| In recent years,it has been found in engineering practice that the pump rotor structure of large pump stations is often damaged and resonant,the blades are cracked,and the pump shaft slips back and forth or shakes up and down.These problems seriously affect the safety and stability of pump stations.Therefore,based on fluid structure coupling,modal analysis theory and dynamic grid technology,this paper systematically studies the structural mechanics characteristics of the pump rotor by using numerical simulation methods,taking the largescale planar S-type axial flow pump station Wangdao pump station of the Yellow River to Qingdao Project as the research object,and provides theoretical reference for the structural optimization design of the pump unit of large-scale pump stations.This article constructs a numerical calculation model for a planar "S-shaped" axial flow pump device,studies the pressure distribution characteristics of the suction and pressure surfaces of the blades,and explores the stress-strain distribution law of the blades under different radii based on unidirectional fluid solid coupling;Modal analysis is used to study the vibration mode and frequency of the rotor structure,and check the resonance;The mathematical model reveals the influence of different diameters on the natural vibration frequency of the rotor;Based on the dynamic grid technology,the bearing water film characteristics under different eccentricity of the pump shaft are obtained.The main primary coverage are as follows:(1)Using Creo to construct a three-dimensional fluid domain,using ICEM mesh partitioning,and using CFX solver and CFD-Post post-processing software,the characteristics of the water pump device at three blade angles(-4°,0°,+4°)were numerically analyzed,and the feasibility of the numerical calculation model was experimentally verified.The pressure distribution on the blade and the changes in radial and axial forces were obtained through three-dimensional turbulent numerical calculations.The pressure analysis on the three cylindrical cross-section airfoils of the blade(r=0.4m,r=0.6m,r=0.8m)showed that the extreme pressure difference on the blade was located at the inlet edge of the blade.As the flow rate increased,the extreme pressure difference decreased,and as the blade angle and radius increased,the extreme pressure difference increased;The axial force decreases with the increase of flow rate,but increases with the increase of blade angle;There is no significant correlation between radial force,flow rate,and angle.(2)The three-dimensional solid domain of the rotor is constructed through Creo.and the mesh is used for solid grid division.Based on the static structural software,the blade pressure is received and the solid Statics analysis is carried out.The blade stress and strain at different angles and flow rates and the stress and strain at different radius sections of the blade(r=0.4m.r=0.6m.r=0.8m)are analyzed.The results show that the maximum deformation occurs at the flange of the inlet edge of the blade,and the maximum deformation is 1.99mm.The maximum equivalent stress at the root of the blade is 70.22MPa,which is less than the material strength.The maximum deformation variable and maximum equivalent stress decrease with increasing flow rate and increase with increasing angle.As the radius of the blade decreases,the maximum deformation on the outer edge of the radius section gradually moves from both sides of the water inlet edge to the back side of the blade axis center.The maximum equivalent stress gradually moves from the surfaces on both sides of the water inlet edge to the upper and lower surfaces of the blade axis center.The minimum equivalent stress is always distributed in a crescent shape on the connection line of the water inlet and outlet edges of the section.(3)Using modal software to conduct modal analysis of the rotor,the vibration mode and frequency of the rotor were analyzed,and the accuracy of numerical calculation frequency was verified through experiments.Through transient calculation of axial force,radial force,time and frequency domain diagrams of pressure at different radii of impeller inlet and outlet and guide vane outlet using CFX,the influence of different impeller diameters(3m,2.7m,2.4m,2.1m.1.75m)on the natural mode of the rotor was analyzed,The results indicate that the most resonant parts of the rotor are the blade edge,water guide cap,and pump shaft.The inherent natural vibration frequency of the rotor structure of Wangdao Pump Station is 48Hz.The time domain chart shows that the axial and radial forces fluctuate periodically,and the radial force components have significant hysteresis.The inlet pressure of the impeller is greater than the outlet pressure of the impeller and the outlet pressure of the guide vane,and the pressure fluctuation amplitude of the impeller outlet is significantly greater than that of the impeller inlet and guide vane outlet.The characteristic frequencies during the operation of the pump station are:single blade rotation frequency is 3.43Hz,impeller rotation frequency is 10.315Hz,guide vane rotation frequency is 17.19Hz,axial and radial force main frequencies are 20.63Hz.pressure pulsation main frequency at the inlet and outlet of the impeller is 3.43Hz,and pressure pulsation main frequency at the outlet of the guide vane is 10.315Hz.The above characteristic frequencies are much smaller than the natural vibration frequency of the rotor.so the rotor will not produce resonance.The larger the diameter,the lower the natural vibration frequency of the rotor.Therefore,when the impeller diameter is 3m.resonance is easily generated.(4)By writing a UDF program and using dynamic grid technology,fluent software was used to analyze the pressure velocity time-domain and frequency-domain characteristics of non centrifugal water films at different rotational speeds(206.3r/min,186.12r/min,173.42r/min,164.86r/min.156.29r/min).fluent software was used to analyze the force on water films at different rotational speeds and centrifugal rates(0,0.2,0.4,0.6,0.8),and to compare the water film support force with the pump shaft radial force.The results show that when the water film has no eccentricity,as the pump shaft rotates,it drives the water film near the pump shaft to rotate.The maximum pressure area distributed on the water film shows a patchy distribution,and the velocity shows a circular distribution.As the speed increases,the maximum pressure and minimum pressure first increase and then decrease.The extreme pressure difference keeps increasing and is approximately linearly related to the speed:p=1.30878n-146.175.The proportion of the maximum speed area and the speed are linearly related:a/a0=0.338544n-36.3989.The time-domain diagram of the pump shaft force shows noise like fluctuations,with a maximum dominant frequency of 5Hz in the frequencydomain diagram,which is lower than the natural vibration frequency of the rotor.Therefore,the water film force will not cause resonance of the pump shaft.When the water film has a eccentricity,as the eccentricity increases,the extreme pressure difference increases sharply,increasing by 21.15 times;As the speed increases,the extreme pressure difference gradually increases,increasing by 0.66 times.As the rotational speed increases,the water film force on the pump shaft gradually increases by 0.67 times;As the eccentricity increases,the force increases sharply,increasing by 502.95 times.The eccentricity has a significant impact on the water film force and extreme pressure difference.When the eccentricity is greater than 0.6,the gradient of water film force significantly decreases.The force is linearly related to the speed.The support force provided by the water film to the pump shaft is 100.79N,which is less than the radial force,so the pump shaft will generate dry friction with the water guide bearing. |
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