Characterisation of a coupled phenomenon in a confined shear-layer

Experimental measurements in a confined chamber with injection through porous walls were carried out over a range of low characteristic velocity levels in order to analyse the vortex shedding phenomenon in the wake of an emerging obstacle and its coupling with the confined chamber acoustics. Two trends were identified at subsonic velocities. At lower velocities, a weak coupling was observed and the hydrodynamics could force a shifting of the resonant acoustic frequency. Turbulence behaviour greatly influenced the dissipation of coherent structures. Nevertheless, the coupling phenomenon strengthened at higher velocities. It caused the natural self-sustained shear-layer to align with the first longitudinal acoustic mode and generated a complete resonant state in the whole chamber.