A study of the response of a round jet to pulsed fluidic actuation

Resumo

Steady and unsteady uidic actuators, in the form of secondary control jets injecting from the nozzle lip, aimed at jet noise reduction, are investigated. Three different geometric congurations are tested: non-converging control jets, Open fluidic triangle convergence and Closed fluidic triangle convergence. By means of a triple decomposition of hot-wire data and a scale-separation argument, the low-frequency perturbation (near-nozzle dynam- ics) and jet response (downstream dynamics) of the ow are studied. Comparison of the phase-averaged component of the decomposition with predictions of linear stability theory (LST) suggest that two qualitatively different responses are active: at the main forcing frequency the jet response looks to be non-linear; at two secondary, higher frequencies, LST gives reasonable predictions for the local growth rates and convection velocities. The considerably lower convection velocity of the non-linear component of the ow response suggests that this control mechanism may constitute a useful manner by which to reduce the effciency of wavepacket sound sources associated with coherent structures. © 2011 by the author(s).