Study On Vibration Of Ultra Supercritical Turbine Rotor Systems And Nonlinear Dynamics Of Several Rotor Systems With Faults

With the structural adjustment of our country's electric power industry, designing, manufacturing and developing large steam turbines such as ultra supercritical turbines is the inexorable trend to save energy, protect the environment, increase the energy-generating efficiency, and reduce the generating cost. However, by increasing parameters of the steam and reducing the seal clearance, the seal force from the interaction between the rotor and the labyrinth seal is increased. Moreover, the oil-film forces from the journal bearing exist generally. These two kinds of forces deteriorate the instable problems of ultra supercritical turbines more seriouly. By reducing the seal clearance, the possibility of rubbing faults between the rotor and the seal is enlarged. Lots of heat is generated from the rub, which can cause the permanent bending of the shaft. This bending aggravates the rubbing fault. In a practical large scale turbines, because of mass unbalance and external excitations, coupled lateral-torsional vibration of the rotor system becomes more prominent, which makes the system have complicated nonlinear characteristics and increases the instable possibility further. To solve above problems, this thesis carries out efficient study. The research content and achievements are given in detail as follows:To study the fluid-induced instability of the rotor system of large scale turbines by oil-film forces and seal forces, based on the finite element method, a software which can analyze dynamics and stability of the rotor system of large scale turbines is developed which includes the seal force and the oil-film force, etc. It can calculate mode shapes and critical speeds, and analyze the linear stability of the rotor system. Moreover, the rotor system of a home-built 1000 MW ultra supercritical steam turbine is studied using the software. The practical problem of how to analyze dynamic characteristics and judge the stability of this kind of large scale turbine rotor system is solved. The results show influence of the seal force mainly focuses on the high pressure part and interim pressure part of the turbine rotor system. The seal force decreases logarithmic decrements of the rotor system notably. This means the seal force reduces the stability of the rotor system.Vibration characteristics and stability of the rotor system subjected to both the seal force and the oil-film force are investigated experimentally. A rotor-bearing-seal experimental device with high pressure and high rotating speeds is set up for the first time domestically, which makes parameters of the device match those of practical turbine systems. Based on the experimental results, system's first critical speed and stability are got. The unstable process of the system because of the oil whirl and oil whip is analyzed in detail, and effect of the seal force on the system's stability is investigated. Meanwhile, using the software, theoretical calculation is carried out to the experimental rotor system. Theoretical results match well with experimental results, which proves the validity of the developed software. Both results show that the seal force decreases the critical speed of the rotor system and the critical speed falls with further increase of air pressure;the system becomes unstable because of oil whirl and oil whip, the seal force decreases the threshold of instability of the system, and the threshold of instability is decreased with the increase of air pressure.Then the experimental rotor system is simplified as the Jeffcott rotor. The short bearing theory is utilized to model the nonlinear oil-film forces and Muszynska nonlinear seal force is used. The nonlinear governing equations of the rotor-bearing-seal system are set up. By using numerical method, effect of system parameters such as the seal clearance and system damping, and operating parameters such as the rotor rotating speed and the input-output air pressure difference on the nonlinear dynamics and stability of the rotor-bearing-seal system are investigated Nonlinear theoretical results are compared with the ones from experiments and they match well.Theoretical investigation is carried out to the initial deflection fault of the shaft and the rubbing fault which exist universally in practical steam turbines. First, the rubbing condition of an unbalanced rotor system with initial deflection is investigated. The rubbing factor is introduced to determine whether the rub would happen or not for all rotating speeds. Rubbing speeds when rub begins to happen are calculated. An unbalanced rotor-stator rubbing model with initial permanent deflection is set up and the corresponding governing motion equation is derived by d'Alembert principle. Through the analytical method, parameters such as the mass eccentricity, the initial permanent deflection and the damping coefficient are used to analyze their effect on the rubbing factor and rubbing speed. Then a general model of an unbalanced rub-impact rotor-bearing system with initial permanent bow is set up and the corresponding governing motion equation is given. The nonlinear oil-film forces from the journal bearing and nonlinear forces from the rub are included. Through numerical calculation, system parameters such as the rotating speed and initial permanent deflection are used as control parameters to investigate their effect on nonlinear dynamics of the rotor system. Complicated motions such as periodic, quasi-periodic even chaotic vibrations are observed. Under the influence of the initial permanent deflection, different routes to and out of chaos are found and the speed when the rub happens is changed greatly.The coupled torsional-lateral model of the rotor system is set up and governing equations are derived using Lagrange approach with six degrees of freedom. Two kinds of unbalances including static unbalance and dynamic unbalance are considered in the rotor system. The gyroscopic effect and the gravity are considered. Torsional and lateral motions are also subjected to external excitations. Through numerical simulation, the developed model is used and the coupled torsional-lateral vibrations of the unbalanced rotor system under external excitations are investigated. Numerical simulation is carried out. Through numerical investigation, the characteristics of the coupling between torsional and lateral vibrations of this unbalanced rotor system under external excitations are found and discussed.