エッジトーン現象によって噴流中に形成された組織構造の特徴 : 第3報,渦構造への干渉によるエッジトーン現象のパッシブ制御(流体工学,流体機械)

概要

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The loud periodic sound buildups induced by edgetone oscillations were controlled by placing square bars at the location where the vortical structures get through. Two square bars were placed parallel to the spanwise direction of a nozzle and symmetric about nozzle centerline. When the square bars were placed at (L_x/b_e, L_y/b_e)=(5.0, ±1.0), the largest noise reduction was achieved and edgetone frequency showed higher value than the case without control system. The reason for the frequency change is probably explained by the fact that the feedback distance became shorter than the case without control system due to setting square bars, because the convection speed of vortical structures didn't change by this control. We also performed the phase average of the sound source term in Lighthill equation, and it was divided into ∂^2<u^^-_i><u^^-_j>/∂x_i∂x_j and ∂^2<u_<is>u_<js>>/∂x_1∂x_j. The former became smaller by the control, but the latter didn't change so much. This result implies that this control technique contributes to the ∂^2<u^^-_i><u^^-_j>/∂x_i∂x_j and periodic sound buildups (edgetone) are suppressed as a result.
社団法人日本機械学会の論文
2008-02-25