Design Characteristics of an Aerodynamic Foil Bearing With Adaptable Bore Clearance

Aerodynamic foil bearings are suitable to support light, high-speed rotors under extreme operating conditions such as very low or very high temperatures, e.g. in cooling turbines, small gas turbines or exhaust gas turbochargers. The required bearing load capacity is generated by an aerodynamic pressure build-up in the corresponding lubrication gap. Due to the high dependence of the bearing performance on the bore geometry, the rotordynamic behavior (e.g. bearing stability) and static properties (e.g. load capacity) as a function of radial clearance and hydrodynamic preload are one of the main points of interest in recent studies. The outcome of both the experimental and the numerical investigations show the advantages and disadvantages of the various configurations of the bearing bore in different operating conditions. These observations lead to the basic idea of an adaptive air foil bearing (AAFB) in which, depending on the operating conditions, the bearing bore contour is changed by means of piezoelectric actuators applied to the compliant supporting shell. Similar to other shape morphing approaches, optimization with regard to various components of the mechanism is the next step in the design process after targeting the design pattern. This paper concentrates on an AAFB as an efficient approach to actively shape the contour of the bore clearance in a 3-pad bearing. Numerous FEM analyses of a functional model for an AAFB in addition to the experimental efforts reveal the main concerns of the design. Finally, the result of this study is a working graph for the AAFB under various loading conditions while operating with different input voltages of the actuators.