Research On Bearing Lubrication Characteristics And Rotor Dynamics Of Vertical Volute Pump

Large vibration and high noise are the main problems of large vertical volute pumps.The rotor-bearing system as the core component of the vertical volute pump significantly affects the stability of the pump.Therefore,it is necessary to analyze the dynamic characteristics of the rotor during operation.Since the guide bearing as the decisive part of the pump rotor system,in order to ensure the bearing capacity in the process of operation,it is necessary to analyze its static and dynamic characteristics.In order to improve the running state of the vertical volute pump and increase the stability of the rotor,the radial force variation rule was studied on the basis of analyzing the internal flow field of the pump.The dynamic and static characteristics of the guide bearing were calculated.Compared the dynamic response characteristics of the rotor of single and double volute pump.The results can provide basis for the structural optimization design of the vertical volute pump.The main research contents and achievements of this paper as follows:(1)The hydraulic components of the vertical volute pump were designed and simulated to analyze the internal pressure fluctuation of the volute and the radial force of the impeller.It is found that the rotor-stator interaction between the impeller and the volute is the main reason for the pressure pulsation in the pump.The pressure pulsation and the radial force of the impeller change periodically.The frequency of radial force include shaft frequency and blade frequency.(2)The guide bearing was designed according to the force of the rotor structure.The static characteristics of the bearing including oil film pressure,oil film thickness and friction torque were analyzed by COMSOL software.The small disturbance method is used to analyze the dynamic characteristics of bearing stiffness and damping based on MATLAB.The results show that the maximum pressure and friction torque are negatively correlated with the clearance and positively correlated with the width-to-diameter ratio and the viscosity.Amongthe three parameters of clearance,width-to-diameter ratio and viscosity,width-to-diameter ratio has the greatest influence on bearing capacity,stiffness and damping.(3)The one-dimensional beam model and three-dimensional solid model of vertical volute pump rotor were established,and the critical speed was calculated by using COMSOL.The results show that there is little difference between the two models in critical speed and mode shape.The critical speed is much higher than the operating speed.The gyro effect of the rotor is obvious,and the first mode of the rotor is mainly manifested as the bending deformation of the impeller.(4)The transient response of the rotor-bearing system of the vertical volute pump under the "wet state" was calculated,the vibration displacement and the axis trajectory of the rotor system,the pressure distribution and the oil film thickness distribution of the bearing under the transient state were analyzed.The results show that the peak-peak value of vibration at the bearing is larger than the required value of API standard at the operating conditions of0.6Q,0.8Q,and 1.4Q.The vibration frequency of the rotor in the vertical volute pump under "wet state" is not only half-frequency and shaft frequency but also blade frequency.The maximum oil film pressure value of the guide bearing changes continuously with time.Under design and off-design conditions,the minimum oil film thickness value is higher than the allowable value.(5)The double volute model was established.The transient response of the rotor-bearing coupling system of double volute was calculated.The double volute can not only maintain the hydraulic performance of the pump,but also significantly reduce the radial force.The peak-peak values of the vibration at the bearings under various operating conditions of the double volute are all less than the required values in the API standard.Compared with single volute,the effect of double volute on reducing rotor vibration is very obvious.Under 0.6Q operating conditions,the peak-peak value at the bearing is reduced by39.56%,and the total displacement at the impeller is reduced 15.17%.It shows that the double volute can obviously reduce the vibration displacement of the rotor system and improve theoperational stability of the rotor.