平行2円柱から発生する空力音と流れ場への直交円柱の影響

概要

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Wire net often generates aerodynamic sound under some conditions in uniform flow. We simplified it by two parallel circular cylinders with cross cylinders. Separation of two parallel cylinders are four times the diameter . The effect of cross cylinders placed either at the upwind or downwind sides of two parallel cylinders are examined for various pitches(pz/dx=432) and angles of attack. With cross cylinders placed upwind, aerodynamics sound becomes intense in any pitch. But placed downwind, aerodynamics sound becomes weaker as the cross cylinder's pitch become narrower. Finally when separation of two parallel cylinders is equal to cross cylinder's pitch like a wire net. it doesn't generate noticeable sound. Measurements of the mean velocity field by LDV show that cross cylinders tend to elongate recirculation region of the upstream cylinder and to make the point of vortex roll up backward, leading to a weaker aerodynamic sound.