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.
Keywords
Cite
@article{arxiv.1904.03079,
title = {Slow sound laser in lined flow ducts},
author = {Antonin Coutant and Yves Aurégan and Vincent Pagneux},
journal= {arXiv preprint arXiv:1904.03079},
year = {2020}
}
Comments
20 pages, 13 figures. V2: several clarifications added and Fig. 4 added