA,?=0.16 working condition to analyze the vibration acceleration at the inlet of the impeller.At this time,the lift coefficient drops by 3%and cavitation occurs.Under this working condition,the amplitude of vibration acceleration in the x and z directions fluctuates greatly with time,and The z-direction amplitude is generally smaller than the x-direction,about 1/2 of it.In the frequency domain analysis,compared with the non-aerochemical conditions,the frequency of high-frequency vibration in the x-direction is significantly increased,and the occurrence of cavitation has exacerbated the unstable flow of the impeller inlet.