Experimental Analyses of a First Generation Foil Bearing: Startup Torque and Dynamic Coefficients

Abstract

This paper presents the results of the experimental analysis of static and dynamic characteristics of a generation I foil bearing of 38.1 mm diameter and L/D = 1. The test rig is of floating bearing type, the rigid shaft being mounted on ceramic ball bearings and driven up to 40 krpm. Two different casings are used for startup and for measurement of dynamic coefficients. In its first configuration, the test rig is designed to measure the startup torque. The foil bearing casing is made of two rings separated by a needle bearing to enable an almost torque free rotation between the foil bearing and the static load. The basic results are the startup torque and the liff-off speed. In its .second configuration, a different casing is used to measure the impedances of the foil bearing. Misalignment is a problem that is minimized by using three flexible stingers connecting the foil bearing casing to the base plate of the test rig. The test rig enables the application of a static load and of the dynamic excitation on the joumal bearing casing and can measure displacements, forces, and accelerations. Working conditions consisted of static loads comprised between 10 N and 50 N and rotation frequencies ranging from 260 Hz to 590 Hz. Excitation frequencies comprised between 100 Hz and 600 Hz are applied by two orthogonally mounted shakers for each working condition. Stiffness and damping coefficients are identifled from the complex impedances and enable the calculation of natural frequencies. The experimental results show that the dynamic characteristics of the tested bearing have a weak dependence on the rotation speed but vary with the excitation frequency.

Preliminary experimental study on static loading characteristics of multi-decked protuberant foil thrust bearing

“…Another important distinction exists in respect of the loading-stiffness characteristics. For the bump foil structure, stiffness versus load relation is nonlinear in lightly loaded region and trends to be asymptotically stable in heavier loaded region (Ku and Heshmat, 1993;Rudloff, et al, 2011). For this multi-decked structure with 0.05 mm thick protuberant foils, bearing stiffness is almost linear in lightly loaded region and highly nonlinear in heavier loaded range.…”

“…Le Lez studied the static characterization of a bump type foil bearing and figured out that loading profile affected area of hysteresis plots by increasing or decreasing the stick or slip phases (Le Lez, et al, 2007). Besides, the nonlinearity in stiffness is imperiously necessary in the development of a clear design procedure (Rudloff, et al, 2011).…”

Numerical and experimental study on the dynamic characteristics of the foil journal bearing with double-layer protuberant support

“…According to predicted stiffness and damping factors, the natural frequency can be estimated by using a simple rotor-bearing system with a rotor only weight considered and two journal bearings support (Rudloff, 2011). When placing the origin of coordinates at the equilibrium position of the rotor, the dynamic equation for the simple rotor-bearing system can be written as: …”

A Metal Mesh Foil Bearing and a Bump-Type Foil Bearing: Comparison of Performance for Two Similar Size Gas Bearings

“…In some instances, cross-coupled stiffness coefficients are reported as significant [23]. In addition, the effects of excitation frequency and amplitude of dynamic load on the dynamic force coefficients are a recent consideration, as shown by Rudloff et al [24] and San Andrés and Chirathadam [8] for BFBs and MMFBs, respectively. In Ref.…”