Experimental evidence of an instability over an impedance wall in a duct with flow

Yves Aurégan; Maud Leroux

doi:10.1016/j.jsv.2008.04.020

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arXiv · 0809.3713

Experimental evidence of an instability over an impedance wall in a duct with flow

Yves Aurégan·Maud Leroux

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Abstract

An experimental investigation of the acoustical behaviour of a liner in a rectangu- lar channel with grazing flow has been conducted. The liner consists of a ceramic structure of parallel square channels: 1mm by 1 mm in cross section, 65 mm in length, and a surface density of 400 channels/inch square. The channels are rigidly terminated, thus constituting a locally reacting structure. In the absence of flow the liner reacts classically: There is a significant decrease in transmission coefficient around the frequency of minimal impedance. When the wall is exposed to a grazing flow this behaviour is changed: an increase in transmission coefficient appears at this resonance frequency. The transmission coefficient can be even rise above 1 (up to 3 for a Mach number of 0.3). This behaviour is caused by the appearance of a hydrodynamic instability above the liner. Furthermore, the stationary pressure drop induced by this liner is deeply affected by its acoustic behaviour. When a sound wave is added, at the resonance frequency of the liner, the pressure drop can increase by a factor 3 when the Mach number is 0.3. This effect is attributed to a modification of the turbulent boundary layer induced by the acoustic wave.

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Yves Aurégan, Maud Leroux. 2008-09-22. Experimental evidence of an instability over an impedance wall in a duct with flow. https://doi.org/10.1016/j.jsv.2008.04.020

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