Measurements to Quantify the Effect of a Reduced Flow Rate on the Performance of a Tilting Pad Journal Bearing With Flooded Ends
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AbstractOperation 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 60C, and with a flow rate ranging from 150% to just 5% of a nominal supply condition. The flow range covers both over-flooded and starved flow conditions. The test bearing is a four-pad, 102mm 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 (= 64m/s surface speed) and under three specific loads=0.345MPa, 1.03MPa, and 2.07MPa applied in between pads (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, 7C 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 130C, a known limit for Babbitt material safe operation. The bearing static eccentricity (e) and direct stiffnesses Kxx>Kyy (load direction) do not show a significant dependency on the supplied flow, either above or below the nominal condition. A minor stiffness hardening does occur for very low flow conditions, 5% or so of nominal. Damping coefficients (CxxCyy) decrease by 30% as the flow rate decreases from 150% to just a few % of the nominal flow. The experimental results are first to quantify the 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 (SSV) frequency, albeit with a very small amplitude.
