Research On The Clearance Flow And Dynamics Characteristics Of Cantilever Multistage Centrifugal Pump

Due to the unique compact structure,cantilever multistage centrifugal pump is widely used in military and civilian high space requirement field.In view of the cantilever shaft and impeller are far from bearing support and partial to one side,the rotor system of cantilever multistage centrifugal pump is easily to occur the phenomenon of radical deflection and unsteady whirl motion under unbalanced load.The clearance leakage,which refer to the flow between rotating impeller shroud and stationery pump housing cover and the flow in wear-ring,is one of the most important source of excitation force.Thus,the influence of clearance flow on the cantilever multistage centrifugal pump cannot be neglected,and detailed studies of the clearance flow and its dynamic characteristics are necessary.Aiming at the sidewall clearance flow of multistage centrifugal pump,five-stage centrifugal pump was selected as the research object to analyze the clearance internal flow,dynamics characteristics and the influence of clearance flow on the stability of rotor system.A series of experiments were carried out to investigate the influence of clearance flow on the rotor performance simultaneously.The main research contents and conclusions are outlined as follows:(1)Based on CFX 14.5 the whole flow field with clearance leakage of cantilever multistage centrifugal pump was calculated.It is showed the predicted pump performance curves present good agreement with the experimental ones,indicating the numerical prediction of performance is accurate.The influence of the clearance flow on the main flow field in the pump was analyzed.It shows,under low flow rate condition,clearance flow has the most obvious influence on the pressure,velocity and turbulent kinetic energy distribution.(2)Based on the M220 clearance leakage model,four kinds of clearance flow channels were constructed to studied the relation between the energy distribution of the clearance flow and the clearance structure by analyzing the pressure pulsation.It is found that the existence of wear-ring and inter-stage seal enlarges the amplitude of the main frequency of the front and rear pump chamber.The pressure fluctuation in the front chamber gradually enhance from outer diameter to inner diameter along the clearance channel,in contrast,the rear pump chamber has an opposite trend.(3)A computational fluid dynamics(CFD)code was employed to study the influence of the axial displacement of impeller,casing the change of pump chamber meanwhile,on the external characteristics,the energy characteristics,the flow in the front chamber,the pressure fluctuation and the axial and radical force of cantilever multistage centrifugal pump.Through the comparison,it shows the variation of clearance in the front pump chamber has a greater impact on the external characteristics,and the change of clearance in the rear pump chamber effects on the axial force most obviously.(4)Established the overall calculation model including the wear-ring seal and the impeller shroud fluid-filled gap to solve the rotor dynamic force,and verify the accuracy of the method for solving the dynamic characteristic coefficient of the clearance flow based on the experiment results;The dynamic characteristic coefficients of the clearance flow of cantilever multistage centrifugal pump were solved based on the second perturbation equation.To consider the influence of clearance flow,dynamic coefficients of clearance flow in the design condition were introduced into the modeled rotor system of the cantilever type multistage centrifugal pump through matrix transformation.The critical speed and the imbalance response were calculated under the two conditions of with and without taking clearance flow into consideration respectively,the results show that the clearance flow has a supporting effect for the rotor system,improving the stability of the rotor system.(5)In order to predict the influence of clearance flow on the vibration performance of cantilever multistage centrifugal pump directly,the experiment platform of the vibration and axis orbit of cantilever multistage centrifugal pump were designed and established.Based on the test facility,the vibration of pump body and the axis orbit of the rotor system were measured under different flow conditions.It shows the rotor system exists mass unbalance at run time.Under the large flow condition,the rotor system is the most stable compared with other condition.Oppositely,the phenomenon of misalignment occurs under the low rate condition,the influence of clearance flow is obviously.The experimental results provide a reference for the optimization design of the cantilever multistage centrifugal pump.