Analysis And Experimental Study On Dynamic Properties Of Seal-rotor System Of Charge Pump For Nuclear Power

As an important equipment of nuclear power plant systems,multi-stage centrifugal nuclear power charge pumps have a pressure-bearing capacity of tens of MPa.At present,most of the core components of nuclear power charge pumps in China are mainly imported from abroad,and their key core technologies are still restricted.With the development of the equipment to large-capacity and high-performance parameters,the independent intellectual property rights and breakthroughs in key core technologies are great important to the development of China’s nuclear power industry.During the service period of the nuclear power charge pump,due to the seal excited forces,the consequences like large vibration,the wear seal and other failures are common,which seriously affects the safe operation,and the economic losses caused by the shutdown are as high as tens of millions.Therefore,this paper takes the seal-rotor system of the charge pump of nuclear power as the research object,and uses a combination of theoretical analysis,numerical simulation and test to study the dynamic characteristics of the liquid annual seal,rotor motion characteristics,and the dynamic characteristics and optimization of the charge pump rotor,so as to provide the theoretical basis and engineering guidance for the dynamic design and efficient and robust operation of the charge pump of nuclear power.The main work and research results are as follows:First of all,Based on the Navier-Stokes equation,the liquid flow in the pump chamber is approximately equivalent to the axisymmetric two-dimensional viscous laminar flow movement formed by the superposition of the circular tangential flow and the radial differential pressure flow.Considering the fluid loss in the seal clearance,the radial pressure distribution of the liquid in the pump chamber and the pressure distribution expression at both ends of the front and rear seals of the impeller are analyzed.Based on the Bernoulli equation,the mathematical expressions of pressure and differential pressure for multi-stage seals are finally derived.Through similar theories,a single-stage pump test platform is built and a CFD analysis model of the full flow field is established.The reliability of the theoretical model is further verified from the perspective of experiments and CFD numerical analysis,the axial,peripheral and radial distribution of pump chamber pressure are studied.The research results can provide a theoretical basis for the analysis of sealing dynamics and nuclear power charge pump dynamics.Secondly,In order to improve the calculation accuracy and calculation efficiency of the dynamic coefficient of the liquid annual seal,the UDF function DEFINE＿CG＿MOTION is used to establish the rotor rotating motion equation and the DEFINE＿PROFILE macro command to establish the rotor whirling motion equation.Through the response surface analysis and CFD method,the seal size parameter was optimized,and the whirl-frequency ratio decreased after optimization.Based on the thermo-fluid-solid coupling model,the effects of temperature,pressure and centrifugal load on the deformation and rotordynamic coefficients of the seal structure are studied,and the seal leakage is verified by building a seal test rig and the rotor vibration is also tested.Again,Based on Capone bearing theory and Muszynska nonlinear dynamics model,a single-disc rotor-bearing-seal coupling dynamics model is established.In order to obtain more accurate dynamic parameters,the seal flow field and pressure distribution at different eccentricities and different rotational speeds are solved by CFD method.The approximate function surface of the seal dynamic parameters are obtained by fitting the Radial Basis Function Method is used,and the dynamics equation is substituted and solved by the Runge-Kutta method to obtain the nonlinear motion characteristics of the rotor system.The influence of seal structure parameters on the nonlinear motion characteristics of the rotor is carried out,and the stability analysis of the maximum Lyapunov index is done.As the hydraulic head condition increases,the chaotic area of rotor movement decreases,the maximum Lyapunov index is less than 0,the stability of the rotor increases.Then,Based on the rotor dynamics theory,the finite element method is used to establish a dynamic model of the rotor-seal system of the nuclear power charge pump.The Newmark method is used to solve the critical speed,mode,logarithmic decrement rate and unbalanced response amplification factor of the rotor shaft system of the charge pump under different operating conditions.It is shown that the seal has a great impact on the first-order critical speed of the rotor system.When the hydraulic head condition increases,the vibration response value decreases.Finally,Based on the optimal Latin hypercube design method,a sample of the seal parameters of the BP neural network is established,and the predicted value is compared with the calculated value.The results show that the maximum relative error of the critical speed value and the logarithmic decrement rate is 1.04% and0.76%.Using the BP neural network model as the fitness function of the NSGA-Ⅱ algorithm,the first-order critical speed value and logarithmic decrement rate are optimized within the sample range,and finally the optimization scheme with the best overall performance is obtained.The “wet” critical speed test has verified the method.