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
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.
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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