A study on the stability performance of noncircular lobed journal bearings with micropolar lubricant

Abstract

In this paper, steady-state and stability performance characteristics of circular and noncircular two-, three-, and four-lobe journal bearings with micropolar fluids are presented. For this purpose, lubricating oil containing additives and contaminants is modeled as micropolar fluid. The modified Reynolds equation in dynamical state is obtained using the micropolar lubrication theory, and it is solved by finite element method. The bearing performance characteristics in terms of load carrying capacity, whirl frequency ratio, and critical mass parameter of journal are determined for different values of design parameters such as eccentricity and aspect ratio, preload factor, and micropolarity characteristics of lubricant in terms of material characteristic length and coupling number. Results show that in the case of noncircular bearings, the critical mass to load carrying capacity ratio decreases with increasing of preload factor, so for a constant vertical external load, the stability performance of rotating system can be improved by replacing the circular journal bearing with similar noncircular types. The results compared with Newtonian fluids indicate that micropolar lubricant exhibits better steady-state and dynamic performance. Also, results reveal that upgrading the micropolarity characteristics of lubricant causes increase in critical mass, load carrying capacity but decrease in whirl frequency ratio. It is also observed that the effect of micropolar fluids is more pronounced at high coupling numbers.