NONLINEAR INTERACTION AND THE TRANSITION TO TURBULENCE IN THE WAKE OF A CIRCULAR CYLINDER.

The transition and the development of turbulence in the near wake of a circular cylinder are investigated using hot-wire anemometry and flow visualization. The formation zone of the large regular vortices is studied in the subcritical regime, with and without the introduction of a splitter plate. Two different regimes are identified in the interaction between the von Karman vortices and those of the shear layer emerging from the separated boundary layer. Experimental evidence is given in support of the strong coupling at low Reynolds numbers characterized by phase modulations between the two types of structures. Spectral properties are used to describe the different stages of the interaction between the shear-layer vortices and the alternating ones. Physical properties of the interaction are examined separately in a numerical simulation using a pressure-velocity formulation. Additional study results are discussed.