Numerical Study on the Evaluation of Lubrication Performance of Journal Bearing

Abstract

A bearing is a mechanical element that supports shaft loads and assists in rotating the machine that cannot be excluded while discussing mechanical devices. Among them, journal bearings are used for high loads or high speed rotating motions due to their large area under loads and small friction coefficients. In the lubrication analysis of bearings, it is common to use Reynolds equation, which takes into account the low Reynolds number that can ignore the inertial terms compared to the viscous terms. However, as the eccentricity increases with higher loads and higher speeds, the flow becomes more complex, and for flows with high Reynolds number, it is necessary to simultaneously introduce the turbulence model and Navier-Stokes equation to calculate the viscosity flow. In this study, we analyze various factors affecting the bearing lubrication such as the lubrication temperature (50 ℃ , 100 ℃ , 150 ℃ , 180 ℃ , 200 ℃ ), the shape of the bearing (considering the dimple structure), the rotational speed (1000 RPM, 2000 RPM, 3000 RPM, 4000 RPM, 5000 RPM), and the eccentricity (0.6, 0.8 and 0.9). The elements that can determine bearing performance – such as pressure distribution of bearing parts, attitude angle according to the load on the shaft and volume fraction of lubricants in the gas state – were checked and compared according to Korea Standard (KS). The results showed that when the eccentricity and the rotational speed is increased and the lubricant temperature is lowered, the pressure on the bearings are increased. The results also matched well with the experimental results. By introducing the dimple structure on the bearing, the performance is improved when compared to that of the plain bearing. The dimple structure reduces the contact area between the shaft and the bearing, and the volume fraction reduction prevents erosion inside the bearing due to cavitation.