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）

摘要

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 partial deriv~2/partial deriv x_ipartial deriv x_j and partial deriv~2/partial deriv x_ipartial deriv 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 partial deriv~2/partial deriv x_ipartial deriv x_j and periodic sound buildups (edgetone) are suppressed as a result.%噴流が同軸上に設置されているくさび形状の物体にrn衝突する際，エッジトーン現象と呼ばれる自励振動現rn象が生じる．エッジトーン現象の発生機構は音のフィrnードバック機構で説明されている．