2025/06/10 by Arbon, Ryan, Bedrossian, Jacob
#Analysis of PDEs (math.AP) #FOS: Mathematics #Probability (math.PR)
paper · doi:10.48550/arxiv.2506.08769
We characterize the behavior of stochastic Navier-Stokes on \mathbbT × [-1,1] with Navier boundary conditions at high Reynolds number when initialized near Couette flow subject to small additive stochastic forcing. We take additive noise of strength ν1/2+ ΦdVt + ν2/3+α ΨdWt, where ΦdVt has spatial correlation in H03 and acts only on x-independent modes of the vorticity, while ΨdWt has spatial correlation in a lower order, anisotropic, Sobolev space H and acts on x-dependent-modes. We take the initial x-independent modes in the perturbation to be small in H03 in a ν-independent sense, while the non-zero x-modes are taken to be O(ν1/2 + α) in H. Letting ω solve the resulting perturbation equation, we split ω into the zero x-modes ω0 and the non-zero x-modes ω≠. We demonstrate an averaging principle holds wherein ω≠ is the fast variable and ω0 is the slow variable, deriving a closed nonlinear evolution equation on ω0 that holds over long time-scales (while the fast ω≠ modes solve a `pseudo-linearized' equation to leading order with dynamics dominated by inviscid damping and enhanced dissipation). This work can also be considered the stochastic analogue of the stability threshold problem for shear flows.