Self-truncation and scaling in Euler-Voigt-$\alpha$ and related fluid models

TL;DR

This paper introduces a generalized Euler-Voigt-$eta$ model with derivatives of arbitrary order, demonstrating self-truncation behavior through high-resolution DNS and developing simplified models that reproduce key dynamics.

Contribution

The paper extends the Euler-Voigt-$eta$ model to arbitrary derivative orders, analyzes its self-truncation behavior, and introduces simplified models that match DNS results.

Findings

Self-truncation behavior observed at large $eta$

Self-similar growth of the truncation wavenumber $k_{st}$

Simplified models reproduce DNS intermediate-time dynamics

Abstract

A generalization of the $3D$ Euler-Voigt-$\alpha$ model is obtained by introducing derivatives of arbitrary order $\beta$ (instead of $2$) in the Helmholtz operator. The $\beta \to \infty$ limit is shown to correspond to Galerkin truncation of the Euler equation. Direct numerical simulations (DNS) of the model are performed with resolutions up to $2048^3$ and Taylor-Green initial data. DNS performed at large $\beta$ demonstrate that this simple classical hydrodynamical model presents a self-truncation behavior, similar to that previously observed for the Gross-Pitaeveskii equation in Krstulovic and Brachet [Phys. Rev. Lett. 106, 115303 (2011)]. The self-truncation regime of the generalized model is shown to reproduce the behavior of the truncated Euler equation demonstrated in Cichowlas et al. [Phys. Rev. Lett. 95, 264502 (2005)]. The long-time growth of the self-truncation wavenumber $k_{\rm st}$ appears to be self-similar. Two related $\alpha$-Voigt versions of the EDQNM model and the Leith model are introduced. These simplified theoretical models are shown to reasonably reproduce intermediate time DNS results. The values of the self-similar exponents of these models are found analytically.