Investigation of a thin permeable layer effect on turbulent flow and passive scalar transport in a channel

Abstract

Large eddy simulations of turbulent flow and passive scalar transport in a channel partially filled with an array of spherical particles, mimicking a layer of deposited material over a surface, are carried out to investigate the effect of turbulence mixing on the passive scalar transfer rate from the channel wall. It is observed that large turbulence structures generated at the permeable layer-fluid interface penetrate into the porous media and enhance the scalar transport from the channel wall. The small gap between the layer of particles and the wall also induces a channeling effect that implies turbulence mixing and high velocity near the wall resulting in an enhancement in scalar transport from the channel wall. The influence from the distance between the particles in one layer, particle diameter and the gap thickness on the passive scalar transport is also investigated. It is found that the highest Stanton number is derived for the largest distance between particles since this facilitates the motion of the large turbulent structures into the porous layer. Such motions will affect the scalar transport from the channel wall into the bulk. The channeling effect is observed to be the most important parameter when the particle diameter and the gap thickness are varied, and the highest Stanton number is achieved for the cases with the most effective channeling effect.