Information transfer between turbulent boundary layer and porous media

TL;DR

This study uses transfer entropy to analyze the causal interactions between turbulent flow and porous media, revealing how porosity influences the directionality and strength of flow interactions.

Contribution

It introduces a quantitative method using transfer entropy to measure the causal interactions between turbulent flow and porous media based on numerical simulations.

Findings

Porosity significantly affects the interaction intensity and spatial extent.

As porosity increases, flow interactions become dominated by shear-flow instabilities.

Interactions are asymmetric at moderate porosity levels, influenced by near-wall eddies.

Abstract

The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e., causal-and-effect relations, of this interaction. To shed light on the problem, we use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous media using interface-resolved direct numerical simulation. Our results show that the porosity of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface-subsurface interactions. For values of porosity equal to 0.5, top-down and bottom-up interactions strongly are asymmetric, the former being mostly influenced by small near-wall eddies. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.