Unsteady Flow And Vibration Characteristics Of M Ultistage Centrifugal Pump Based On Large Eddy Simulation

Multistage centrifugal pumps are widely used in petrochemical and power industries and other industries,and are indispensable and important fluid transportation equipment for the national economy.At present,multistage centrifugal pumps are developing in the direction of higher head and higher speed,but the vibration,noise and stability of the running process are the core issues that restrict their development.One of the main sources of centrifugal pump vibration is the unsteady fluid exciting force that generates by inner complex flow and pressure pulsation that induces by dynamic and static interfere.Therefore,based on the high-precision internal flow field information,it is of great significance to analyze the unsteady flow and fluid excitation in the multistage centrifugal pump.In this paper,the large eddy simulation method is used to numerically calculate the unsteady flow of the multistage centrifugal pump.The internal flow,pressure pulsation characteristics and axial and radial excitation force rules induced by the unsteady flow are obtained.The vibration response of the bearing surface of the rotor system under the action of unsteady radial fluid excitation force is further analyzed to reveal the vibration source of the multistage centrifugal pump rotor system.The main content of the paper is as follows:(1)Using UG to establish the three-dimensional full-flow field fluid domain and rotor structure model of multistage centrifugal pump,meshing the fluid domain and rotor system respectively.The steady and unsteady flow of the whole watershed were calculated,at the same time,the modal and the vibration characteristics of the rotor were analyzed.(2)Through the analysis of the inter-stage head characteristics and internal flow of the centrifugal pumps in different flow conditions,it is found that the difference in inlet speeds is one of the reasons for the differences in the characteristics of the pumps at all stages;at the design conditions,the single stage head of 6 stage is the highest,and the speed of its inlet is the largest.When running away from the design conditions,the distribution of the inlet flow field at all stages of the pump is more uneven.(3)By studying the time and frequency domains of pressure pulsation at the inlet and outlet of the multi-stage centrifugal pump at the design flow rate,the outlet of the impeller,and the gap between the front and rear cover plates,it is found that the frequency of pressure pulsation at different positions of the impeller are mainly at the blade passing frequency,the amplitude of pressure pulsation near the front cover plate wall is the largest;the pressure pulsation at different circumferential positions of the impeller outlet are mainly at the blade passing frequency and its doubling frequency;among them,the amplitude of pressure pulsation at the final inlet and outlet are the largest;The pressure pulsation in the gap between the front and rear cover plates is mainly based on twice the blade passing frequency and the axial frequency.(4)Through the analysis of the fluid excitation force on the impeller induced by the unsteady flow in the multi-stage centrifugal pump,it is found that the axial force experienced by the impeller at each stage has a certain difference,and the total axial force increases with the increase of the flow rate;The radial fluid excitation force acting on the impeller is most the axial frequency and the blade passing frequency.As the flow rate increases,the amplitude of the main frequency of the impeller radial force at all stages gradually decreases.(5)Through the calculation of the critical speed of the rotor system of the multistage centrifugal pump,the modal vibration mode and the analysis of the vibration characteristics of the shaft were analyzed to analyze the action of the fluid excitation force,it is found that the critical speed in the "wet" is significantly greater than the critical speed in the "dry";The maximum deformation of the modal shape under "wet" is less than that of the "dry";when deviating from the design flow conditions,the vibration response displacement of the non-driving side of the rotor is larger.