• drag reduction
• contoured cavities
• cfd simulation

The reduction of aerodynamic drag is of great interest for engineering applications and may also be seen as a first step towards the conception of control strategies that may eventually be applied to complex configurations.
The present work aims at reducing the aerodynamic drag on simple geometry.
A possible method to reduce these losses is to introduce suitably-shaped transverse cavities in the solid wall. These cavities will be efficient whether they alter the flow field so that the wall viscous stresses are decreased more than the pressure drag is increased. Contoured cavities are introduced in a flat plate solid wall. Both laminar and turbulent boundary layers have been considered at Reynolds numbers, based on the free-stream velocity, the flat plate length and the air's kinematic viscosity, that range from 2500 to 6 millions. Different shapes, numbers of cavities and dimensions are investigated.
Two-dimensional steady-state incompressible simulations have been carried out by using a commercial code and a finite-volume space discretization. A laminar DNS approach is used for the simulations of the flat plate with laminar boundary layer, while for the turbulent one a RANS approach with the transitional SST k-ω turbulence model with no wall functions is chosen. Cavities are positioned in different regions of the flat plate. For all the tested cases, the introduction of cavities reduces the aerodynamic drag compared to the one evaluated for the plat plate with laminar boundary layer in the same range. An optimization process of the cavities shape and depth, is then carried out to further decrease the aerodynamic drag. As for the flat plate with turbulent boundary layer, the increase of the pressure drag is instead equal or greater to the reduction in viscous stress, giving for all tested cases greater aerodynamic drag respect to the one calculated for the unmodified reference flat plate in the same range.