Краткое описание

We study experimentally the dynamics of the duct flow upstream of a high-Reynolds number swirling jet. Our setup involves a rotating honeycomb and allows to vary the contraction ratio of the final duct portion preceding the jet exhaust plane. Stereo-PIV measurements are realized in the duct directly upstream of these final portions, for increasing values of the swirl number. It is shown that the flow dynamics is strongly influenced by its supercritical or subcritical nature with respect to axisymmetric inertial waves. In the subcritical regime, complex mean flows are observed, which differ according to the duct geometry under consideration. Discrepancies are in turn detected in the flow unsteady behaviour, with the appearance, at the highest values of the swirl number, of transient small-scale recirculations located either close to the duct axis or near the edge of the boundary layer.