Numerical investigation on windage losses of high-speed gears in enclosed configuration

Increasing efficiency of gearing systems is a key point in developing innovative aeroengines with low specific fuel consumption. The transmission system has a direct impact on the engine overall efficiency; thus, a performance optimization is an essential issue. In high-speed gearing systems, windage effects are extremely important and can dominate the other loss mechanisms. In this work, a comprehensive numerical study on windage losses experienced by a single spur gear rotating in an oil-free environment was carried out. Steady-state Reynolds-averaged Navier–Stokes calculations of the gear in free configuration were performed with conventional eddy viscosity models, comparing numerical predictions with experimental data from the open literature. The resulting modeling was exploited for simulating the same gear enclosed within cylindrical casings of various sizes, to assess the effect of the boundary walls on windage losses. The volume of fluid within the system was found to affect windage loss; therefore, results collected from the numerical analysis were exploited for developing a correlation aimed at predicting windage loss reduction with respect to the free configuration when the gear works within cylindrical casings. Finally, the predictive capability of formulation was assessed by exploiting experimental data available in the open literature, achieving a satisfying agreement.