Modal Analysis of Rotor System Supported On Hydrodynamic Journal Bearing Using ANSYS Workbench

Abstract

Hydrodynamic journal bearing has wide range of applications from jet engines, compressors to turbines. These bearings are used to support heavy rotors of power plant machinery. One of the limitations of using hydrodynamic journal bearings is the possibility of instability of the rotor system due to the tangential forces developed due to the fluid flow inside the bearing. The phenomenon of instability of rotors supported on journal bearings has been simulated in this work. ANSYS Workbench software has been used for this purpose.
Modal analysis of a two disc rotor system supported on hydro dynamic journal bearings has been simulated. Variation of bearing coefficients over a spin speed range is firstly studied. Modal characteristics have then been found out as the spin speed of the rotor shaft changes. Campbell diagram has been plotted to find out he spin speed dependent natural frequencies and to determine the critical speed of the system. Various plots like stability plots (where real part of Eigen values are plotted) or the plots of modal damping factor or the logarithmic decrement can be plotted to locate the stability limit speed. Hence an easy to apply approach of modal analysis of a rotor system supported on journal bearings has been given in the work to plot the Campbell diagrams, Stability plots and in turn to find out the critical speed and stability limit speed of the system.