NDLI: Heavily Loaded Gas Foil Bearings: A Model Anchored to Test Data

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Kim, Tae Ho Andre´s, Luis San
Copyright Year	2005
Abstract	Widespread usage of gas foil bearings (FBs) into micro turbomachinery to midsize gas turbine engines requires accurate performance predictions anchored to reliable test data. The paper presents a simple yet accurate model predicting the static and dynamic force characteristics of gas FBs. The analysis couples the Reynolds equation for a thin gas film to a simple elastic foundation model for the top foil and bump strip layer. An exact flow advection model is adopted to solve the partial differential equations for the zeroth- and first- order pressure fields that render the FB load capacity and frequency dependent force coefficients. As the static load imposed on the foil bearing increases, predictions show the journal center displaces to eccentricities exceeding the bearing nominal clearance. A nearly constant FB static stiffness, independent of journal speed, is estimated for operation with large loads; and approaching closely the structural stiffness derived from contact operation at null rotor speed. Predicted minimum film thickness and journal attitude angle demonstrate good agreement with archival test data for a first-generation gas FB. The bump-foil strip structural loss factor, exemplifying a dry-friction dissipation mechanism, aids to largely enhance the bearing direct damping force coefficients. At high loads, the bump-foil structure influences most the stiffness and damping coefficients. The FB whirl frequency ratio (WFR) is examined to ensure its dynamically stable operation. The predictions demonstrate that FBs have greatly different static and dynamic force characteristics when operating at journal eccentricities in excess of the bearing clearance from those obtained for operation at low loads, i.e. small journal eccentricities.
Sponsorship	International Gas Turbine Institute
Starting Page	763
Ending Page	771
Page Count	9
File Format	PDF
ISBN	0791847276
DOI	10.1115/GT2005-68486
e-ISBN	0791837548
Volume Number	Volume 4: Turbo Expo 2005
Conference Proceedings	ASME Turbo Expo 2005: Power for Land, Sea, and Air
Language	English
Publisher Date	2005-06-06
Publisher Place	Reno, Nevada, USA
Access Restriction	Subscribed
Subject Keyword	Structural force coefficients Gas foil bearing Dynamic force coefficients Structural loss factor Foil bearings
Content Type	Text
Resource Type	Article

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