Emergent dynamical scaling in the inviscid limit of 3D stochastic Navier-Stokes equation with thermal noise
In this work, we investigate the Navier-Stokes equation in the presence of thermal noise, both at finite viscosity (revisiting the seminal work by Forster-Nelson-Stephen) and in the inviscid limit, which has not yet been explored. We determine the space-time velocity correlations in this dynamics, using functional renormalisation group and direct numerical simulations. While spectrally truncated three-dimensional Euler flows reach a stationary equilibrium state, they exhibit non-trivial temporal correlations. We show that these non-trivial correlations persist for small but finite viscosity, yielding an emergent $\tau\sim k^{-1}$ dynamical scaling, where $\tau$ is the decorrelation time. We characterise the crossover from the scaling $\tau\sim 1/(\nu k^2)$, expected at large viscosity, to the scaling $\tau\sim 1/(u_{\rm rms}k)$ found in the inviscid limit.