Experimental and numerical evaluation of the damping properties of a foil bearing structure taking into account the static and kinetic dry friction

Abstract

Over the past decades, experimental and theoretical studies on gas foil bearings have been conducted extensively. The essence of the operation of these bearings lies in the use of a unique underlying support mechanism, whose properties adapt to current operating conditions. The static and dynamic characteristics of the foil bearing structure depend not only on the geometry of the supporting structure but also on foil material, surface topology, the velocity of contact surfaces, load, etc. While the concept of stiffness is more intuitive and well described in the literature, the evaluation of the damping in foil bearings is not as obvious. The goal of this paper is to improve the understanding of the damping mechanism of the bump-type foil bearing structure under dynamic loads. At the beginning of the paper, the experimental studies of the foil bearing structure in a wide frequency range are discussed. Then, the experimental conditions were reproduced using an advanced numerical model that took into account the geometry of the top and bump foil, contact phenomena and dry friction. A new solution, unprecedented in the existing literature, is the inclusion of static and kinetic friction in the numerical model of the foil bearing structure. The developed numerical model made it possible to determine the system characteristics, including the evaluation of stiffness and damping. An important contribution of this work is the comparison of the results of calculations obtained with the use of an advanced numerical model with the results of experimental research. The paper gives clear guidelines for the experimental and numerical determination of dynamic characteristics for the bump-type foil bearing structure. The presented results of the experimental research can also be used to verify other numerical models.

A comparison of modal analyses of foil-air bearing rotor systems using two alternative linearisation methods

“…Simulations from the bilinear model used in the present paper were shown in [18] to be in close agreement with those from the more advanced model of [14]; nonetheless, it may be worth considering a 2-dimensional variation approach for the foil deflection in applications involving axially divided bump foils supporting a single top foil (e.g. [22]).…”

Performance of textured foil journal bearing considering the influence of relative texture depth

“…Thus, GFBs supported by novel foil structures, such as three-pad structure, 4 bump-type shim foil, 5 inhomogeneous bump foil, 6 etc, were presented. Meanwhile, much literature was trying to take account of the nonlinear characteristics, such as kinetic dry friction, 7 etc. But computational costs are also increasing in pace with the complexity of the model.…”

Experimental Characterization of a Foil Journal Bearing Structure with an Anti-Friction Polymer Coating

“…The inner side of the top foil, which is in contact with the journal, has a wear-resistant anti-friction coating (Figure 3b) made of a specially selected polymer (polytetrafluoroethylene-based material). The selected coating material has the trade designation AS20 and is characterized by a low coefficient of friction (the static friction coefficient is 0.1, and the kinetic friction coefficient is 0.04 [46]), high abrasion resistance and a maximum operating temperature of 280 • C. The thickness of the protective coating on the top foil is between 10 to 15 µm. This coating is necessary to protect the top foil during run-ups and run-downs.…”

“…coefficient of friction (the static friction coefficient is 0.1, and the kinetic friction coefficient is 0.04 [46]), high abrasion resistance and a maximum operating temperature of 280 °C. The thickness of the protective coating on the top foil is between 10 to 15 µ m. This coating is necessary to protect the top foil during run-ups and run-downs.…”

“…In a mechanical system with multiple points of linear or surface contact between parts, friction has a significant effect on energy dissipation and vibration damping [45]. This is why advanced friction models, which, for example, take into account changes in the coefficient of friction versus the sliding speed, are increasingly used to describe these phenomena [46]. For most solid materials, the static friction coefficient is greater than the kinetic friction coefficient.…”