Transient nonlinear analysis of lemon bore journal bearings using micropolar fluid lubrication

Abstract

This study investigates the stability characteristics of a lemon bore hydrodynamic journal bearing utilizing micropolar fluid lubrication. This study examines the influence of micropolar parameters on the dynamic stability of the bearing system via nonlinear transient analysis. The Reynolds equation, adapted to incorporate micropolar fluid theory, is solved numerically through the finite difference method utilizing the Successive Over-Relaxation technique alongside Swift–Stieber boundary conditions. The static and dynamic performance characteristics are evaluated computationally and validated with published results. The stability parameters, such as critical mass, threshold speed, and whirl frequency ratio, are computed for both Newtonian and micropolar lubricants to evaluate the impact of microstructural fluid characteristics. The trajectories of journal centres are determined by solving the nonlinear equations of motion using the fourth-order Runge–Kutta method, which facilitates a precise assessment of the system's stability margin. The findings demonstrate that the inclusion of micropolar effects significantly improves the stability margin of the journal bearing, especially in high load scenarios. Increased eccentricity results in a higher coupling number ( $N^2$ ) and a reduced characteristic length ( $l_m$ ), which enhance micropolar effects, thereby improving damping and expediting the convergence of journal trajectories to equilibrium.