Study On Dynamic Characteristics Of Rotor-Baring-Seal System Of Ultra-Supercritical Steam Turbine

1000 MW turbine has become the main force in the power generation industry because of its advantages of low coal consumption rate,low emission,high benefit ratio and flexible operation.However,with the capacity of the unit increases,the steam parameters increase easily to cause strong seal steam flow excited phenomenon.Therefore,it is necessary to study the motion and vibration characteristics of the turbine rotor under the influence of the sealed steam flow to lay a theoretical foundation for the design and optimization of the unit.The main work of this paper is as follows:Firstly,the equations of motion of rotor-bearing system were derived and solved by Runge-Kutta method.The rotor motion characteristics affected by different factors in the process of turbine impact speed were studied.The results show that the rotor experiences periodic motion,quasi-periodic motion and chaotic motion successively under different factors.After a large "step" phenomenon occurs within a certain speed range,the stability is restored to the rated speed.With the increase of shaft length and mass eccentricity,the nonlinear degree of the system increases and the stability decreases,while the change of bearing radial clearance has a certain promoting effect on the stability of the system.Secondly,the diaphragm sealing model of a 1000 MW steam turbine unit was established.The multi-frequency whirl model and mesh deformation technology were used to calculate the steam flow exciting force under different operating conditions and sealing parameters by FLUENT,and the formula was fitted to the sealed steam flow exciting force.A rotor-bearing-seal system was established to solve the equations of motion of the coupled sealed steam flow excitation force,and the influence of the sealed steam flow exciting force on the rotor dynamic characteristics was analyzed.The results show that the influence of steam flow exciting increases with the increase of load.With the increase of pressure ratio and seal clearance and the consideration of nonlinear stiffness,the system experiences the transition from chaotic motion to chaotic "two-period" motion to chaotic motion.The loose fault leads to the more disordered motion law of the system and the jump change of scatter displacement.In the spectrum diagram,when the pressure ratio and sealing clearance increase and the nonlinear factors are taken into account,the "dense frequency phenomenon" occurs,while the power frequency component of 1/2 increases and the power frequency component of 1/3 and 2/3 appears in advance.The average Lyapunov index of the corresponding system increase by 16.33%,16.5%,16.9% and 42.9%,respectively.The increase of seal tooth thickness can reduce the displacement span of the rotor,reduce the amplitude of the 1/2power frequency of the system,weaken the vibration of the half power frequency,and delay the occurrence of the derive 1/3 and 2/3 power frequency.System average index decrease by 23.89%.Finally,the lumped parameter method was used to model the high-pressure cylinder rotor of a steam turbine,and the whole axis model of the high-pressure cylinder was established.The first eight steam flow excitation forces were coupled to the rotor,and the Riccati transfer matrix method was used to solve the influence of sealed steam flow excitation forces on the dynamic characteristics of the anisotropic rotor under different loads.The results show that increasing the seal can increase the natural speed of the rotor and restrain the vibration amplitude of the rotor.When the rotor eccentricity increases from 0.025 mm to 0.2 mm and the seal clearance increases from 0.5 mm to 0.8 mm,the first order x-z and y-z plane projection amplitude of the rotor increases,the first order natural speed decreases by 0.65% and 0.85%,the logarithmic decay rate decreases by 4% and 3.8%,respectively,and the rotor stability decreases.The increase of seal tooth thickness is beneficial to reduce the projection amplitude of the first order vertical plane of the rotor,and when the tooth thickness increases from 0.4 mm to 0.6 mm,the first order natural speed increases by 0.85%,and the logarithmic decay rate increases by 0.27%.