MEASUREMENTS OF THE STATIC LOAD (ON PAD) PERFORMANCE AND PAD TEMPERATURES IN A FLEXURE-PIVOT TILTING-PAD BEARING

Measurements of the bearing displacements and pad edge temperatures in a four-shoe flexure-pivot tilting-pad bearing under static loading to ward a pad are presented. The test rig consists of a vertical rigid jo urnal and shaft supported on precision ball bearings and driven by a v ariable speed motor. The housing is suspended by cables and holds the flexure-pivot bearing with four 80 degrees are length pads, 50% offset and null preload. The length, diameter, and nominal radial clearance of the bearing are equal to 46 mn, 127 mm, and 0.178 mm, respectively, with a pad flexural rotational stiffness equal to 1125 N-m/rad. Stead y-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 wit h a simple jack and load cell mechanism. Measurements include the bear ing displacements in two orthogonal directions, oil flow rate, lubrica nt inlet and discharge temperatures, and the leading and trailing edge pad temperatures for each pad. The measurements show the bearing disp lacements to be larger in the direction of the applied loan than in th e orthogonal direction with an attitude angle of approximately 30 degr ees. This characteristic bearing operation is due to the relatively la rge size of the bearing clearance and the pad rotational stiffness. Th e test bearing does not show any subsynchronous whirl (hydrodynamic in stability) including operation at the null load condition. The pad tem peratures follow well-known trends with the highest magnitude at the t railing 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 b earing load capacity because of the increase of the lubricant and pad temperatures. Overall, the experimental performance curve of bearing e ccentricity versus Sommerfeld number agrees well with numerical predic tions based on an effective viscosity method.