Flow Past a Partially-Submerged Cylinder

Flow past a partially-submerged cylinder. At sufficiently high Froude number, the vorticity shed from the cylinder is strongly coupled with time-dependant undulations of the free-surface. At Fr = 1.19, the free-surface exhibits large-amplitude undulations. Immediately downstream of the first and second troughs, large-scale swirl patterns of velocity vectors are apparent. The corresponding image of the vorticity distributions shows that small-scale vorticity concentrations, due to a Kelvin-Helmholtz (K-H) instability, are formed form the bottom surface of the cylinder. Coalescence of a number of the K-H vortices leads to formation of large-scale clusters of vorticity adjacent to each trough of the free-surface. At a higher value of Fr = 1.75, the mean elevation of the free-surface decreases substantially. Concentrations of vorticity from the bottom surface of the cylinder are convected beneath the free-surface and merge with the vorticity layer arising at the onset of classical wave breaking. Re = 10,865 and 15,380. [21]