On Nonlinear Rotor Dynamic Effects of Aerodynamic Bearings With Simple Flexible Rotors

Abstract

The last decades have experienced a growing enhancement of aeronautical oil free turbomachinery. The classical linear approach of rotor dynamics commonly uses stiffness and damping coefficients to model journal bearings. In the present study, a nonlinear time dependant calculation is used for the dynamic simulation of a rotor mounted with aerodynamic (gas) bearings. A comparison between the two approaches indicates that the dynamic behavior of such bearings can be nonlinear in operating ranges where the rotor eccentricity reaches high values. In that case, the linear approach may lead to incorrect results and the nonlinear approach should be performed for better rotor dynamic prediction. A numerical procedure which analyzes the dynamic behavior of simple flexible rotors taking into account the nonlinear (transient regime) characteristics of aerodynamic bearings is presented. A simple example highlights the needs of nonlinear simulations in order to predict dynamic performance in oil-free turbomachinery.