A turbulent flow overlying a permeable wall can be subdivided into two distinct flow regions separated by a permeable interface. The first is the surface (or free) flow region, which overlies the interface. The second is the subsurface (or pore) flow region, which occurs within the permeable wall. While the near-wall surface flow can be turbulent, deep within the subsurface flow is often laminar and can be described by Darcy’s law (a balance of viscous and pressure forces). Thus, a region must exist between these two extremes where the flow undergoes a transition from inertia-dominated turbulence to viscous-dominated, laminar flow across the permeable interface. Such region, typically termed the ‘transitional layer’ develops across the permeable interface where non-linear flow interactions between the free flow and the pore flow take place. The very existence of the transitional region and the unique nature of these interaction may explain previously observed modification of the turbulent structure of the free flow, as compared to a classical turbulent boundary layer (TBL). The goal of this study is to explore the role of wall permeability and surface topography in flow interactions across a permeable interface and the corresponding TBL modifications in the surface flow region. The current work experimentally investigates the turbulent flow overlying impermeable and permeable walls with identical surface topography. This study was conducted using particle image velocimetry (PIV) measurements in a refractive index matching (RIM) environment to obtain full optical access to the flow in the vicinity of the permeable interface. Utilizing velocity statistics and conditional averaging, quantitative assessments were made for the TBL modification imposed by permeability and topography as well as the mutual interplay between the surface and subsurface flows. In addition, the obtained PIV data suggests the existence of an amplitude modulation phenomenon of the subsurface flow by the free flow as has been previously observed in impermeable TBLs.
About the Speaker
Taehoon Kim is a PhD candidate in Theoretical and Applied Mechanics in the Department of Mechanical Science and Engineering and is advised by Dr. Kenneth Christensen at the University of Notre Dame. He received B.S. in Mechanical Engineering at Hanyang University, Seoul, South Korea in 2011 and M.S. in TAM at the University of Illinois, Urbana-Champaign. He is a recipient of fellowship in 2012 from Korean Energy Technology Evaluation and Planning, Seoul. His research focuses on the flow interaction induced by various flow systems, which are often encountered in environmental and geophysical context, utilizing laser-based measurement techniques.
Host: Professor Mattia Gazzola