Wake interaction of two disks falling in tandem

Abstract: The fluid dynamics video illustrates the interaction of two disks falling in tandem at Reynolds number close to 100. Two fluorescent dyes were used to visualize the wake of each body. We can observe that the trailing body accelerates thanks to the entrainment provided by the wake of the leading body and eventually catches up the leadind body. Then, thick disks (diameter/thickness = 3) lose their initial wakes, separate laterally and fall side by side. On the contrary, the wakes of thinner disks (d/t = 10) merge in a single wake and the bodies continue their fall together adopting a stable Y-configuration.