3D PTV measurements on vortex structures induced by a free-falling sphere and sphere-wall interaction underwater

This work experimentally investigates the vortex structures induced by a single free-falling sphere and its wall interaction in initially quiescent water. Extensive time-resolved 3-dimensional particle tracking velocimetry measurements and digital object tracking analysis were carried out. The sphere begins to deviate from the vertical trajectory for running distancesL/D >5as the wake becomes unstable. This is associated with the shedding of a coherent vortex structure clearly resolved by the present measurements. The experiments provide insight into the vortex dynamics of a heavy spherical object settling in a dense fluid and reveal geometry-dependent sphere-wall interaction for different wall configurations. The results are useful for the validation of numerical schemes for solid/vortex interaction and collision modeling.