Collapse of transitional wall turbulence captured using a rare events algorithm

This text presents one of the first successful applications a rare events method for study multistability in turbulent flow without stochastic energy injection. The trajectories collapse turbulence plane Couette flow, as well their probability and rate occurrence are systematically computed using \emph{Adaptive Multilevel Splitting} (AMS). AMS computations performed system size $L_x\times L_z=24\times 18$ at Reynolds number $R=370$ with an acceleration by factor $\mathcal{O}(10)$ respect to DNS L_z=36\times 27$ $R=377$ $\mathcal{O}(10^3)$. results validated comparison 18$. Visualisations both systems indicate that collapses because self sustaining process fails locally. streamwise vortices decay elongated holes, leaving invariant velocity tubes experience viscous decay. These holes then extend spanwise direction. examination more than thousand $(E_{c,x}=\int u_x^2/2\,{\rm d}^3\mathbf{x},E_{c,y-z}=\int (u_y^2/2+u_z^2/2)\,{\rm d}^3\mathbf{x})$ confirms faster shows concentration trajectory. hints instanton phenomenology large limit. computation turning point states, beyond which laminarisation is certain, hole formation scenario it pronounced larger systems. Finally, non reactive trajectories, where opens closes, indicates opening closing distinct processes. Both streaks reform concomitantly when laminar close.