ABSTRACT
Laboratory experiments were conducted with negatively buoyant freely falling cylinders at Reynolds numbers of 200–6000. The cylinder density ratio S = ρ/ρw and aspect ratio E = L/d were found to predict: 1) the onset of different modes of secondary motion ranging from oscillations to tumbling, 2) the maximum amplitude of the cylinder oscillations, and 3) the drag coefficient. Secondary motion reduces the time-averaged projected surface area of the cylinder during its descent, leading to a lower observed drag coefficient CD computed using the nominal projected area of length times diameter, Ld.
