| dc.description.abstract | High speed turbomachinery uses tilting pad journal bearing (TPJB) to support rotor loads (static and dynamic). Over the years, continuous efforts have produced machines operating at increasing operating speeds and specific loads. Large specific loads and high shaft surface speeds increase the bearing drag power loss, pad metal temperatures, and lubricant temperature. These high temperatures pose a bearing design limit when it comes to pad material properties. Thus, experimental data presenting solely the effect of pad material on the performance of TPJBs is highly beneficial.
The thesis presents and compares the static and dynamic force performance measurements of the copper-pads bearing (C-PB) and the steel-pads bearing (S-PB). Both bearings have the same geometric configuration and differ only by pad backing material (copper vs. steel). The bearing geometry includes: five pads, 101.6 mm bearing nominal diameter, 12.3 mm pad thickness, 0.4 L/D ratio, ball-in-socket pivot type, 50 % pivot offset, 63.5 µm nominal bearing radial clearance (Cb) and average pad preload (m) of 0.42. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s) to 14 krpm (74 m/s) and multiple bearing specific loads ranging from (0.17 MPa to 2.1 MPa). ISO VG 32 oil, at a supply temperature of 49 ºC, lubricates the bearings under a flooded lubrication configuration.
A comparison of the performance parameters for the C-PB and the S-PB show that the steel-pads bearing shaft operates with a 37 % higher eccentricity than the copper-pads bearing. The attitude angle is low (< 10º) for both bearings thus indicating low cross-coupling destabilizing forces. The oil temperature rise in the bearings is similar with maximum difference of up to 6 ºC. Further, the drag power loss measurement show that the steel-pads bearing has a low drag power loss and is ~ 5 % less than that of the copper-pads bearing. The maximum pad temperature rise is higher for the steel-pads bearing for all the operating conditions. However, it varies depending upon operating speed and bearing specific load. The difference in temperature between the S-PB and the C-PB ranges from 5 ºC to 16 ºC over the range of operating conditions.
The thesis also presents the dynamic load characteristics of the bearing. Over the range of operating conditions, the C-PB direct stiffness KvYY is up to 30 % larger than the SPB stiffness. Further, the difference in direct stiffness KXX between the C-PB and the S-PB ranges from 60 % to 90%. Moreover, the static load derived direct stiffness KvSTAT of the SPB is ~ 25-35% smaller than the dynamic load derived stiffness KYY whereas the C-PB KvSTAT is ~ 15-30% smaller than the C-PB KvYY. Similar to the stiffnesses results, the copper-pads bearing yields a high direct damping along both the loaded (CvYY) and orthogonal directions (CvXX). The CvYY is up to 25 % high and CvXX is up to 40 % higher for the C-PB. However, both bearings show high CvXX and CvYY symmetry. The virtual mass coefficients of both bearings are low (< 1.0). | |
