Flexible sheets falling in an inviscid fluid

We use inviscid simulations to study falling flexible sheets in the two-parameter space of sheet density and bending rigidity. The basic behavior is a repeated series of accelerations to a critical speed at which the sheet flexes and rapidly decelerates, shedding large vortices. The maximum and average speeds of the sheet are closely related to the critical flutter speed. The sheet trajectories also show persistent circling, quasiperiodic flapping, and more complex repeated patterns. For small bending rigidity, the motion becomes less regular. At intermediate bending rigidity, trajectories show a well-defined falling angle relative to the vertical. For larger sheet density and bending rigidity, the overall motion is more horizontal. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432128]