Measurements of the Static Load (On Pad) Performance and Pad Temperatures in a Flexure-Pivot Tilting-Pad Bearing

Abstract

Measurements of the bearing displacements and pad edge temperatures in a four-shoe flexure-pivot tilting-pad bearing under static loading toward a pad are presented. The test rig consists of a vertical rigid journal and shaft supported on precision ball bearings and driven by a variable speed motor. The housing is suspended by cables and holds the flexure-pivot bearing with four 80° arc length pads, 50% offset and null preload. The length, diameter, and nominal radial clearance of the bearing are equal to 46 mm, 127 mm, and 0.178 mm, respectively, with a pad flexural rotational stiffness equal to 1125 N-m/rad. Steady-state tests with an ISO VG 22 oil are conducted at three rotational speeds (1800, 3000, and 4500 rpm) with loads applied to the bearing with a simple jack and load cell mechanism. Measurements include the bearing displacements in two orthogonal directions, oil flow rate, lubricant inlet and discharge temperatures, and the leading and trailing edge pad temperatures for each pad. The measurements show the bearing displacements to be larger in the direction of the applied loan than in the orthogonal direction with an attitude angle of approximately 30°. This characteristic bearing operation is due to the relatively large size of the bearing clearance and the pad rotational stiffness. The test bearing does not show any subsynchronous whirl (hydrodynamic instability) including operation at the null bad condition. The pad temperatures follow well-known trends with the highest magnitude at the trailing edge of the loaded pad. A reduction of the lubricant viscosity in the tests at the largest speed (4500 rpm) produced a drop in the bearing load capacity because of the increase of the lubricant and pad temperatures. Overall, the experimental performance curve of bearing eccentricity versus Sommerfeld number agrees well with numerical predictions based on an effective viscosity method. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997