Operating characteristics of the bump foil journal bearings with top foil bending phenomenon and correlation among bump foils

In many previous studies, the experimental results show the ripple traces of the post-test top foil due to the top foil deflection differences between the areas touched with and without bump foil. This phenomenon represents clearly the behaviour of the top foil motion. Therefore the top foil deflecting appearance should be taken into consideration for more reliable estimation of the bump foil bearing behaviour. However inherent top foil bending effect was ignored under assumption to the rigid body able to act only vertically. In this paper, a numerical analysis and its experimental investigation were studied with the intention to abstract the static and dynamic characteristics of the bump foil bearing considering the top foil bending effect and correlation among bumps. The bump and top foil inserted between the journal and the bearing housing have each mechanism as a shock absorber and journal supporter, and each mechanism was analysed using numerical method, respectively. In the case of the top foil, the deflection of that and Coulomb damping generated by relative friction was taken into consideration theoretically. In addition bump foil analysis was executed to be assumed to have a structure that flexible bumps with corrugated shape are connected with each other. This analysis verifies that the stiffness at the fixed end where the friction forces between the bearing housing and bump foil superpose is more than that at the free end. Using this structural analysis, the overall analysis of the bump foil bearing was executed through coupling process. In parallel, the experimental process was carried into execution with the bump foil bearing that L/D is 1. The rotating speed was from 10,000 up to 30,000 rpm and the load was 50 N. By comparing the analysis with the experimental results, the effects of the structural characteristics of bump foil were presented.