Special Issue on “Transport Phenomena at the Interface Between Fluid and Porous Domains”

Abstract

Free flow above permeable domains is a common problem in both natural and industrial environments. The classical problem of turbulent flows above forests and urban areas, known as the canopy flow problem (Finnigan 2000), was addressed by hundreds of publications. A library search for the keywords ‘canopy and flow’ in the ISI database returned 1312 results in April 2007 and 1845 results in April 2009, about 40% increase in the last 2years alone. In fact, this search underestimates the actual number of publications since research of flow above permeable domains covers a much wider range of scenarios. Vegetated flows in rivers and wetlands, flow above gravel streambeds, and flow above coral reefs are a few environmental examples; industrial examples include flows in coating processes, chemical reactors, and electronic cooling; and examples of a much smaller length scale include flows above bio-films and inside bio-tissues. Studies of flows over permeable domains include both laminar and turbulent flow regimes. Where most of the porous media studies focus on laminar and creeping flows, terrestrial, ocean, and atmospheric flows are all turbulent. Combinations such as turbulent channel flows above laminar flow inside dense gravel beds are also common. Most of the past and present research activities are often classified by the following four disciplines: porous media flows (e.g., Whitaker 1999), atmospheric canopy flows (e.g., Finnigan 2000), vegetated flow (e.g., Nepf 1999), and fluvial flows. Studies of fluvial flows were recently addressed in a special issue on double averaging applications (Nikora and Rowinski 2008). The following special issue with its 13 publications covers both laminar and turbulent flow regimes while emphasizing on fundamental questions of formulating the transport conditions at the interface between the fluid and the porous domains. The most famous publication on laminar flows above porous interfaces is the study by Beavers and Joseph (1967) (cited 771 times, ISI, April 2009). By investigating the flow above porous domains, they developed a linear relationship between the velocity gradient above the interface and the interface slip velocity. However, numerous studies showed that the Beavers and Joseph condition is not general enough and a coupled solution of both the free flow and