Several different types of gears

yet with similar size

were simulated. The air flow around gear teeth and the pressure distribution on gear teeth surfaces were studied. The windage losses of a specific internal bevel gear adopted in an aero engine was calculated. Result showed that， gear windage losses were consist of pressure loss and viscous force loss

and viscous force loss occupied ratio of 4%-17%. 60% difference in windage losses of helical gears with opposite hand of helix suggests the effect of wall. Windage losses for internal bevel gear in aero engine occupied about 49% of total transmission losses.