MODIFICATION OF BACKWARD-FACING STEP FLOW BY ACOUSTICAL WAVE

The effect of an acoustic wave excitation on a separated flow due to a two-dimensional backwardfacing step has been studied experimentally in order to qualify the influence of the excitation on the flow parameters and define a dedicated actuator and an active control strategy. Flow visualizations with associated image processing show an increasing of the structure coherence, a better periodicity in vortex formation and a decrease of structure formation and pairing lengths. Moreover, we obtain an increase of pulsation number in the recirculating zone and a better periodicity of these pulsations. Unsteady pressure measurements registered in different flow locations, show off energy increase for the instability frequencies and the corresponding pairing. Several excitation amplitudes have been studied in different configurations. Only small amplitude is required to observe previous tendencies. These results allow us to define an actuator with a specific frequency band. Experimental identification is carried out in order to define an appropriate control strategy. Nomenclature