Effect of Pad Material, Copper Vs. Steel, On the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

The paper presents measurements of performance conducted on a copper pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads' backing material, copper vs. steel. The journal diameter D=102 mm, and a bearing has five pads with length L=0.4D, nominal radial clearance 0.064 mm. The bearings operate at four shaft speeds ranging from 6 krpm to 14 krpm and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. At the highest load (on pad) and low speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads' peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ~ 5% lower drag power loss than that in the C-PB. From dynamic load test results, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB.

Measurements to Quantify the Effect of a Reduced Flow Rate On the Performance of a Tilting Pad Journal Bearing (LBP) with Flooded Ends

Operation of tilting pad journal bearings (TPJBs) with a reduced flow improves system energy efficiency by reducing drag power losses, albeit the temperature rise in both the bearing pads and the lubricating oil become a concern. This paper presents measurements of the static and dynamic load performance of a flooded ends TPJB with flowrates ranging from 150% to ~5% of a nominal supply condition. The test bearing is a four-pad, 102 mm diameter, center pivot, with single orifice feeds, and configured with end seals. Experiments include operation at two shaft speeds = 6 krpm and 12 krpm and under three specific loads = 0.345 MPa, 1.03 MPa and 2.07 MPa applied in between pads (LBP). The measurements show the bearing drag power loss decreases by nearly 20% when flow rate drops to 50% of nominal. However, halving the flow produces a raise in pad subsurface temperatures, ~7 °C for operation at 12 krpm. Flow reduction below 50% results in substantial power savings; however, it also produces too hot pad temperatures that approach a known limit for Babbitt material safe operation. Damping coefficients decrease by ~30% as the flow rate decreases from 150% to just a few % of nominal flow. The experimental results are first to quantify operation of a TPJB supplied with minute amounts of lubricant flow. A test with a very low flow rate at ~2% of nominal and under a light load produced the emergence of a broadband subsynchronous vibration frequency, albeit with very small amplitude.

Impact Dynamics in Four-Segment Tilting Pad Journal Bearings Subjected to Pad Fluttering

This paper presents a transient analysis of the motion of unloaded upper pads in a tilting pad journal bearing. It is known that such pads can exhibit self-excited vibration called pad fluttering, which can initiate fatigue damage due to elastic contacts between the fluttering pad and the journal. Unlike previous studies, this work attempts to evaluate forces in the contact. This evaluation is done using a robust nonlinear model, which considers hydrodynamic lubrication, out-of-balance forces and Hertzian contacts. Furthermore, qualitative changes of the bearing’s components motions are analysed in a wide range of journal speeds using bifurcation diagrams, phase portraits and estimates of the largest Lyapunov coefficients. The analysis reveals the intriguing nature of the system, which bifurcates between the periodic motion, period-doubling and chaos.