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The Mechanism Analysis and Experimentation of Seal Gas Exciting in Ultra-supercritical Steam Turbine

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Tutor: ChenYuShu
School: Harbin Institute of Technology
Course: General and Fundamental Mechanics
Keywords: rotor-seal system,Comutational Fluid Dynamics,singularity theory,1subharmonic re
CLC: TM311
Type: PhD thesis
Year:  2012
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Abstract:
With development of ultra-supercritical steam technology, the parameters andthe load of steam turbine unit have been continuously improved, and gas exctingforce is increasingly prominent, which influences the stablility of the steam turbineseriously. Since the flow flied of the steam turbine are complex and the gas exctingforce on the rotor has much nonlinear factors, it is difficult to reseach the gasexciting force of the turbine. The paper is supported by the National Natural Sciencefoundation of key projects,¡°some nonlinear dynamics problems ofultra-supercritical turbine generator rotor system¡±. The effect of the gas flow in theseals for the rotor is researched by Comutational Fluid Dynamics (CFD) technologyand the experimemtal study of the rotor-seal system. By nonlinear dynamicsmethods, the mechnanism of the gas exciting force in the seal for the steam tubineunite are studied. The main content and conclusions of the paper are as follows:The two-dimension model and three-dimension model of the seals on the shaftare established. Based on the calculation of interior flow field of the seals using theCFD method, the charateristics of the seals are analyzed. And then, the paperresearches the effect of relative eccentricity, rotating speed of the rotor and thepressure ratio of the seal on the gas exciting force, which shows the nonlinearrelationship between the gas exciting force and the paramters. Lastly the empiricalparameters and experimental parameters of the Muszynska gas exciting force modelare identified to solve the problem that the parameters of the model are difficult todetermine. The identified coefficients of the shaft seal model on the steam turbineunit are suitalbe. The results mentiond above provide the basis for the nonlineardynamic analysis of the rotor-seal system.The power series model of the rotor-seal system of the ultra-supercritical steamturbine are obtained by Taylor expansion. According to Hopf bifurcation theory andstability theory, the paper researches the mechanism of the instability of therotor-seal autonomous system of the ultra-supercritical steam turbine on theequilibrium position. The results shows that system has the Hopf bifurcationphenomenon at the sloved theshold speed, and have the periodic orbit after the Hopfbifurcation. The multiple scale method are used to obtain the bifurcation equationsof the rotor-seal non-autonomous system of the ultra-supercritical steam turbine, forstudying the effects of the rotor¡¯s imbalance excitation on the nonlinear dynamiccharacteristic of the system, in the1:2subharmonic resonance case. Through thesingularity analysis of the1:2subharmonic resonance bifurcation equations, the paper studied engineering unfolding problems of the rotor-seal system. Thetransition sets and the local bifurcations diagrams of the system parameter space areobtained. The results show that system has the supercritical Hopf bifurcation andsubcritical Hopf bifurcation in the different parameters regions. Lastly, Floquetmultiplier is applied to the study on the stabilities and dynamic behaviors of theperiodic solutions of the systems by shooting method.According to the real solution conditions of the bifurcation equations in the1:1main resonance,1:2subharmonic resonance and1:3subharmonic resonance, theArnold tongue are constructed to study the global bifurcation of the system by theanalytical method. Then the paper studies the dynamic characteristics of the systemin the Arnold tongues overlap and non-overlap. The results show that when thesystem parameters are in the Arnold tongues overlap region, the system appearmulti-times cycle motion and chaotic motion for the coexistence of the resonancesolutions. And the chaotic motion is confirmed by the largest Lyapunov exponent.Finally, the dynamic testing rig of the rotor-seal system are designed and builtin the Harbin Institute of Technology for further studying the effect of the gasexcitation on the rotor-seal system. According to the current condition of experiment,the structure parameters of the rig are confirmed by CFD calculation and theoreticalanalysis. The seal structure simulates the current structure of the steam turbines ofHarbin steam turbine factory, and independent seal facility with adjustable clearanceis designed to achieve the dynamic tests of the system with the different clearancesin the same rig. By using effect coefficient method, the dynamic balance of the rotorreaches a good level and the rotor can work at high rotating speed. The vibrationtests of the rotor are done when the input pressure is zero and different values, tostudy the influence of the gas excitation.
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