In this talk we will discuss the formation and dynamics of vortical structures in wall-bounded, plane parallel shear flows. These structures play an important role in the dynamics of intermittent turbulence in the near-wall region. In spatially periodic domains, this intermittency takes the form of a roughly periodic cycle of onset and collapse of turbulence. We show that the structures play an essential role in provoking the onset of turbulence, and present a theoretical model for their mathematical and physical origin. Experimentally, these flows are spatially as well as temporally intermittent, making it quite difficult to quantitatively define the characteristics of a structure. We discuss several methods of comparison of numerical and experimental data.

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