Non-linear behavior of the transfer impedance of a Micro-Slit-Plate: effect of slit length in presence of a bias flow

The influence of the slit length in presence of bias flow for a micro-slit plate (MSP) is investigated. MSPs are plates with arrays of slit-shaped perforations, with width of the order of the acoustic viscous boundary layer thickness. Micro-slit plates can be used for passive noise control of thermo-acoustic instabilities in combustion processes. During these processes, high amplitudes acoustic waves are generated and impact on the plates. The geometry discussed in this work is typical for manufacturing by cutting and bending the plate, without removing material. In previous works, in presence of high acoustic amplitudes, a significant difference between short and long slits was observed. In this work, the influence of a bias flow is investigated. This bias flow can also be used to control the wall temperature in hostile environment or for air-conditioning. Impedance tube measurements of the transfer impedance on accurately manufactured micro-slit plates in presence of bias flow have been performed. It appears that the presence of flow does not reduces the effect of the slit length on the transfer impedance of the micro-slit plate at high acoustic amplitudes.