Performance evaluation of surface roughness on asymmetric hole-entry hybrid journal bearing operating under micropolar lubricant

Hybrid journal bearings are widely employed in high-speed applications due to their superior load-carrying capacity and improved stability compared to conventional journal bearings. The dynamic performance of such bearings can be further enhanced by incorporating an asymmetric hybrid hole-entry configuration in conjunction with surface roughness effects. In the present study, the Reynolds equation governing Micropolar lubrication in a journal bearing system is modified to account for surface roughness and is solved using the finite element method coupled with the constant-flow valve restrictor equation. Numerical results are presented for a prescribed applied load W ¯ o = 1.5 , a concentric design pressure ratio ( β * = 0.5 ) , and a variance ratio V ¯ r j = 0.5 under hybrid operating conditions. Bearing performance characteristics are evaluated for surface roughness parameters in the range Λ = 4 − 10 , considering different roughness orientations (γ), and for Micropolar lubricant parameters N 2 = 0.5 , 0.9 and l m = 10 , 30 . The results reveal significant improvements in dynamic coefficients when a longitudinally roughened bearing operates with a Micropolar lubricant. Compared to a smooth bearing lubricated with a Newtonian fluid, increases of up to 53.77% and 46.5% are observed in the stiffness coefficients, while enhancements of up to 34.11% and 35.63% are achieved in the damping coefficients of the fluid film.