Measured performance of tilting-pad journal bearings over a range of preloads - Part II: Dynamic operating conditions

This article presents a comparison of the measured dynamic coefficients of five tilting-pad journal bearings with a range of preload factors. Each bearing had five shoes machined to a journal diameter of 70 mat, length-to-diameter ratio of 0.75, pivot offset ratios of 0.50, and a nominal assembled radial clearance of 81.3 mum. The rocker-backed tilt pads have nominal radial machined clearances of 176.8, 114.3, 91.4, 73.7, and 61.0 mum. These clearances constitute a range of preloads,from -0.333 to 0.540. Tested were both on-pad and between-pad orientations, with respect to applied forces. Dynamic coefficients are extracted from the test rig by applying sinusoidal synchronous,forces and measuring the resulting relative journal-to-bearing motion. A range of speed-load conditions was used, resulting in a Sommerfeld number range of 0.1 to 4.5. Measured dynamic coefficients (nondimensional principal and cross-coupled stiffness and damping coefficients) show the influence of preload. For the speed and load conditions included herein, the dynamic coefficients were not strongly dependent on the preload,factor. But very importantly the measured results demonstrate the reduced ability of tilting-pad journal bearings to satisfactorily operate in the negative preload regime for the bearings tested.