This paper investigates the windage power losses generated by spur gears rotating in pure
air by using a computational fluid dynamics (CFD) code. The three-dimensional simulations
are at first validated comparing CFD predictions with the power losses measured in similar
conditions from other investigations. The volumetric flow rate which is expelled by the
teeth is then analysed, and a correlation which is based on a classical approach used in
turbomachinery is finally proposed which makes it possible to estimate windage losses for
spur gears. It was observed that this latter approach seems satisfying since the
formulation of the volumetric flow rate which is employed in the model is appropriate to
each gear.