Evaluation of a Gas-Lubricated Foil Bearing for Control of Gas Turbine Engine Rotor Critical Speeds

The effectiveness of gas-lubricated foil bearings for use in reducing small gas turbine rotor vibration levels has been evaluated through application of the Hydresil foil bearing to a power turbine shaft simulator, operating in flexibly-mounted ball bearings without support damping. A series of tests showed the three-pad Hydresil bearing to be superior to the 360-degree and two-pad configurations for the journal size and speeds tested. In-place multiplane-multispeed rotor balancing was used to establish a “baseline” rotor which had the first (bending) shaft-bearing system critical speed and a pedestal resonance suppressed, and a distinct vibration peak at the second (bending) critical speed. The test Hyresil proved to be capable of increasing the second critical speed by over 50%, as evidenced by a shift of the resonance peak to a speed above the normal operating speed range of the power turbine shaft.