Abstract
Instabilities and vortical structures in the near wake of spheres and circular disks are reviewed, together with those of elliptic disks and rectangular disks which have two length scales. The linear global instability analysis (Natarajan & Acrivos 1993) yields critical Reynolds numbers of regular and Hopf bifurcations of the sphere wake, which are in excellent agreement with direct numerical simulations and experiments. The Strouhal number of shedding of hairpin-like vortices in the sphere wake is significantly dependent on Reynolds number, reflecting changes in vortex structure in the wake such as transition from laminar to turbulent flow. The vortex structure at high Reynolds numbers still remains to be clarified. Two periodic components exist in the wake of elliptic disks and rectangular plates of aspect ratio of 2 and 3, being caused by global instability in the near wake.
