Direct effects of boundary permeability on turbulent flows: observations from an experimental study using zero-mean-shear turbulence

Mark W Mccorquodale,R.J Munro

doi:10.1017/jfm.2021.160

Abstract

Highlights

Turbulence interacting with a boundary is a fundamental topic of interest for scientists working within a broad range of fields. [Here we use the term ‘boundary’ to refer to the plane separating an impermeable surface, or the surface of a porous media, and an adjacent layer of fluid]
For each experiment reported here, data describing the statistical structure of the mean and turbulent components of the flow above the boundary-effected region were in good agreement with the above description of the flow. [We note that representative results describing the structure of the flow produced by the apparatus have been reported previously by McCorquodale & Munro (2017) and McCorquodale & Munro (2018b).] here we focus on reporting results within the boundary-effected region of the flow, which, recall, we define as the thin layer of height δs above the permeable boundary over which the degree of isotropy w/u departs from a value of 1 and decreases as the boundary is approached
The results indicate that when ReK 0.2 the boundary acts as if it were impermeable. In this case the interaction is dominated by the blocking of a far-field turbulent kinetic energy (TKE) flux by the kinematic blocking condition (McCorquodale & Munro 2017), with secondary mechanisms acting through intercomponent energy transfers (Perot & Moin 1995; Walker et al 1996; McCorquodale & Munro 2018a)

Summary

Introduction

Turbulence interacting with a boundary is a fundamental topic of interest for scientists working within a broad range of fields. [Here we use the term ‘boundary’ to refer to the plane separating an impermeable surface, or the surface of a porous media, and an adjacent layer of fluid]. Much research has been devoted to understanding the interaction of a turbulent flow with a flat (smooth or rough) impermeable surface aligned with the plane of the boundary parallel to the mean velocity of the flow, which we refer to as turbulent channel flow. Many natural and engineering materials are permeable, and the structure of the TBL adjacent to the surface of a porous media is of great interest. In this case, the canonical problem consists of turbulent channel flow in which a permeable media is bounded on (at least) one side by a turbulent flow. Recent studies have significantly improved our understanding of this flow and reveal the breadth of related problems, with applications as diverse as monitoring and improving water quality in streams and coastal regions (Manes et al 2009; Voermans et al 2017); improving the efficiency of engineering devices used for heat and mass transfer, such as catalytic converters and heat exchangers (Kuwata & Suga 2017); and the design of novel surfaces for drag reduction purposes (Rosti et al 2018)

Methods

Findings

Discussion

Conclusion