Spatio-temporal evolution of isolated turbulent bands in channel flows

Abstract eng:
We introduce an experimental set-up that enables us to create two dimensional shear flow with zero mean advection velocity. We investigate a plane Couette-Poiseuille configuration, completing the first experimental results for this flow which had only been studied theoretically to-date ([5]). Using flow visualizations we characterize subcritical transition to turbulence and we show the existence of turbulent spots in plane Couette-Poiseuille flow. Due to zero mean advection velocity of the base profile, these turbulent structures are nearly stationary (despite a non-zero pressure gradient in streamwise direction). We ascertain two characteristic wavenumbers correspond to two different inner regions of the base flow. We also determine the evolution of streamwise and spanwise dimensions of turbulent spot as a function of Reynolds number.

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