Loss compensation by flow in a corrugated resonant duct
Résumé
In this paper, the behaviour of a corrugated tube in presence of reflective boundary conditions and flow is experimentally studied. For the first time in (aero) acoustics, the gain and additional losses produced by the sound-flow interactions in the corrugations are measured by investigating the resonances of the cavity formed by the corrugated tube and the reflective boundaries. Depending on the flow velocity, the damping of the modes is increased or decreased by the sound-flow interactions. The damping rate of each mode will then depend on the balance between the initial system losses and the gain/losses brought by the corrugated part. Under certain conditions, loss compensation is achieved. This is highlighted by two experiments: one with a sweep sinus acoustic excitation and a measurement of the modes, one with a pulse input and a frequency-time analysis. For sufficient flow velocities, loss over compensation leads to the whistling of the tube at the frequencies of the amplified modes.
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