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

Abstract Singular systems analysis (SSA) and cluster analysis are used to map out and characterize the three-dimensional spatiotemporal structures encountered in the wake of a finite-aspect-ratio circular cylinder. The evolution of the wake structure —determined using experimentally obtained velocity time series —was studied as it underwent transition in the range of Reynolds numbers 100 to 200. Using these techniques important new features in the wake structure are identified: for example, it is seen that the whole of the pre-transitional wake is simply ordered by the nonlinear mixing of modes generated in the near wake region, whilst, after transition, a localized region of turbulence exists.