Use of rectifying meshes for active noise control in an air flow duct

Abstract

At the application of an Active Noise Control (ANC) for a duct with high speed flow whose velocity is around 12.0m/s (Reynolds number of 1.0×10⁵), the following resultsfor the use of the meshes, as the simplest method for rectifying the flow, were given. The effect of ANC depends on the disturbance velocity attenuation factor of the rectifying meshes. The meshes should not be installed closer to the detection sensor than half the diameter of the duct. The meshes are more effective than the use of thicker sound absorbent materials on the sensors, although the numerical aperture of duct cross-section can be decreased both. The noise reduction effect by use of the meshes were around 3 to 4dB, without ANC under 200Hz, and 13dB of noise control effect at 500Hz with the ANC system with the meshes (These effects were measured 100mm from the duct outlet).