Effets d'une tuyère convergente sur un écoulement tournant

We study the flow in the exit plane of a high-Reynolds swirling jet generated with a rotating honeycomb followed by a converging nozzle. Hot-wire measurements downstream of two nozzles of different contraction ratios show that the flow progressively becomes turbulent for the same values of the swirl number characterising the flow upstream of the nozzles. To understand this phenomenon, we investigate the pipe flow located between the exit of the honeycomb and the exit plane of the nozzles. A simple stationary model is first introduced, which shows that a recirculation is likely to occur at the nozzle wall when the upstream flow is critical with respect to inertial waves. We then show that these solutions are globally stable to axisymmetric disturbances, but may strongly enhance short-scale perturbations on their trajectory from the outlet of the honeycomb to the exit plane of the nozzles.