An experimental study of flow-induced noise from perforated pipes

An experimental study was performed to understand the generated flow noise by perforated pipes inside of concentric tube resonators. Six perforated pipes with 2% to 45% open areas and hole diameters ranging from 0.8 mm to 4.65 mm are considered. The six concentric tube resonators are compared to a straight pipe and a simple expansion chamber. All cases are tested at ten flow velocities ranging from 0.1 Mach to 0.28 Mach with a 0.02 Mach increment. The effect of the hole diameter and perforation rate on the noise generation and the overall level of the radiated noise is examined. It is found that the whistle frequency is inversely proportional to the hole diameter and proportional to the flow velocity. The amplitude of the generated flow noise is proportional to the perforation rate. Finally, an insertion loss method is used to demonstrate that minimizing the hole diameter and perforation rate decreases the generated flow noise.