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Turbulent-laminar patterns

The transition to turbulence is characterised by coexistence of laminar and turbulent regions. In plane Couette and Poiseuille flow, this coexistence takes the form of statistically stationary alternating oblique bands of turbulent and laminar flow whose wavelength and orientation with respect to the streamwise direction are fixed. Since the wavelength of these astonishing patterns is much larger than the gap, they were first discovered in very large aspect ratio experiments. We study these patterns via full direct numerical simulation and reduced models.