Effect of Flow Rate on the Performance of an Evacuated Tilting Pad Journal Bearing: Load on Pad vs. Load-Between-Pad Configurations

Reducing the oil flow supplied to a fluid film bearing decreases the drag power loss and increases efficiency, though with increased pad temperatures and a drop in damping. Savings in pumping and lubricant storage make the case for low flow. The paper reports further measurements of performance in a tilting pad journal bearing with evacuated ends and configured as load on pad (LOP) and load between pads (LBP). The supplied flow (Q) ranges from 150% to 25% of a nominal flow rate (Qs). Operation is at a constant shaft speed of 6 krpm and with unit loads as large as 2.07 MPa. Both bearings operate slightly more eccentrically as Q < Qs, the LBP bearing displacing more. Pad temperatures are similar for both bearings, although the LOP bearing runs cooler and its oil exit temperature is also lower as Q decreases. The bearings main stiffness (Kyy) increases with load, the LOP bearing producing 25% more stiffness that increases as Q decreases. The LOP bearing produces small Kxx that quickly decreases for Q = 25% Qs. The LBP bearing does produce significant Kxx ~ Kyy, both slightly affected by flow reduction. The main damping Cyy for the LBP bearing drops quickly for the lowest Q, whereas Cyy for the LOP bearing remains unchanged. Similarly, Cxx for the LBP bearing varies little with Q decreasing, while for the LBP bearing, Cxx \(\to\) 0 for the lowest Q. The measurements show the LBP bearing performs better at low flows whereas the LOP bearing losses both stiffness and damping for the lowest Q. At this low flow, the bearing produced low frequency shaft motions (SSV Hash).