Edge-Tone Instability: Effect of the Gas Nature and Investigation of the Feedback Mechanism

An experimental and numerical study of the edgetone phenomenon is reported. The purpose of the experimental part is to investigate the effect of the gas nature on the self-sustained instability. Comparisons between jets of air, Neon and CO₂ in air are performed. The corresponding numerical simulations are based on the two-dimensional resolution of the unsteady Navier-Stokes equations. Particular attention is paid to the spatial arrangement of the vortices generated at the edge tip. The values of the emitted frequencies are compared and discussed. It is shown that the gas density has a significant influence on both the flow pattern and frequencies that characterize the oscillation of the jet and the vortex shedding. Based on these results, some aspects on the mechanisms of the positive feedback generated by the edge on the jet are discussed.