A Semi-Analytical Model of Shape-Control in an Adaptive Air Foil Bearing

The aerodynamic foil bearing is a special type of air bearing in which the flexible foil structure between rotor and rigid housing supports the rotor bearing system with a greater robustness against thermal distortion and production misalignments. In such bearings, the generation of an aerodynamic pressure in the lubricating film after reaching the lift-off speed prevents the solid contact between rotor and foil structure. Since many static and dynamic properties of air foil bearings strongly depend on the inner contour of the bearing, the idea of an adaptive air foil bearing (AAFB) is developed to optimize the bearing’s performance at different operating points. This paper concentrates on a semi-analytical model based on plate theory using Ritz method for simulating the static shape control of piezoelectrically actuatable supporting segments for an AAFB under different loading conditions. The elastic suspension of the supporting segments and symmetries of the bearing are considered in the modeling. After validation by means of FEM analyses and experimental tests the influence of geometry and material is examined in a parametric study. Later on, the model is used for parameter optimization in order to achieve the most effective shape morphing.