Fully developed isotropic turbulence: nonperturbative renormalization group formalism and fixed point solution

TL;DR

This paper applies a nonperturbative renormalization group approach to fully developed isotropic turbulence, revealing deviations from classical scalings and providing insights into intermittency mechanisms within the Navier-Stokes framework.

Contribution

It introduces a fixed point solution for turbulence using NPRG, highlighting deviations from classical theories and exploring intermittency emergence.

Findings

Fixed point solutions correspond to turbulence in 2D and 3D.

Deviations from Kolmogorov and Kraichnan-Batchelor scalings.

Identification of intermittency mechanisms within NPRG.

Abstract

We investigate the regime of fully developed homogeneous and isotropic turbulence of the Navier-Stokes (NS) equation in the presence of a stochastic forcing, using the nonperturbative (functional) renormalization group (NPRG). Within a simple approximation based on symmetries, we obtain the fixed point solution of the NPRG flow equations that corresponds to fully developed turbulence both in $d=2$ and $d=3$ dimensions. Deviations to the dimensional scalings (Kolmogorov in $d=3$ or Kraichnan-Batchelor in $d=2$) are found for the two-point functions. To further analyze these deviations, we derive exact flow equations in the large wave-number limit, and show that the fixed point does not entail the usual scale invariance, thereby identifying the mechanism for the emergence of intermittency within the NPRG framework. The purpose of this work is to provide a detailed basis for NPRG studies of NS turbulence, the determination of the ensuing intermittency exponents is left for future work.