円柱後流渦による液体自由界面の振動と間欠的な気泡連行について

抄録

We conducted laboratory experiments on the flow around a circular cylinder moving at a constant velocity U₀ close to an air-water interface in order to understand interference between vortex-shedding frequency from the cylinder and the free surface wave. The vortex street and the free surface profile were visualized for Reynolds number (Re = U₀d/ν) between 200 and 15000 and for Froude number (Fr_h = U₀/(hg)^1/2) between 0.01 and 3.2 (d and h are the cylinder diameter and the distance between the top of the cylinder and the undisturbed water surface, respectively). At large Reynolds numbers (> 10⁴), the surface deformation becomes substantial in the downstream of the cylinder and intermittent bubble entrainment by a jet-like flow is observed. The wave oscillation and the vortex shedding frequency are synchronized when the bubble entrainment is observed. From the Strouhal-Reynolds number relationship with gap ratio (a = h/d) between 0.25 and 2.0, the Strouhal number of the wave oscillation and that of vortex shedding increase with decreasing the gap ratio a.