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Slow sound laser in lined flow ducts

Abstract : We consider the propagation of sound in a waveguide with an impedance wall. In the low frequency regime, the first effect of the impedance is to decrease the propagation speed of acoustic waves. Therefore, a flow in the duct can exceed the wave propagation speed at low Mach numbers, making it effectively supersonic. We analyze a setup where the impedance along the wall varies such that the duct is supersonic then subsonic in a finite region and supersonic again. In this specific configuration, the subsonic region act as a resonant cavity, and triggers a laser-like instability. We show that the instability is highly subwavelength. Besides, if the subsonic region is small enough, the instability is static. We also analyze the effect of a shear flow layer near the impedance wall. Although its presence significantly alter the instability, its main properties are maintained. We also point out the analogy between the present instability and a similar one in fluid analogues of black holes known as the black hole laser.
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https://hal.archives-ouvertes.fr/hal-02336989
Contributeur : Yves Aurégan <>
Soumis le : mardi 29 octobre 2019 - 11:19:35
Dernière modification le : jeudi 4 mars 2021 - 14:48:22
Archivage à long terme le : : jeudi 30 janvier 2020 - 14:40:24

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Antonin Coutant, Yves Aurégan, Vincent Pagneux. Slow sound laser in lined flow ducts. Journal of the Acoustical Society of America, Acoustical Society of America, 2019, 146 (4), pp.2632-2644. ⟨10.1121/1.5128310⟩. ⟨hal-02336989⟩

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