J1002-1-1 多層網を部分的に付加した円柱の空力音低減効果(流体関連の騒音と振動1)

概要

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Attaching a porous material or a pile fabric to the surface of a body in a flow is effective in reducing aeroacoustic sound generated by fluid-dynamic interaction between the body and the fluid flow. These materials are supposed to possess at least two principal functions: to soften the deformation and acceleration of vortices that are advected from upstream and collide with the body, and to weaken the strength of the vortices produced in the boundary layer around the body. In this study, the reduction in aeroacoustic sound that was obtained by a three-layer-mesh around a part of the surface of a cylinder was measured. The cylinder was set in a free jet from a rectangular nozzle. A mesh around the part where the upstream flow is turbulent achieves an equivalent sound reduction to a mesh wrapping the whole length of the cylinder ; a mesh around the part where the upstream flow is laminar indicates a smaller reduction only in low frequency range. The main mechanism of the sound reduction in this configuration is to soften the collision of upstream turbulence with the cylinder.
2009-09-12