W. Dmochowski and K. Brockwell
Institute for Machinery Research, National Research Council Canada, 3650 Wesbrook Mall, Vancouver, B.C., V6S 2L2, Canada
Kingsbury, Inc., 10385 Drummond Road, Philadelphia, PA 19154, U.S.A.
Because of it's superior anti-vibration characteristics, the tilting pad journal bearing is a popular choice for supporting the shafts of rotating machinery. However, recent increases in shaft speed are causing concern about the high levels of bearing temperatures and frictional losses. Accordingly, a new design of bearing has been developed in which cool oil is supplied directly to the leading edge of each pad.
This paper presents results from the testing of a 0.098 m diameter, five pad bearing operating with a load of 11.1 kN and speeds up to 27S Hz. These experimental data are compared with results obtained from a three-dimensional thermohydrodynamic model of the tilting pad journal bearing. This model includes oil mixing at the leading edge of each pad. Good correlation between the experimental and calculated results has confirmed the hypothesis that hot-oil-carryover may be significantly reduced by supplying cool oU directly to the leading-edge-groove. Also, a comparison of results from the conventional and LEG bearings shows that the latter has substantially lower operating temperatures. Furthermore, calculations indicate that the power loss of the LEG bearing may be reduced significantly.
The tilting pad bearing, in either the thrust or journal configuration, is a popular choice of bearing for supporting the shafts of rotating machinery. However, machine operating speeds have now increased to the point where power loss and bearing metal temperature may be unacceptably high. A number of studies have, therefore. been aimed at improving bearing steady state performance [1,2]. Basically, apart from reducing the churning losses of the tilting pad thrust bearings. effort was focused on directing "fresh" oil to the leading edge of the pads. Bielec and Leopard  demonstrated the beneficial effect of supplying oil to nozzles located between the pads of a thrust bearing and a similar method was used for a tilting pad journal bearing . The authors of both papers claimed that by supplying oil under pressure to the oil film gap, the effect of hot-oil-carry-over was reduced.
The leading-edge-groove journal bearing offers a different approach. In this design, each pad is extended to accommodate an axial oil distribution groove, from which cool lubricant is introduced directly into the oil film. It has been shown that there are reductions in temperature and friction losses of both thrust [2, 5] and journal [6, 7] bearings when this method of oil supply is used.
Harangozo et al.  concluded that these oil supply methods had a greater effect on the performance of the thrust bearing and were less important in the case of the journal bearing. However, this conclusion was based on test results where the oil flow was fixed, regardless of bearing operating conditions. Recently, Fillon et al.  concluded that directed lubrication is effective at higher operating speeds (above 30 m/s).
In most cases, results from investigations into oil supply methods for tilting pad bearings have not been supported by theoretical considerations of the flow and heat exchange in the space between two adjacent pads. Some authors [4, 9] attributed the benefits of directed lubrication to a reduction in hot-oil-carry-over, but in their computer models the mixing coefficients were chosen without consideration of the bearing operating conditions.
Previous attempts to both explain and model the effect of the leading-edge-groove have been presented by the authors [6, 7]. In this paper, additional test results and theoretical data are presented to support the finding that the decrease in the operating temperature of the LEG bearing is through hot-oil-carry-over reduction. Furthermore, it will be shown that this effect is dependent on the oil flow rate. The results from the LEG bearing are compared with data from a conventional tilting pad journal bearing, and also with theoretical data from quasi three dimensional thermohydrodynamic computer models of the bearings. In these models, oil film turbulence and pad thermal and elastic distortions are accounted for. Full details are given in reference .
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