L12: Effect of Flow Rate on the Performance of a Flooded-Ends Tilting-Pad Journal Bearing Experiments and Predictions
Abstract
Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, relatively low pad temperatures, and ensuring a rotor dynamic stable operation End users focus on reducing the supplied oil flow rate into a bearing to lower operational costs and to increase drive power efficiency However, a too low oil flow might significantly rise pads’ (Babbitt) temperatures whilst increasing rotor vibrations due to a reduction in damping The lecture presents measurements of the steady-state and dynamic forced performance of a TPJB, flooded ends, whilst focusing on the influence of oil flow rate, 50% below and 150% above a nominal condition The spherical pivots test bearing has five pads with offset = 50% and preload ~ 040, and slenderness ratio L/D = 04 The test conditions include operation with shaft speed to 16 krpm (85 m/s surface speed) and specific static loads to 21 MPa under a load-between-pads (LBP) orientation A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant temperature Measurements include the journal static eccentricity and attitude angle, the drag toque, the oil exit temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial The measured drag power and the lubricant exit temperature rise depend mainly on shaft speed rather than on applied static load A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise of ~6°C in pads’ subsurface temperatures, a slight increase to 6% in the direct stiffnesses, and a decrease of 7% in the direct damping coefficients Conversely, a 15 times increase in oil flow rate causes a slight increase in drag power loss, max 9 %, a small drop in the pads’ temperatures (up to 3°C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping The paper also presents comparisons of the experimental results against predictions derived from a thermos-elasto-hydrodynamic (TEHD) lubrication model The most important finding relates to the measured bearing drag power differing significantly from a conventional estimate derived from the measured oil exit temperature raise and the supplied mass flow rate In short, the experimental results demonstrate a reduction in flow rate does not produce a significant drop in drag power losses for the test bearing
Description
LecturesCollections
Citation
San Andres, Luis; Thorat, Manish; Jani, Hardik; Kaizar, Hussain (2021). L12: Effect of Flow Rate on the Performance of a Flooded-Ends Tilting-Pad Journal Bearing Experiments and Predictions. Turbomachinery Laboratory, Texas A&M Engineering Experiment Station. Available electronically from https : / /hdl .handle .net /1969 .1 /197464.