Séminaire Fluide: Sébastien Gomé (Technion)

Turbulence often exhibits large-scale coherent structures when subject to external or body forces. I will discuss two cases where such self-organization emerges: wall-bounded flows and rotating flows.
In wall-bounded shear flows, large-scale turbulent–laminar patterns appear at low Reynolds number, in part due to the presence of a metastable laminar attractor. In pipe or plane Couette flow, this intermittency takes the form of discrete localized structures, sustained by the neighboring laminar flow. These structures proliferate via self-replication, driving a percolation process. I will show that in a controlled setup, the laminar–turbulent coupling can be suppressed, leading to a distinct transition scenario where turbulence propagates through fluctuating moving fronts - a mechanism possibly relevant to curved pipes, boundary layers, and stratified flows.
The second part will address rotating turbulence, where inertial waves generate two-dimensional large-scale flows. I will show that this two-dimensionalization follows from a hidden approximate invariant that constrains waves to transfer energy to large-scale 2D motions. Analytical and numerical results demonstrate that this coupling vanishes as rotation increases, revealing a phase transition from 2D-like to pure wave turbulence