Rotor Dynamical Characteristics Analysis Of LNG Cryogenic Submersible Pump Based On Thermal-fluid-solid Coupling

As a new type of clean energy,LNG has been widely used in the world and gradually becomes one of the pillar energy which is in parallel with petroleum and coal.During the process of mining and transportation in LNG,LNG cryogenic submersible pump is the most important power equipment.Its operating temperature is-162?.Under the effect of low temperature,the rotor part will shrink and deform,which will lead to the pump jamming and abnormal operation.So it is of great significance to study its dynamic characteristics.In this paper,a LNG cryogenic liquid pump was used as its Research goals,optimized the impeller and guide vane of LNG cryogenic liquid pump.In addition,the stress distribution and thermal deformation of the rotor components of the pump at different flow rates and different temperatures were studied.And check the strength of rotor components.Meanwhile,the modal analysis of the rotor parts of the pump is carried out in dry state without prestressing,dry prestressing and LNG medium.On the basis of modal analysis,the critical speed of each stage is analyzed to predict the possibility of resonance of the pump during operation.Finally,based on the modal analysis,the harmonic response analysis is performed to analyze the influence of unbalanced loads on the displacement amplitude and acceleration amplitude.Provides design basis and guidance for safe and reliable operation of LNG cryogenic submersible pump.The main research work and achievements of this article are as follows:(1)According to the design goals,three sets of hydraulic model solutions have been designed,the pump's external characteristics and internal flow field is predicted based on CFD method.The first set of hydraulic solutions is preferred.Numerical simulation results show that at the junction of the impeller exit and guide vane of LNG cryogenic submersible pump,a relatively large energy loss occurs due to the interference of motion and static,from the kinetic energy diagram,it can be seen that the turbulent energy in this position is relatively large.Through the rectification action of the diffuser section of the guide vane,the flow of the liquid gradually becomes stable,and the corresponding turbulent kinetic energy gradually becomes smaller.The flow is unstable under small flow conditions and a small amount of vortices are generated during the flow.At the secondary guide vane,there is no rectification of the vanes,which causes backflow at the vane outlet.(2)Based on thermal-fluid-solid coupling method,The rotor components are subjected to numerical calculation of the thermal-fluid-solid coupling at different flow rates at the same temperature,It is found that when the temperature is the same,the thermal deformation of the rotor component of LNG cryogenic liquid pump under the effect of the heat-fluid coupling force increases with the increase of the flow rate,but the change trend is not obvious.So the flow has little effect on the thermal deformation of the rotor components.Under the same flow conditions,the farther away from the bearing,the greater the corresponding thermal deformation is.The total deformation is decomposed into radial deformation,circumferential deformation,and axial deformation in cylindrical coordinates.Among them,the axial deformation is the largest,the circumferential deformation is the smallest,and the radial deformation is between the two.The axial deformation and radial deformation are mostly manifested as shrinkage deformation.The axial deformation at each position on the rotor component is numerically close to the total deformation,so the axial deformation is the main deformation mode of the LNG cryogenic liquid pump.The equivalent stress on the rotor component decreases with the increase of flow rate,and its safety factor increases gradually.In order to ensure the safe and reliable operation of the pump,the pump should be avoided to run under small flow conditions.(3)A thermal-fluid-solid coupling analysis is carried out for the rotor components at different temperature at the same flow rate,As a result,it is found that when the flow rate is the same,the thermal deformation of the rotor component of LNG cryogenic submersible pump under the influence of the heat-fluid coupling force increases with decreasing temperature,and the change is obvious.This shows that the temperature has a great influence on the deformation of the rotor components,so the temperature is the main cause of the deformation of the rotor components.The temperature range in which the LNG is in the liquid state is relatively small.In this temperature range,the equivalent stress at each position of the rotor component does not change significantly,and the strength of the rotor component can meet the requirements at each temperature.(4)In order to improve the safety and reliability of LNG cryogenic submersible pumps,modal analysis of the rotor parts of the cryogenic submersible pump is carried out in dry,non no stress,dry,stress and LNG media respectively.Comparing the calculated results,it is found that the distribution law of each order natural frequency of the rotor component does not change under the effect of the heat-fluid coupling force and the LNG medium,but the value of the natural frequency changes correspondingly.The influence of the heat-fluid coupling force on the natural frequency of the rotor component is not significant.In the LNG medium,the natural frequencies of the rotor components are significantly reduced by the damping effect of the LNG medium,and the amplitude is reduced by about 5%.(5)The pump speed is much less than 80% of the first-order critical speed,the pump's hydraulic excitation frequency is within the safety range,and the motor's excitation frequency is far less than the first-order torsional frequency of the rotor components.Therefore,the design of the LNG cryogenic submersible pump rotor component meets the requirements of critical speed.(6)Based on the modal analysis,the harmonic response of the rotor components is analyzed to analyze the influence of unbalanced loads on the displacement amplitude and acceleration amplitude.After adding the unbalanced load,when the frequency reaches the frequency corresponding to the first critical rotational speed,the displacement amplitude and acceleration amplitude reach the maximum at each position of the rotor component;Under the same load,the farther away from the bearing,the greater the maximum displacement amplitude and acceleration amplitude;The greater the unbalanced load at the same position,the greater the maximum displacement amplitude and acceleration amplitude on the rotor components.When multiple unbalanced loads act at the same time,the greater the phase difference of the unbalanced loads,the smaller the corresponding maximum amplitude of displacement and acceleration amplitude.