Air foil bearings offer several advantages over oil-lubricated bearings in highspeed micro-turbomachinery. With no contact between the rotor and bearings, the air foilbearings have higher service life and consequently lesser standstills between operations.However, the foil bearings have reliability issues that come from dry rubbing duringstart-up/shutdown and limited heat dissipation capability. Regardless of lubricatingmedia, the hydrodynamic pressure generated provides only load support but nodissipation of parasitic energy generated by viscous drag and the heat conducted fromother parts of the machine through the rotor.The present study is a continuation of the work on hybrid air foil bearings(HAFB) developed by Kim and Park, where they present a new concept of air foilbearing combining hydrodynamic air foil bearing with hydrostatic lift. Theirexperimental studies show that HAFB has superior performance compared to itshydrodynamic counterpart in load capacity and cooling performance.In this article, the bearing stiffness and damping coefficients of HAFB are calculatedusing a linear perturbation method developed for HAFB. The study focuses on circularHAFB with a single continuous top foil supported by bump foil. The research also includes a parametric study which outlines the dependence of the stiffness and dampingcoefficients on various design parameters like supply pressure ( P s ), feed parameter ( ? s ), excitation frequency (v), and bearing number (?).Furthermore the present research also includes experimental investigation ofHAFB with bump foil as compliant structure. In the first phase of the experimentalresearch a high speed test facility was designed and fabricated. The facility has thecapability of running up to 90,000 RPM and has an electric motor drive. This articlegives detailed description of this test rig and also includes data acquired during thecommissioning phase of the test rig. The test rig was then used to measure the loadcapacity of HAFB.
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