Study On Dynamics Of A Rotor-Bearing-Seal System

As rotating machinery become large-capacity, the stabilization and dynamics of rotating rotor were influenced by the increasing in coupled interaction between the fluid and the rotor. Therefore in the present study the dynamic characteristics of the rotor-bearing-seal system. And the present study is involved in the mathematical modeling of seal force and dynamics analysis of a rotor-bearing-seal system, which combines the theoretical modeling, the numerical simulation with experimental investation. The project is supported in part by National Hi-Tech Research and Development Program (863) of China (approved No. 2002AA52613-8), by National Natural Science Foundation of China (approved No.10572087). The research content is given in detail as follows:From the viewpoint of theoretical analysis and engineering application, the background and significance of the present study are elucidated. Status and development of research on the nonlinear dynamics of a rotor and seal force are introduced.Supported by National Hi-Tech Research and Development Program (863) of China, the laboratory setup of the rotor-bearing-seal experimental device, which scale the seal structure and journal bearings. The experimental device can simulate the pressure ratio, ratating speed and unsteady and steady pressure. Furthermore, the signals of staic pressure, fluctuating pressure, rotating speed and rotor displacements can be acquired simultaneously. As a result the experimental device provides the experimental basis for investigating the coupled interaction between the seal and the rotor.Tow-control-volume model has been detailedly expounded in computing dynamic characteristics for the see-through labyrinth seal. In this paper, the height of the seal is introduced in the improved two-control-volume method. And the result of the present method is in good agreement with the experimental data, which had been conducted by Childs, so it is feasible using this method to predict the dynamic characteristics of see-through labyrinth seal. In addition, the influences of the system first-order critical speed and its logarithmic decrement have also been probed into. With increase in inlet preswirl velocity, the cross-coupled stiffness increases. It also shows that the first critical speed of the rotor decreases by the seal force. And the first critical speed decreases rapidly in inlet pressure. Moreover, the research shows that the inlet preswirl velocity has a greate effect on the stability of the rotor with seals. The stability of rotor obtained from the positive inlet preswirl velocity is more unsafe than that from the opposite directions with same absolute values. This implies that neglecting the coupled fluid-solid effect will result in unsafe prediction of the stability of the rotor. The results of current method are in agreement with the one from the experimental. Accordingly, the improved two-control-volume model was validatedThe complex experimental rotor system is simplified as the Jeffcot rotor. Based on the short bearing theory, the nonlinear oil-film force mode is given. And a simply model of nonlinear seal force based on the results of a series of experiments was proposed by Muszynska. Then the dynamic model of the nonlinear rotor-bearing-seal system was set up. The simulated result tends to agree with the experimental data. As a result, the study may contribute to a further understanding of the non-linear dynamics of such a rotor-bearing-seal coupled system. It is indicated that the dynamic behavior of the rotor-bearing-seal system depends on the rotation speed, rotor eccentricity, seal clearance and seal pressure of the rotor-bearing-seal system. Therefore, by changing the values of these factors, the bifurcation of the coupled system is analyzed. Then the dynamic behavior of the rotor center are analyzed by the system state trajectory, Poincare maps, frequency spectra, bifurcation diagrams and the curves of maximal Lyapunov exponent. From the results of the numerical simulation, it is found that there are periodic motion, doubling-periodic motion, multi-periodic motion and approximate-periodic motion in the coupled system. Finite element method is proposed to estabilish a dynamic mode of rotor-bearing-seal system. And the results of the present method are in good agreement with the experimental. Then study on nonlinear dynamics of a rotor-bearing-seal system by the bifurcation diagram, state trajectories, frequency spectra and waterfall. From the numerical simulation, it is found that the simulated results of the current calculation are more accurate according to the experimental result than that of the Jeffcott rotor.