Parameterization of the in-water motions of falling cylinders using high-speed video

A methodology to observe the motions of large cylinders falling freely at large (~10⁶) Reynolds numbers using a stereometric, high-speed video technique is presented. Parameter variation in length, weight, center of mass, and nose shape combined with changes in release height and initial inclination angle were used to estimate the influence of net drag forces on six cylinder bodies. Cylinders with coincident centers of volume and mass typically assumed body orientations with the major axis aligned normal to the path of descent indicating that buoyancy forces and turbulent drag balanced the inertia of the body and displaced water. Displacement of the center of mass resulted in more vertical orientations and more complex motions. Abrupt changes in position, orientation, and velocity were also observed when air-dropped cylinders separated from a trapped cloud of bubbles signifying the onset of less predictable behaviors.