58771 - 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 decreases pumping costs and oil sump storage. A low supplied oil 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 lubricated with an ISO VG 46 oil, supplied at 60 ^oC, and with flowrate ranging from 150% to just ~5% of a nominal supply condition. The flow changes cover both the over-flooded and starved flow conditions. The test bearing is a four-pad, 102 mm in diameter, center pivot, with single orifice feeds, and configured with end seals to flood the bearing housing. The experiments include operation at two shaft speeds = 6 krpm and 12 krpm (= 64 m/s surface speed) and under three applied specific loads = 0.345 MPa, 1.03 MPa and 2.07 MPa (LBP). The measurements show the bearing drag power loss decreases by nearly 20% when the flow rate drops to 50% of nominal. However, halving the flow produces a raise in pad subsurface temperatures, ~7°C increase for operation at 12 krpm. Flow reduction below 50% does result in even more substantial power savings; however, it also produces too hot pad temperatures that approach 130 ^oC, a known limit for Babbitt material safe operation. The bearing static eccentricity (e) and direct stiffnesses K_XX < K_YY (load direction) do not show a significant dependency of the supplied flow rate, either above or below the nominal condition. Some minor stiffness hardening does occur for very low flow conditions, 5% or so of nominal.  Damping coefficients (C_XX ~ C_YY) 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.