  The flow downstream a backward-facing step is controlled using a pulsed jet
placed upstream of the step edge. Experimental velocity fields are computed and
used to the recirculation area quantify. The effects of jet amplitude,
frequency and duty cycle on this recirculation area are investigated for two
Reynolds numbers (Re=2070 and Re=2900). The results of this experimental study
demonstrate that upstream actuation can be as efficient as actuation at the
step edge when exciting the shear layer at its natural frequency. Moreover it
is shown that it is possible to minimize both jet amplitude and duty cycle and
still achieve optimal efficiency. With minimal amplitude and a duty-cycle as
low as 10\% the recirculation area is nearly canceled.
