Harbingers and latecomers - The order of appearance of exact coherent structures in plane Poiseuille flow

Abstract

The transition to turbulence in plane Poiseuille flow (PPF) is connected with the presence of exact coherent structures. In contrast to other shear flows, PPF has a number of different coherent states that are relevant for the transition. We here discuss the different states, compare the critical Reynolds numbers and optimal wavelengths for their appearance, and explore the differences between flows operating at constant mass flux or at constant pressure drop. The Reynolds numbers quoted here are based on the mean flow velocity and refer to constant mass flux, the ones for constant pressure drop are always higher. The Tollmien-Schlichting waves bifurcate subcritically from the laminar profile at $Re=5772$ and reach down to $Re=2609$ (at a different optimal wave length). Their localized counter part bifurcates at the even lower value $Re=2334$. Three dimensional exact solutions appear at much lower Reynolds numbers. We describe one exact solutions that is spanwise localized and has a critical Reynolds number of $316$. Comparison to plane Couette flow suggests that this is likely the lowest Reynolds number for exact coherent structures in PPF. Streamwise localized versions of this state require higher Reynolds numbers, with the lowest bifurcation occurring near $Re=1018$.

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Cited by in corpus (5)

• Small scale exact coherent structures at large Reynolds numbers in plane Couette flow
• Exact coherent states with hairpin-like vortex structure in channel flow
• Edge tracking in spatially developing boundary layer flows
• Transition to turbulence when the Tollmien-Schlichting and bypass routes coexist
• Pattern preservation during the decay and growth of localized wave packet in two-dimensional channel flow