Experimental determination of the rotor dynamic coefficients of a gas-lubricated foil journal bearing

This thesis describes an experimental investigation of the dynamic stiffness and damping characteristics of an air lubricated leaf-type foil journal bearing. A test bed with dynamic force and response measurement capabilities has been designed and fabricated as a part of the research effort. The test bed consists of a two inch diameter rotor which is supported on two hydrostatic air bearings. The test bearing is centered on the test rotor. The test bed has rotor speed capability of up to 30,000 rpm. Transverse static and dynamic loads of up to 100 lbs can be applied to the test bearing. Direct and cross-coupled transverse stiffness and damping coefficients for a two inch diameter by two inch long eight-leaf foil bearing are obtained using a frequency domain estimation algorithm. Foil bearing dynamic coefficient data is presented for a range of average bearing loads, rotor speeds, and whirl frequency ratios. Experimental predictions of dynamic coefficients for a plain rigid test bearing have been obtained for test bed validation purposes. These experimental results are shown to be in good agreement with corresponding theoretical predictions of rigid bearing dynamic coefficients obtained using a linearized perturbation analysis method. Simulated data has been used to investigate the effects of sensor calibration error and quantization error on the prediction of dynamic coefficients. The results of these investigations are also presented. A rotordynamic analysis is also presented and demonstrates how the dynamic coefficient data can be used to obtain a quantitative assessment of rotor/bearing system stability and frequency response characteristics. Dynamic response characteristics for rigid and compliant surface bearings are compared. The results substantiate the notion that foil bearings have enhanced dynamic performance characteristics in comparison to their rigid bearing counterparts.