| As the large-scale rotational machinery,the vibration of steam turbine rotor seriously affects the safety of operation.With the development of high-parameters and large-capacity steam turbine,the steam flow excited vibration in seal has become one of the main factors for rotor instability.Especially the ultra-supercritical steam turbine,the steam flow excited vibration in seal is prominent.Based on the real situation of whirling rotor,a whirling rotor model was established and the mechanism of steam flow excited vibration was analyzed.The dynamic characteristics of seal,the rotor motion and the response of the high-pressure cylinder rotor were analyzed by the combination of the numerical simulation and theoretical algorithm.The mechanism,process and characteristics of the rotor instability induced by seal steam flow excited vibration were presented.The influence of seal steam flow excited vibration on rotor stability was analyzed,which provided a theoretical basis and technical guarantee for the design and stable operation of the unit.Firstly,the User-Defined Functions(UDF)including DEFINE?CG?MOTION and DEFINE?PROFILE control macros were used to compile the whirling and rotational equations of the rotor,which solved the problem that the current rotor whirling model is over assumed.The mixing loss of leakage steam and main steam in turbine cascade and the entropy-increasing rate in high loss region influenced by seal clearance were analyzed.On this basis,the characteristics of circumferential and axial pressure fluctuation in seal flow field were studied.The influence of uneven clearance on the pressure distribution was analyzed.The main regions and frequency components of pressure fluctuation inducing seal steam flow excited vibration were studied.The internal relationship between seal steam flow excited vibration and flow field characteristics was obtained.When the leakage steam of seal flow through the rotor cascade,the influence range of leakage steam moves to the middle of blade along the radial direction because of the passage vortex entrainment.When the rotor whirls,the pressure fluctuation at seal inlet is more severe and the sharp increase of pressure amplitude in high pressure region is the main reason for the unsteady and significant variation of seal steam flow exciting forces.Secondly,the nonlinear seal steam flow exciting force is solved by the multi-frequency whirling equation and the small disturbance theory.The phase-frequency characteristics of the force and displacement were used to reveal the work process of seal steam flow excited vibration on rotor.The seal dynamic coefficients in frequency domain were solved by MATLAB Fast Fourier Transform(FFT).The boundary parameters of 100%,75%,40% and 30% turbine heat –acceptance(THA)were set to analyze the variation of seal steam flow excited vibration in the process of increasing load.Based on the fluid-structure coupling model of Workbench,the heat load and centrifugal effect were coupled to the rotor surface to study these influences on the seal dynamic characteristics.Based on the relative rotational model,the whirling equations of stator and rotor were established respectively to develop the conical multi-frequency whirling motion of the large diameter rotor.And the seal dynamic characteristics in conical whirling motion were obtained.Taking the sealing structure parameters as the influence factors,a quaternion quadratic orthogonal test was established to analyze the influence of the main factors on seal dynamic characteristics.The optimized sealing structure with better dynamic stability was proposed.When the seal structure parameter ratio is tooth width: clearance: cavity depth: pitch =2.3:1:18:25,the dynamic instability range of seal disappears.Thirdly,the motion equation of the single-disk turbine rotor was established according to the single-disk Jeffcott rotor model.With the consideration of the rotational velocity,whirling frequency and rotor eccentricity,the polynomial equation of nonlinear steam flow exciting force was fitted and coupled to the differential equation of rotor motion.The Runge-Kutta method in MATLAB was used to solve the motion of rotor.On this basis,the steam flow exciting forces of different seal structures were fitted to analyze the influence of seal structure on the motion of rotor.The stability of rotor motion under steam flow excited vibration was analyzed via the axis trajectory diagram and Lyapunov exponent.According to the periodic characteristics of the rotor motion and the fluctuation of displacement amplitude,the load region and the main frequency component of rotor instability were determined.The nonlinear steam flow exciting force can cause the whirling center of rotor shifting and nonlinear motion,the vibration frequency appears1/2 frequency,the first critical speed frequency(about 2/3 frequency)and low frequency below1/2 frequency.With the increasing of unit load,the chaotic region of rotor motion becomes wider,and the maximum Lyapunov exponent is greater than zero,which promotes the rotor instability.Finally,the lumped parameter method was used to the modeling of 1000 MW high-pressure cylinder rotor.And a dynamic equation of the rotor with anisotropic support was established.The natural frequency,principal mode and trajectory of each node under the design condition were calculated by Riccati transfer matrix method,the results were verified to ensure the accuracy of calculation.On this basis,the effect of seal steam flow excited vibration simplified as the external bearing support was applied to the shaft system.So the influence of the steam flow excited vibration on the response characteristics of the shaft system was analyzed.The influence of seal steam flow excited vibration on the rotor critical speed is small,but the displacement amplitude and stability of the first mode vibration mode have the great variation.With the influence of the steam flow excited vibration,the first mode amplitude of the initial point is increased. |
PDF Full Text Request