K BROCKWELL, MSc, DIC, CEng. MemSTLE, MIMechE and W DMOCHOWSKI, MSc, PhD
National Research Council Canada, Vancouver, Canada
S DeCAMILLO, BSc, MemSTLE, MamASME and A MIKULA, MBA, BSc, MemSTLE, MemASME
Kingsbury Inc., USA
Synopsis
This paper discusses the performance chacteristics of the leading-edge-groove (LEG) tilting pad
journal bearing and presents new experimental temperature data from a bearing operating with "on pad" and
"between pads" loading conditions, and with different bearing clearances. This data is then compared with
results obtained from a computer model of the LEG bearing. Good correlation between the theoretical and
experimental results suggests that the technique used in the model to calculate the temperature of the oil at the leading edge of the LEG journal pad is reasonably accurate.
The experimental data is collected from a 0.098 m diameter, five pad bearing, operating at shaft speeds up to 16500 rev/min and with unit loads up to 3 MN/m2. The paper also presents experimental results from bidirectional testing of the offset pivot LEG bearing, and finally discusses a technique for achieving substantial reductions in the power loss of the LEG bearing.
Introduction
The circular bore journal bearing may experience self
excited sub synchronous vibration during operation, and
although other bore modifications such as the multi-lobe
and offset halves designs are successful at raising the
stability threshold, only the tilting pad journal bearing
offers the possibility for eliminating oil film instability.
These unique characteristics were confirmed by Brockwell
et al. (1) in a series of experiments on a conventional
tilting pad bearing. They found that the cross-coupled
coefficients were negligible in comparison to the direct
coefficients, providing that there was geometrical and
"thermal" symmetry of the bearing. Ettles (2,3) considered
the effect of lack of symmetry on the performance of the
tilting pad journal bearing.
Because the tilting pad journal bearing is finding
increased usage in high power density machinery, interest
is focusing on the bearing's steady state performance. For
example, Brockwell and Dmochowski (4) found that,
during operation, significant changes to the bearing and pad
clearances may lead to a pad preload that is substantially
different to that specified in the initial design.
In recent years, a new design of hydrodynamic
bearing, known as the leading-edge-groove (LEG) tilting
pad bearing, has been the subject of further development
work. The LEG bearing is so named because the leading
edge of each pad is extended to accommodate an axial oil
distribution groove that directs a controlled amount of cool
lubricant into the hydrodynamic oil film. An earlier
experimental study (5) focused on a thrust version of the
LEG bearing, when tests on a 267 mm outside diameter
bearing at speeds up to 13000 rev/min indicated
significant reductions in frictional loss and bearing
operating temperature. More recently, a journal version of the LEG tilting pad bearing was the subject of
preliminary experimental and theoretical studies (6). This
work showed that the LEG bearing had significantly lower
operating temperatures to those of the conventional bearing;
a characteristic that was attributed to the reduction in hot
oil carry over between one pad and the next.
This paper is an extension of the work described by
Dmochowski et al. (6) and presents new experimental
temperature data from the LEG journal bearing for both
"on pad" and "between pads" loading conditions, and for
different bearing clearances. The experimental results are
compared with data from a computer model of the LEG
bearing. Furthermore, the paper discusses results obtained
from bidirectional testing of the LEG bearing, and
describes a technique for reducing the power loss of the
LEG bearing.
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