Experimental investigation of the acoustic damping of perforated liners with bias flow : part II

Through this project, the effectiveness of a cylindrical perforated liner with varying mean bias flow and grazing flow in its absorption of planar acoustic waves in a duct is investigated. The liner converts acoustic energy into flow energy through the excitation of vorticity fluctuations at the rims of the liner apertures. Vorticity is produced by fluid motion over a solid surface, the rate of production being greatest in regions where the pressure and velocity in the primary flow change rapidly, such as at corners and sharp edges. When sound waves are incident, vorticity diffuses from the edge and causes the sound to be damped. Moreover, the strength of this absorption can be increased by the appropriate configuration of the liner system in the duct. The entire sound incident on a perforated liner with bias flow can be absorbed if the flow speed and the geometry of the liner are chosen properly. An analysis of the single-liner and double liner system is performed to determine its absorbant capabilities in order to find the optimal design of liner systems with its corresponding flow speed. Through experimental analysis, we have reached the conclusion that a high bias flow coupled with a low grazing flow appears to generate the highest absorption strength.Bachelor of Engineering (Mechanical Engineering