The Research On Dynamic Characteristics Of The Multistage High Speed Centrifugal Pumps Rotors

The characteristics of high speed centrifugal pumps are tight structure and low cost of manufacture, which have a wide range of applications in the chemical industry and in the aerospace engineering. The high speed centrifugal pumps are the main equipments of the rocket fuel supply, the nuclear submarines, the nuclear power plant, the drainage, the military, and agricultural.Currently, the power and speed of the high speed centrifugal pump is higher and higher. In the process of operation, it will inevitably across the first-order even second or the third-order critical speed, running performance is influenced and restricted by the critical speed, especially to the rotors of the multistage pump. In order to guarantee the running smoothly of the multistage centrifugal pump rotor, to avoid the influence of the rotor resonance to the stability and the life of the pump operation, which produced near the rotor critical speed. It must be designed to accurately calculate the critical speed of the working state, namely the critical speed of "wet" condition. By analysis of the internal flow field of the centrifugal pump and the dynamic characteristics of the rotor system in condition of the fluid-solid coupling, and researching the reason of producing resonance, the paper accurately calculate and analyze the critical speed of the rotor in different working operations, to get reliable basis for forecasting the critical speed of the rotor,(effectively restrain or reduce resonance and producing noise.) Thus, this will not only work to improve the reliability of the pump to avoid the occurrence of failure, extend equipment life, and to improve the work environment, improvement of economic efficiency are great significance.Based on studying a3×83/4-10stg HSB high speed multistage centrifugal pump in this paper, calculating the whole three-dimensional steady turbulent flow field by the Fluent software with the standard κ-ε turbulence mode, analyzing the sources of the fluid force and the mechanism of acting on the structure by the fluid force, which include the fluid force caused by fluid flow-induced vibration of the centrifugal pump(such as the pulse of fluid flow), and the fluid forces caused by rotating stall and other instabilities, and the fluid forces caused by interfering between dynamic and static blade and so on. To divide the vibration caused by fluid force into self-excited vibration and forced vibration, and laying foundation of the critical speed calculation. For immersion rotor, the fluid-solid coupling effect not only influence on the flow field and the critical speed obviously. In the paper, through establishment of the element model of multistage pumps rotor and the analysis of the fluid-solid coupling, to discuss the influence of the fluid-solid coupling effect and the spin softening effect on the critical speed. Based on the calculation of the critical speed under rigid supported in this paper, using the finite element model of solid pipe unit (replace the beam unit) and spring elements discussed the influence of natural frequency of rotor by gyroscopic moment, support stiffness and softening effect of fluid respectively, the mouth ring stiffness, axial stress and other effects on the natural frequency of the rotor. Eventually, the each critical speed and the resonance mode of the rotor in the working state have been given. At the same time, several aspects of the experience and understanding are as follows:1. The softening effect of fluid reduced t obviously the critical speed of the rotor, and the high the speed of the rotor is, the obviousness the effect is;2. The stiffness of the supporting bearing and the mouth ring bearing are important factors to the critical speed, simplifying the support stiffness accurately and determining the support stiffness and the damp matrix reasonably can accurate calculation critical speed.3. Due to effecting of the fluid-solid coupling on the "wet" condition of the rotor, the vibration is occured in the interface coupled, It is very difference to the "dry" critical speed.4. The mouth ring bearing which is the most significant to changing critical speed of the rotor is an important factor of the fluid-solid coupling.5. The axial stress can not only improve the rotor critical speed, but also to change the vibration mode and improve the stability of the rotor, It can’t ignored for the "back to back" and self-balancing structure impellers of the multistage centrifugal pumps which impellers are fixed with even number.6. Simplifying the calculation model accurately is basis of getting accurate result, take full advantage of ANSYS model will increase accuracy of simulation and save computing resources.The calculations of the critical speed of the parts of multi-stage centrifugal pump rotor in working condition must takes into account of various factors and different theories, including the knowledge of traditional rotor dynamics, elasticity and the theory of hydrodynamic lubrication and sealing dynamics, which is a very complicated process. The calculation results of this paper are to provide a reference for future research, and to lay the foundation for simulating the critical speed of the high speed multi-stage centrifugal pump rotors.