MSc project: Structure and dynamics of turbulence in wall-bounded shear flow over a highly permeable wall

MSc student: Mehdi Niazi Ardekani

Project supervisors: Dr. ir. W.-P. Breugem, Dr. ir. G.E. Elsinga

Project start: November 2013

Project description:
Porous materials with high external surface area are employed in a variety of industrial applications such as catalytic converters, fuel cells and heat exchangers. The permeability (or the ability to transmit fluid across the pores) of such materials has a strong influence on the turbulent flow along these materials and hence the efficiency of heat and mass transfer in these applications.

In recent years just a few experimental and numerical studies have been performed on turbulent flows over permeable walls. From these studies it was found that the skin friction is enhanced with respect to impermeable walls with a similar surface roughness.  However, flow physics near highly permeable walls is not fully understood yet. More specifically it seems that so-called hairpin vortices are absent near highly permeable walls, contrary to turbulence near solid walls. The aim of this project is to gain understanding of the dominant structures and the self-sustaining mechanisms of turbulence in wall-bounded shear flows over highly permeable walls.

In this project the Volume-Averaged Navier-Stokes (VANS) equations will be used in fully-resolved simulations (DNS) of the turbulent flow over a permeable wall made of ceramic foam. The results will be compared with existing experimental data in literature. Next, a linear stochastic estimation technique will be used to capture the structures of turbulence that contribute most to the Reynolds shear stress. Finally the self-sustainability and auto-generation of the most dominant turbulent structure will be studied.

It is expected that this study will provide a base for further investigations regarding heat and mass transfer across a porous interface.