Abstract
For decades, journal bearings have been designed based on the half-Sommerfeld equations. The semi-analytical solution of the conservation equations for mass and momentum leads to the pressure distribution along the journal. However, this approach admits negative values for the pressure, phenomenon without experimental evidence. To overcome this, negative values of the pressure are artificially substituted with the vaporization pressure. This hypothesis leads to reasonable results, even if for a deeper understanding of the physics behind the lubrication and the supporting effects, cavitation should be considered and included in the mathematical model. In a previous paper, the author has already shown the capability of computational fluid dynamics to accurately reproduce the experimental evidences including the Kunz cavitation model in the calculations. The computational fluid dynamics (CFD) results were compared in terms of pressure distribution with experimental data coming from different configurations. The CFD model was coupled with an analytical approach in order to calculate the equilibrium position and the trajectory of the journal. Specifically, the approach was used to study a bearing that was designed to operate within tight tolerances and speeds up to almost 30,000 rpm for operation in a gearbox.
Highlights
Journal bearings are among the most widespread mechanical components
Simulations (Figure 4) were performed for different levels of eccentricity and the results reported in terms of Drag and Lift forces
forces are the fluid dynamic ones (FCFD) and g are known both in terms of direction and magnitude
Summary
Journal bearings are among the most widespread mechanical components. Their function is to support shafts carrying radial loads and to reduce friction. Thanks to the increasing computational power, more and more numerical methods were presented by several authors among which Mane et al [11] and Chauhan et al [12] who used computational fluid dynamics (CFD) to overcome the infinite length approximation These models do still not include vaporization, and the artificial substitution of negative values with the vaporization pressure is required. Aitken et al [19] developed a Newton–Raphson based approach including a simple vapor cavitation model for the study of big-end bearings. The author has already experience with bearings [20] He presented a full 3D numerical approach that includes the vaporization effects. The CFD model shows a good capability to estimate the pressure distribution along the journal, showing a difference with respect to the measurements of less than 5%. The inclusion of a vaporization model and the need of performing time-dependent simulations leads to an increase in the computational effort by 350 times with respect to the full-lubricated 3D simulation (whose results have to be artificially corrected replacing the negative values)
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