Journal Bearing: An Integrated CFD-Analytical Approach for the Estimation of the Trajectory and Equilibrium Position

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.

Scalable Technologies Achieving Risk-Informed Condition-Based Predictive Maintenance Enhancing the Economic Performance of Operating Nuclear Power Plants

“…The pressure in the lubricant is governed by the Reynolds equation. For an incompressible fluid with the no-slip condition, the stationary Reynolds equation in the continuum range is given by [23]:…”

“…Because the pressure is constant throughout the lubricant film thickness, COMSOL uses the tangential projection of the gradient operator, ∆ 𝑇𝑇 , to calculate the pressure distribution on the lubricant surface. In this case, (∆ 𝑇𝑇 𝑏𝑏 • 𝑣𝑣 𝑔𝑔 − ∆ 𝑇𝑇 𝑎𝑎 • 𝑣𝑣 𝑔𝑔 ) = 0, so the governing equation simplifies to [23]:…”

Effect of texture on hydrodynamic journal bearing performance under starvation lubrication

“…The calculated result is far from the actual situation. The calculation process of the half-Sommerfeld [7,8] boundary condition is similar to that of the Sommerfeld boundary condition. However, the half-Sommerfeld boundary condition does not accurately identify the location of the oil film rupture.…”

CFD Analysis of the Eccentricity Ratio on Journal Bearing due to Differences in Lubrication Type

“…In recent years, previous research has discussed fluid analysis and geometric variations either by simulation methods, experimental or both in overcoming damage or failure in bearings. Computational Fluid Dynamics (CFD) is a modeling technique widely used to simulate and evaluate based on fluids that work against components, such as hydrodynamic journal bearings, by matching actual conditions without the need to test first [8][9][10][11]. Previous research analyzed the influence of the ratio of eccentricity value to pressure distribution with a wide range of software such as ANSYS [12], COMSOL [13], MATLAB [14], and Fortran [6].…”