Active boundary layer tripping using oscillatory vorticity generator

The evolution of a train of vortex pairs ejected from a slot into a Blasius boundary layer was studied experimentally, with the aim of active boundary layer tripping. The excitation was directed upstream or downstream, at a shallow angle, or perpendicular to the surface. Vorticity, circulation, trajectories and convection speeds were calculated and used to describe the vortices' evolution. Intermittency, spectra and mean velocity profiles of the forced boundary layer were measured. It was found that shallow downstream directed excitation is very effective for promoting transition.