Investigation of the impedance of a micro-perforated plate with two-sided grazing flow

Acoustic impedance for perforates is mainly quantified by semi or totally empirical formulas, which depend on the experimental set-up used and are specific for each type of tested sample. In this work, the acoustic impedance of a micro-perforated plate (MPP) with two-sided low Mach grazing flow is educed by a modified semi-analytical inverse technique. The inputs to this technique are complex acoustic pressure measured at eight positions at the wall of the duct, upstream and downstream of the MPP section. Several measurements on the two sided grazing flow rig are conducted and trends in the impedance shift are observed. These trends serve to quantify the change in the resistance and reactance of a MPP when it is subjected to two sided grazing flow. An empirical formula is also proposed which is based on these trends. This formula helps in approximating the behavior of MPP’s in applications such as perforated cooling fans, perforated guide vanes, and turbine nozzles. It was observed that with increased flo...