Windage losses arise due to the viscous dissipation of air -oil mist flow driven by the rotating faces, sides of the gears in a gearbox. The windage losses can consume up to 3% of the transmitted power. In the open literature, theoretical investigations mostly focused on the single phase (air) flow. In the present study we attempt to elucidate the complex flow physics between the gears by considering the effects of oil particles in the air flow. The goals of this work is to develop a physical understanding of the aerodynamics of gear windage loss. A spur gear geometry was considered, for which experimental and theoretical data are available. A commercial Computational Fluid Dynamics algorithm (CFD++) was utilized for the numerical simulations. The first group of simulations were performed for a single phase (air) flow in order to validate the numerical approach. The results showed good agreement with the experiment. Various shrouding configurations and free spinning cases are studied at different rotation speeds of the gear. The effects of the oil droplets on the windage losses were quantified.

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