Active Control of Vortex Breakdown Phenomenon in the Wake of a Simplified Car Geometry

The breakdown of longitudinal vortices originating from the rear pillars of a simplified geometry of automobile vehicles is obtained with a view to reducing aerodynamic drag. Numerical experiments are conducted on an Ahmed body according to a computation code based on the Lattice Boltzmann Method (LBM). Vortex breakdown is obtained by a continuously and uniformly blowing at the separation line prompting the formation and maintenance of the vortex. The breakdown is characterized by a sudden disintegration of the vortex core and the appearance of a recirculation zone. Numerical results obtained at several blowing velocities reveal the critical impact of the Swirl number on vortex breakdown. Moreover, breaking down the longitudinal vortices induces an increase in the static pressure at the wall of the rear window, which can bring about drag reductions close to 6%.