Abstract
This paper presents the change of non-dimensional characteristics and thermal behavior of different sized tilting pad journal bearings (TPJBs) with the same Sommerfeld number. A three-dimensional (3D) TPJB numerical model is provided considering the thermo-elastic hydro-dynamic (TEHD) lubrication model with pad thermal-elastic deformation. The pivot stiffness is assumed to be the combination of linear and cubic stiffness based on the Hertzian contact theory. The TPJBs in a configuration of load between pad (LBP) with the same Sommerfeld number having seven different sizes are simulated, and their non-dimensional dynamic and static characteristics and thermal behavior are compared. Pad thermal and elastic deformation are both taken into account. If the changes in lubricant viscosity, thermal deformation, and elastic deformation of journal/pads due to viscous shearing are ignored, the bearings with identical Sommerfeld numbers should show the same performance characteristics. However, the heat generation at the bearing clearance during operation (a) induces a decrease in viscosity and heat transfer to journal/pads and (b) results in a thermal deformation. Furthermore, the elastic deformation of the tilting pads and pivots also affects the bearing dynamic performance. For the same Sommerfeld number, the numerical analyses provide how the viscous shearing and elastic deformation lead to a change in bearing performance. For the small bearings with the same Sommerfeld number, the non-dimensional characteristics did not change significantly, where the heat generation was small being compared to the large sized bearing. The largest change in non-dimensional characteristics occurred when the maximum temperature of the oil film increased by 30 °C or more compared to the lubricant supply temperature. The root cause of the change in the non-dimensional characteristics is the viscous shearing in the oil film, and the thermal deformation of the structures surrounding the oil film acts in combination. These results provide insight into the Sommerfeld number, which can be used for the early stage of bearing design.
Highlights
In an initial stage of bearing design, Sommerfeld number is a good approximation to size the bearing and anticipate its performance
The root cause of the change in the non-dimensional characteristics is the viscous shearing in the oil film, and the thermal deformation of the structures surrounding the oil film acts in combination
These results provide insight into the Sommerfeld number, which can be used for the early stage of bearing design
Summary
In an initial stage of bearing design, Sommerfeld number is a good approximation to size the bearing and anticipate its performance. Identical Sommerfeld numbers for different sizes of bearings indicates the identical nondimensionalized static and dynamic force performance [1]. As Sommerfeld number is simple in nature, the assumptions for deriving Sommerfeld number neglect the effect of change in temperature influencing the decrease in viscosity and heat transfer to adjacent structures (bearing, shaft). The purpose of this paper is to give light to design engineers of the limitation of Sommerfeld number by providing how the tilting pad journal bearing (TPJB) performance differs. Sci. 2020, 10, 3529 with the thermal deformation, viscous shearing, elastic deformation of the tilting pads and pivots
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