DYNAMICAL CHARACTERIZATION OF THE SPATIOTEMPORAL STRUCTURES IN THE WAKE OF A BLUFF-BODY

Singular systems analysis (SSA) and cluster analysis are used to map o ut and characterize the three-dimensional spatiotemporal structures en countered in the wake of a finite-aspect-ratio circular cylinder. The evolution of the wake structure - determined using experimentally obta ined velocity time series - was studied as it underwent transition in the range of Reynolds numbers 100 to 200. Using these techniques impor tant new features in the wake structure are identified: for example, i t is seen that the whole of the pre-transitional wake is simply ordere d by the nonlinear mixing of modes generated in the near wake region, whilst, after transition, a localized region of turbulence exists. (C) 1996 Academic Press Limited