  The impact of fluidic actuation on the wake and drag of a three-dimensional
blunt body is investigated experimentally. Jets blowing tangentially to the
main flow allow to force the wake with variable frequency and amplitude.
Depending on the forcing conditions, two flow regimes can be distinguished.
First, in case of broadband actuation with frequencies comprising the natural
wake time scale, the convection of the jet structures enhances wake
entrainment, shortens the length of the recirculating flow and increases drag.
Secondly, at higher actuation frequencies, shear-layer deviation leads to
fluidic boat-tailing of the wake. It additionally lowers its turbulent kinetic
energy thus reducing the entrainment of momentum towards the recirculating
flow. The combination of both mechanisms produces a raise of the base pressure
and reduces the drag of the model. Both actuation regimes are characterized by
complementary velocity, pressure and drag measurements at several upstream
conditions and control parameters. By adding curved surfaces to deviate the
jets by the Coanda effect, periodic actuation is reinforced and drag reductions
of about 20% are achieved. The unsteady Coanda blowing not only intensifies the
flow deviation and the base pressure recovery but also preserves the unsteady
high-frequency forcing effect on the turbulent field. The present results
encourage further development of fluidic control to improve the aerodynamics of
road vehicles and provide a complementary insight into the relation between
wake dynamics and drag.
