Analysis of the inversion of the von Karman street in the wake of a confined square cylinder

This study considers the incompressible 2D laminar flow around a square cylinder symmetrically positioned in a channel. In this type of flow, even if vortices of opposite sign are alternately shed from the body into the wake as in the unconfined case, an inversion of their position with respect to the flow symmetry line takes place further downstream. Thanks to a dedicated numerical investigation, an interpretation of the inversion is given in terms of interference between the wake and the vorticity of the incoming flow, which is shown to play a dominant role in the phenomenon.