Research On Rotor-bearings System Nonlinear Dynamics Behaviors, Fluid-solid Interaction And Its Frequency Modulations

The emphasis of this dissertation is on the issues of nonlinear dynamics behaviors, fluid-solid interaction and its frequency modulation of bearing-rotor system. The research aims at the deeper understanding of the lubricant-journal interaction mechanism, the correlation among lubricant flow, journal dynamics and bearing load. Based on the nonlinear dynamics behaviors in bearing-rotor system, the methodology of frequency modulation to enhance the stability of bearing-rotor system is presented.According to the analytical solution of Reynolds equations of journal bearings and the expression of nonlinear dynamic oil-film force, the characteristics of low-frequency whirling in journal bearing is analyzed. At the same time, the applicability of the analytical solution of Reynolds equations for gas lubricated bearing is discussed based on incompressible flow assumption, which lies theoretical foundation for the frequency modulation experiments of gas bearings-rotor system. With the definitions of the mechanism of fluid-solid interaction and frequency modulation in bearing-rotor system, the concept of "fluid-solid interaction and frequency modulation" is further expatiated. In addition, the engineering stability criterion for bearing-rotor system is presented based on bearing-rotor system load balance equations.The experiment of hydrostatic hybrid gas bearing-rotor system is performed. From the view point of nonlinear dynamics, the characteristics of gas whirling, whipping and instability is researched. The phenomenon of gas whipping caused by the coupling between system natural frequency and gas whirling frequency, and the rub-impact cause by gas instability is observed. The "bound ness" of chaos and the routine to chaos after gas instability are validated. With the principles of fluid-solid interaction and frequency modulation, some measurements are summarized: adjust the coupling relation between gas whirling frequency and system natural frequency in order to keep design operation rotating speed away from gas instability speed range to ensure considerable safety margin; with the engineering stability criterion, amplitude should be effectively controlled and the rotating speed range at which chaos instability occurs should be narrowed. The effective restrain of gas whirling energy accumulation is able to avoid gas instability and to enhance system stability.The experiment of gas bearings-rotor system fluid-solid interaction and frequency modulation is accomplished. The static and dynamic modulation experiments indicate that: the adjustment of bearing static supply gas pressure changes the system natural frequency and bearing stiffness so as to change the coupling relationship between gas whirling frequency and system natural frequency, which validates the controllability of low-frequency gas whirling under the condition of frequency modulation. The low-frequency whirling energy capture caused gas whipping is an adverse effect on the stability of bearing-rotor system. In the speed range of gas instability, the appropriate bearing gas supply pressure and shaft work input is able to restrain the energy accumulation of low-frequency whirling to avoid the gas instability caused by the low-frequency energy capture. The phenomenon of "double low-frequency" caused by the bearing geometric difference is also studied, as well as the relevant application of frequency modulation in "double low-frequency". In conclusion, the regularity of fluid-solid interaction in bearing-rotor system is summarized and the validity and practicability of frequency modulation is further validated.