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EXPERIMENTAL STUDY OF TURBULENT STRUCTURE OVER PERMEABLE WALLS WITH A REFRACTIVE-INDEX-MATCHING TECHNIQUE

Taehoon Kim
Department of Mechanical Convergence Engineering, Graduate School of Hanyang University, Seoul 133791, Republic of Korea; Department of Mechanical Science and Engineering University of Illinois at Urbana-Champaign MEB, 1206 W. Green St. Urbana, IL 61801, USA

Gianluca Blois
Department of Aerospace and Mechanical Engineering University of Notre Dame 118 Hessert Lab. Notre Dame, IN 46556, USA

James Best
Depts of Geology, Geography, Mech. Science and Eng., and Ven Te Chow Hydrostems Laboratory University of Illinois at Urbana-Champaign Natural History Building, 1301 West Green Street, Urbana, IL, 61801-2938

Kenneth T. Christensen
Laboratory for Turbulence and Complex Flow Department of Theoretical and Applied Mechanics University of Illinois at Urbana-Champaign, Urbana, IL 61801 USA; Aerospace and Mechanical Engineering; Civil & Environmental Engineering & Earth Sciences University of Notre Dame Notre Dame, Indiana, USA 46556

Sinopsis

High-resolution particle velocimetry (PIV) measurements were conducted to explore turbulent flow overlying idealized permeable walls. The measurements successfully captured the overlying flow as well as the flow within the pore spaces with the specific goal of investigating the flow interactions across the permeable interface. A refractive-index matching (RIM) technique was employed to gain full optical access to the nearwall and subsurface flow and a number of idealized wall models were fabricated by casting acrylic. The permeable walls consisted of two and five layers of cubically packed uniform spheres (d=25.4mm), which provided 48% of porosity. In addition, an impermeable rough wall with identical topography was considered as a baseline of comparison in order to explore the structural modifications imposed by the permeability in the near-wall region. First- and second-order velocity statistics at two specific locations provided a quantitative assessment of such modifications of the local flow. A double-averaging approached (Nikora et al., 2007) allowed investigation of the global representation of the flow and to assess conventional scaling parameters.