This master thesis focuses in the study of the application of active flow control in the transitional regime (Re ≈ 3E3) at the rear part of the roof of a 2D Ahmed body geometry. To do so, the natural bifurcations of the problem (which separate the ordered laminar behavior from the first pre-turbulent chaotic behavior) are studied, and different actuation frequencies and amplitudes are tested. The results are compared to the non-actuated case and to constant suction. Actuation at frequencies equal or larger than the natural vortex shedding frequency are observed to resonate with the wake, forcing the shed vortices to adapt, greatly reducing drag and increasing lift. These drag reductions are comparable to those obtained under a constant suction and are related to the rear base vortex shedding frequency. Actuation at lower frequencies, however, does not significantly alter the wake topology and changes to the global forces are minor.