Performance Characteristics of Metal Mesh Foil Bearings: Predictions Versus Measurements

Abstract

Proven lowcost gas bearing technologies are sought to enable more compact rotating machinery products with extended maintenance intervals. The paper presents an analysis for predicting the static and dynamic forced performance characteristics of metal mesh foil bearings (MMFBs) which comprise a top foil supported on a layer of metal mesh of a certain compactness. The analysis couples a finite element model of the top foil and underspring support with the gas film Reynolds equation. A comparison of the predictions against laboratory measurements with two bearings aims to validate the analysis. The predicted drag friction factor in one bearing (L = D = 28.00 mm) during full film operation is just f ∼ 0.03 at ∼50,000 rpm, in good agreement with measurements at increasing applied loads. The predictions further elucidate the effect of the applied load and rotor speed on the bearing minimum film thickness, journal eccentricity, and attitude angle. For a second bearing (L = 38.0 mm, D = 36.5 mm), predicted bearing force coefficients show magnitudes comparable with the measurements, with less than a 20% difference, in the 250–350 Hz excitation frequency range. While the predicted direct stiffness coefficients are rather constant, the experimental force coefficients increase with frequency (maximum 400 Hz), due mainly to the increasing amplitudes of dynamic force applied to excite the bearing with a set amplitude of motion. The analysis underpredicts the direct damping coefficients at high frequencies (>300 Hz). The crosscoupled stiffness and damping coefficients are typically lower (<40%) than the direct ones. The bearings operated stably at all speeds without any subsynchronous whirl. The reasonable agreement of the predictions with the available test data promote the better design and further development of MMFB supported rotating machinery.