2010 Volume 76 Issue 772 Pages 2152-2159
We have conducted laboratory experiments on air-bubble generation by a submerged two-dimensional body moving at a constant velocity U_0 in order to understand the fundamental flow physics of marine constructions such as pipe lines close to the air-water interface. Measurements of the free surface profile and visualization of the air bubbles yield the threshold and the regime diagrams of the bubble generation, which are described by cross-sectional shape of the cylinders, Reynolds number (Re_d=U_0d/ν, where d and ν are the vertical thickness of the cylinders and kinematic viscosity of the water, respectively), Froude number (Fr_h=U_0/(gh)^<1/2>, where h is the depth of the cylinders), and normalized depth of the cylinder (a=h/d). For circular cylinders, as Re_d and Fr_h numbers increase, the surface deformation becomes substantial in the downstream of the cylinder and breaking wave with air entrainment occurs. The bubble generation by the breaking wave is also observed in the case of the elliptic cylinder although the condition of the bubble generation in the Re_d-Fr_h regime diagram is different from that observed in the case of the circular cylinder. In any cases of the cylinders, the ratio of the wave height to the wave length, which should be the physical criterion of the breaking wave with bubble generation, is about 0.1.