A New Structural Bump Foil Model With Application From Start-Up to Full Operating Conditions

Abstract

This paper presents a new structural bump foil model that can handle all operating conditions from start-up to full speed. The model is based on a nonlinear contact algorithm with friction and gaps. The top foil is modeled as a curved beam while bump foil uses a coupled truss model. The model considers the gaps between the bump foil and the bearing casing, between the bump foil and the top foil and between the rotor and the top foil. Thus, any numerical interference between the rotor and the top foil is avoided. A mixed lubrication model is used for the thin film pressures. Following this algorithm, contact pressures appear if the film thickness is less than three times the equivalent roughness of the rotor and of the top foil. Fluid pressures are calculated from numerical solutions of Reynolds equation while contact pressures, if present, are calculated with the model of Greenwood and Williamson. The model is validated by comparisons with the experimental results obtained for start-up operating conditions of a first-generation foil bearing of 38.1 mm diameter with static loads of 10–50 N. Theoretical predictions of the start-up torque and takeoff speed compare well with experimental results. It is also shown how manufacturing bump height errors can explain the differences between theoretical and experimental predictions. Further validations are presented for the same bearing operating at high speeds (30, 45, and 55 krpm) and heavy static loads (up to 200 N). The calculated minimum film thickness and attitude angle are compared with experimental data from the literature.

Influence of Aerodynamic Preloads and Clearance on the Dynamic Performance and Stability Characteristic of the Bump-Type Foil Air Bearing

“…The validation of the foil model in Figure 2, based on the displacement results of a cantilever beam in a uniform and a increasing load case (LC) by Le Lez et al [17], shows a good agreement. The present NDOF bump-foil model, established by Le Lez et al [17], is further extended by Arghir et al [18,19], which is not the scope of the present study.…”

Analysis of misalignment characteristics for textured foil journal bearing based on multigrid method

“…Previous studies [10] suggested that the bearings' static characteristic results based on Heshmat's linear spring model [24] were instructive to the research based on the N DOF model [32,33]. Hence, these two analytical foil models were adopted in this paper to obtain the foil structure's local deformation u in equation (6), and the details are shown in figure 1(e).…”

An efficient three-dimensional foil structure model for bump-type gas foil bearings considering friction

“…Recently, Arghir and Benchekroun [25] further developed the foil model introduced in [17] by modeling the closeloose contacts between the top foil and the bump foil to consider possible gaps and manufacturing errors in the foil structure. This foil model was then coupled with the gas film model to determine all operating conditions of GFBs from start-up to full speed [26]. However, all of the above models are planar models, thus they cannot reflect the three-dimensional (3D) characteristics of a bump foil.…”