Abstract: The nonlinear stiffness model of single bump foil is derived from foil bearing structural stiffness tests. By using finite difference method, the gas Reynolds equation is solved coupled with film thickness and single bump foil stiffness equation. The effects of bump foil nonlinear stiffness on foil bearing static performance are studied. The numerical results of bump foil nonlinear stiffness model are compared with constant stiffness model from reference. The results indicate that single bump foil has strong nonlinear stiffness. The stiffness of bump foil at bearing load zone is much larger than that in non-load zone due to the uneven gas pressure distribution. Since the small bump foil stiffness value of nonlinear stiffness model in light load case, the journal eccentricity and gas film thickness at non-load zone of nonlinear stiffness model are much larger that the results of constant stiffness model. In addition, a new approach to analyze foil bearing static performance is summarized which is derive single bump foil nonlinear stiffness model from bearing structural stiffness experiments before numerical analysis of bearing.

Key words: bearing static performance, bump foil nonlinear stiffness model, finite difference method, bump-type gas foil bearing