Falling/rising styles of gravity/buoyancy-driven disks
Abstract: Rigid disks falling under the effect of gravity in a viscous fluid, such as coins in water or confettis in air, may exhibit a large variety of non-vertical paths such as oblique fall, planar zigzag, complete tumble, etc. Recently, the combination of well-controlled experiments, global stability analyses and direct numerical simulations has resulted in significant progress in the understanding of the onset of the path instability of these objects and on the selection of their successive styles of fall or rise. Using some of this material, I will discuss the nature and geometry of the first non-vertical regimes of fall/rise as a function of the control parameters. I will also illustrate how global linear stability approaches and direct numerical simulations nicely complement each other to unravel the subtle mechanisms involved in this class of coupled fluid-body problems.
