Restricted Euler dynamics in free-surface turbulence

TL;DR

This paper develops a restricted Euler model for free-surface turbulence, comparing it with high-resolution experimental data to understand velocity gradient behavior and surface flow intermittency.

Contribution

It introduces a simplified Euler model for free-surface turbulence and compares its predictions with experimental data, revealing key differences and flow characteristics.

Findings

Model captures unstable manifold probability patterns

Experimental data shows deviations in compressibility predictions

Highlights surface flow intermittency and energy cascade effects

Abstract

The small-scale velocity gradient is connected to fundamental properties of turbulence at the large scales. By neglecting the viscous and nonlocal pressure Hessian terms, we derive a restricted Euler model for the turbulent flow along an undeformed free surface and discuss the associated stable/unstable manifolds. The model is compared with the data collected by high-resolution imaging on the free surface of a turbulent water tank with negligible surface waves. The joint probability density function (PDF) of the velocity gradient invariants exhibits a distinct pattern from the one in the bulk. The restricted Euler model captures the enhanced probability along the unstable branch of the manifold and the asymmetry of the joint PDF. Significant deviations between the experiments and the prediction are evident, however, in particular concerning the compressibility of the surface flow. These results highlight the enhanced intermittency of the velocity gradient and the influence of the free surface on the energy cascade.