An Experimental Study of the Load-Orientation Sensitivity of Three-Lobe Bearings

Abstract

Static and dynamic performance test results are provided for a three-lobe bearing evaluated over the following range of radial static-load orientations (taken from the leading edge of the loaded pad): 0°, 20°, 30°, 40°, 80°, 90°, and 100°. Static and dynamic test results are evaluated to determine the sensitivity of the bearing to changes in the static load direction. The bearing has the following specifications: 100o arc angle, 0.52 preload, 70% offset, 101.74 mm minimum bore diameter, 0.116 mm radial pad clearance, and 76.3 mm axial length. The bearing is tested at 6750 rpm, 9000 rpm, 10800 rpm, and 13200 rpm, and at five different unit loads. Static measurements include hot and cold clearances, static eccentricities, and pad metal temperatures. Dynamic results include stiffness coefficients, damping coefficients, and whirl-frequency ratios (WFRs). Dynamic tests show that the three-lobe bearing is very sensitive to load orientation at low speeds and high loads. Kxx is highest for the 80°, 90°, and 100° load orientations. Kyy is highest for the 20°, 30°, and 40° load orientations. Kxy is highest for the 80°, 90°, and 100° load orientations. The magnitude of Kyx is highest for the 0° and 20° load orientations. Cxx is largest for the 80°, 90°, and 100° load orientations, and Cyy is largest for the 0°, 20°, 30°, and 40° load orientations. In terms of WFRs, it is generally dynamically advantageous to orient the static load vector for this bearing towards the leading edge of the pad. WFRs at 6750 rpm with loads of 1149 kPa, 1723 kPa, and 2298 kPa are equal to zero when the static load vector is pointed towards the leading edge of the pad and between 0.25 and 0.5 when the static load vector points towards the trailing edge of the pad. The bearing is not sensitive to load orientation at high speeds and light loads. At 13200 rpm, measured WFRs are between 0.2 and 0.6 at all loads and for all load orientations. Measured WFRs at the no-load condition are approximately 0.5 at all speeds. Static data showed that the 30° and 90° load orientations yielded slightly higher measured maximum pad-metal-temperature increases at each speed relative to the other load orientations. At the highest static-load magnitudes, the pad metal temperatures are not as dependent on load orientation. The 20°, 30°, and 40° load orientations had the smallest measured eccentricity ratio, and thus the highest static stiffness.