Numerical analyzes and experimental investigations on the fully-coupled thermo-elasto-gasdynamic behavior of air foil journal bearings

Abstract

Air foil journal bearings are an important component in high-speed, oil-free turbomachinery applications. In order to optimize the performance of rotor systems supported by air foil journal bearings, detailed numerical models are needed. In this paper, a fully-coupled thermo-elasto-gasdynamic bearing model is presented. Using this model, the thermo-elasto-gasdynamic behavior of a mechanically preloaded three-pad air foil journal bearing is investigated numerically. Furthermore, experiments are accomplished in order to validate the results obtained with the numerical model. The 3D thermo-elasto-gasdynamic bearing model comprises the description of bump and top foil deflection and the calculation of the pressure and temperature distribution in the air film as well as the temperature distributions in the surrounding structure, namely in the rotor, in the bearing sleeve and in the top and bump foil. The bump and top foil deflection are described by a nonlinear beamshell theory according to Reissner. The model accounts for the contact between the bump and the top foil and between the bump foil and the bearing sleeve. The pressure distribution is calculated by solving the generalized Reynolds equation according to Dowson. Temperature distributions in the air film and in the surrounding structure are obtained from the 3D energy equation and appropriate heat equations. In order to reduce the computational effort of the thermo-elasto-gasdynamic problem, the 3D energy equation and the generalized Reynolds equation are reduced by an averaging approach. The governing equations are solved by a finite element method.