Effect of Reduced Oil Flow Rate On the Performance of a Load On Pad Journal Bearing: Flooded Vs. Evacuated Conditions

Abstract

Abstract Means to decrease the energy consumption of tilting pad journal bearings (TPJBs) are mandatory in a cost-efficient operation. Reducing the supplied flow is a method to diminish drag power losses, but a too low flow may produce too hot pad surfaces and subsynchronous vibrations (SSV). This paper addresses known issues via measurements of the load performance in a four-pad bearing configured as load-on-pad (LOP), either flooded or with evacuated ends. The nominal flow (Q) is proportional to shaft speed, and the supplied flow (Qs) ranges from 1.5 Q to ¼ Q. The evacuated bearing produces a slightly larger eccentricity. For the largest unit load of 2.07 MPa and shaft speed of 6 or 12 krpm, the highest pad temperature reaches ~ 130o C for Qs < 50% nominal. For both bearings, flooded or evacuated, drag power losses decrease ~30% as the supplied flow drops to 50% Q. The drag power grows as the applied load increases; the evacuated bearing produces ~ 40% lesser power than the flooded bearing. Both bearings produce similar size direct stiffnesses though largely orthotropic, Kyy >> Kxx. Direct damping coefficients Cxx ~ Cyy increase with shaft speed and load but dramatically decrease as Qs drops; the evacuated bearing being more sensitive. The LOP measurements and those for load-between-pads (LBP) [1,2] demonstrate the bearings safely operate with 50% Q. Alas, a too low flow significantly reduces the damping orthogonal to the load direction; the LOP evacuated bearing being prone to develop SSV Hash.