Vortical structures in the wake of falling plates

Flow visualization and particle image velocimetry are applied to capture the flow fields generated by all three states of a falling plate in two dimensional passive flightfluttering, chaotic, and tumbling. The vortical structures are recorded in considerable clarity. Classic vortex shedding from different flight states are observed. The causes of more energetic tumbling mixing and localized fluttering disturbances are discussed. Strong, but small trailing processions of Karman vortex pairs or Kelvin-Helmholtz instabilities are found. It is also found that their formations are dependent on the trajectory, distinguishing the unique flow structures that different flight paths leave behind. The falling plate also induces a significant downwards convective motion. Further investigation shows that the wake trail and the convection contribute to the complex formation and dissipation of large vortical structures.