Abstract
• A revised model of calculating the time-dependent oil normal stiffness and tangential stiffness is proposed. • A numerical algorithm for high-speed spur gears lubricated by nanofluids is presented. • Spherical alumina nanoparticles significantly reduce friction coefficient and maximum temperature of total contact region. • Nanoparticles of higher concentration reduce traction friction and film temperature. • Many vortexes form and move from gear surface to pinion surface in rough contact. Nanofluids have excellent mechanical and thermal properties. Serious wear and high temperatures hamper the development of high-speed gear drives, and the application of nanofluids to gear lubrication is a potential solution. The main purpose of this paper is to investigate the mechanism by which nanofluids affect the lubrication performance of high-speed gear drives. A revised model of calculating the time-dependent oil normal stiffness and tangential stiffness is proposed. The density equation and viscosity equation are revised. Firstly, the numerical algorithm for high-speed spur gears lubricated by nanofluids is validated based on the classical minimum film thickness formula of Dowson, and then the differences between smooth and rough contact are analyzed. Furthermore, the effects of nanoparticle shape and concentration on tribology performance of gear lube are comprehensively investigated. Finally, the influences of surface roughness on film velocity field distribution are discussed. The simulation results indicate that applying spherical alumina nanoparticles to gear lube as additives is beneficial to the anti-wear performance of gear teeth and the lubricating property of lubricants, which considerably decrease friction coefficient and maximum temperature of the total contact region. Moreover, film normal stiffness of spherical alumina nanoparticles is close to base oil which means it maintains excellent load-carrying capacity. Higher concentrations of nanoparticles reduce the friction coefficient and maximum temperatures of the total contact region, and cause an increase in film tangential stiffness. The surface roughness remarkably influences film velocity field and high amplitude roughness induces formation of many vortexes in the contact center, and these vortexes move from gear surface to pinion surface in a total engagement cycle.
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