Load direction effects on measured static and dynamic operating characteristics of tilting pad journal bearings

Abstract

This paper presents a comparison of the measured dynamic coefficients, and the measured static characteristics for a tilting pad journal bearing operating at different load angles. Load angles of 0°, 18°, 36°, 54° and 72° were tested. The bearing had five pads and the journal diameter was 70mm, with a length to diameter ratio of 0.75. The pivot offset ratio was 0.50, and a nominal radial assembled bearing clearance, cb, of 74.9 μm was used. The rocker-backed pads had nominal radial ground in pad clearances, cp, of 109.2 μm, which yielded a preload factor of 0.314. Most tilting pad bearings are designed to operate with load on-pad or between-pads, although forces generated in the drive train can result in a bearing load in any direction. Measurements were made for two Sommerfeld numbers: 0.332 and 0.796. The test rig used for these studies has been previously documented. Dynamic coefficients were extracted from the test rig by applying sinusoidal and synchronous forces and measuring the resulting journal-to-bearing relative motion. The measured and reported parameters are eccentricity magnitude, attitude angle, and eight linearized dynamic coefficients (non-dimensional principal and cross-coupled stiffness and damping coefficients). The measured data presented in this may be used to assess the rotor dynamic performance of similar applications. The load angle had a moderate influence on operating eccentricity and attitude angle. For the speed and load conditions included herein, the dynamic coefficients were not strongly dependent on load angle. But very importantly the measured results demonstrate the ability of tilting pad journal bearings to satisfactorily operate at off-optimum load angles.