| Multistage centrifugal pump is composed of multiple impellers in series, and it has many advantages, such as running with safety, stability and low noise, along with long operating life,easy installation and maintenance. It is widely used in petrochemical, electric power, urban water supply system and other fields. With the continuous development of industrial technology, the development of centrifugal pump with high speed, high power and high power density ratio, so the speed of rotators will close to even over the critical speed which will inevitably cause resonance; moreover, even under the normal operating condition, the unsteady excitation of fluid could leads to pump vibration, all these will have a serious impact on the safe and stable operation of multistage centrifugal pump. Therefore, it is very important and valuable to conduct modal and vibration analysis of the rotator system which based on one way fluid-structure interaction.In this paper, the commercial software Pro/E is used to model the whole flow passage of four stages centrifugal pump including its double volutes. Numerical calculation results of the steady flow in the centrifugal pump are used as the initial conditions of the unsteady flow based on fluid-structure interaction.. The main research contents are as follows:(1) In order to analyze the internal unsteady flow characteristics of the multistage centrifugal pump and based on Realizable k-? turbulence model, the unsteady flow fields of multistage centrifugal pump which under different operating conditions are numerically simulated, the static pressure and velocity distributions with time in every stage impeller and volute are investigated. Moreover, the results of external characteristic between numerical simulation and experiment are consistent which can verify the calculation results.(2) In order to analyze the characteristics of double volute structure and the effect of rotor-stator interaction, the pressure fluctuations at the monitoring points on every stage volute are analyzed, the results show that the change of relative position between impeller and tongue,and the interference of tongue will affect the formation of the peaks and valleys of the pressure fluctuations; the time series of pressure fluctuations at different monitoring points are related to the number of impeller blade and the interference of tongue in every stage volute; due to theinterference of volute tongue, the pressure fluctuations near the tongue are influenced more seriously.(3) In order to analyze the impeller radial force, the cause of radial unbalance force and the interference of the tongue on the radial force, the radial force of single blade and impeller are analyzed. Results are as follows: when the blade trailing edge sweeps across the tongue, a sudden change of radial forces occurred on all impellers and blades. With the increase of flow rate, the fluctuations of the radial force decreased. The unbalance of the radial forces are affected by the radial force of impeller blades, also by the radial unbalance force of the front and back cover plate which caused by the static pressure distributions asymmetry in volute passage.(4) The modal analysis results of multistage pump rotor system under wet and dry modal analysis and in consideration of pre-stress on structure during fluid-structure interaction are carried out. It is found that, the critical speed of rotation is increased when taking the fluid sealing force into consideration, and the amplitude of vibration decreased when taking the pre-stress of fluid-structure interaction into consideration.(5) The changing of the equivalent stress and maxim shear stress with time at different flow rates, and the vibration data of the centrifugal pump rotator system are analyzed. It is found that,the radial excitation force is closely related to the radial vibration of the rotor system, the vibration caused by the axial force of the fluid is calculated and partial frequency results of the test are in good agreement with the experimental results. |
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