One mechanism by which laminar flow becomes turbulence is through the instability of vortex interaction. The nonlinear vvolution of the interactions between the A-vortex and the secondary closed vortex has been in-vestigated. This secondary closed vortex has been in-vestigated. This nonlinear instability process leads to some fundamental changes in the topology of flows Experi-mental observations are presented herre showing the for-mation of a chain of ring-like vortices,s which generate high-frequency spikes on time traces in a transitional boundary layer.