Effect of Rough –Slippery Coating and Micro-Pocket Geometry on Hydrodynamic Journal Bearing Performance

Advanced material coatings with surface energy lower than that of common liquid lubricants are often applied to reduce viscosityrelated energy losses in hydrodynamic journal bearings (HJBs).These low-surface-energy coatings are inherently slippery and exhibit slip boundary conditions at the contact interface.Studies indicate that, when combined with micro-scale regular surface roughness, such coatings enhance slippery behaviour and significantly reduce resistive forces at solid-liquid interface.Therefore, in present investigation, HJBs with low surface energy based slippery coatings incorporating random irregular surface roughness are considered.In addition to rough-slippery coating (RSC), HJBs with regularly shaped micro-pockets (MP) are also assumed.The variation of important tribological performance characteristics with change in RSC and MP attributes as well as with change in operating condition is calculated.To perform this investigation, the mass conserving average modified Reynolds equation, incorporating Gaussian roughness profile, Navier slip-length model, and viscous heating, is solved.The findings indicate that newly suggested optimized RSC zone profile is highly effective in reducing coefficient of friction and average lubricant temperature rise.Furthermore, the presence of MPs with suitable geometrical attributes and operating conditions contributes to additional performance gains in RSC bearings.The observations also indicate that, at constant external applied loads, variations in Sommerfeld number significantly influence effectiveness of HJBs with RSC and MP.