STRUCTURAL STIFFNESS AND COULOMB DAMPING IN COMPLIANT FOIL JOURNAL BEARINGS - THEORETICAL CONSIDERATIONS

Compliant foil bearings operate on either gas or liquid, which makes t hem very attractive for use in extreme environments such as in high-te mperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing , which is time-consuming and expensive. In this paper, the authors pr esent a theoretical model to predict the structural stiffness and damp ing coefficients of the bump foil strip in a journal bearing or damper . Stiffness is calculated based on the perturbation of the journal cen ter with respect to its static equilibrium position. The equivalent vi scous damping coefficients are determined based on the area of a close d hysteresis loop of the journal center motion. The authors found, the oretically, that the energy dissipated from this loop was mostly contr ibuted by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonlinear behavior of the bump foil s trips were examined. With the introduction of this enhanced model, the analytical tools are now available for the design of compliant foil b earings.