Abstract: Solute transport and mixing at channel-flow–porous media interfaces are strongly influenced by velocity and turbulence structures near porous media, and such coupled channel-flow–porous media systems are commonly observed in nature. However, the effects of pore-scale flows on solute transport in the coupled systems are currently unclear. In this study, we combine particle image velocimetry experiments and large eddy simulations to resolve the pore-scale flow characteristics over and within a porous bed. Then, we perform solute transport simulations by coupling the pore-scale flow fields with a particle-tracking model and show that the pore-scale flows inherent to porous media structure control solute transport. Pore-scale flow properties such as preferential downward–upward flows and vortices occurring near the channel-flow–porous media interface are shown to exert dominant control over interfacial mass exchange and solute transport. To clarify the effects of pore-scale flows on reach-scale transport, we conduct macroscale transport modeling with a spatially averaged stream-wise velocity profile. Because the profile-based model does not incorporate important pore-scale flow features, it significantly overestimates mass transfer into the porous bed, thereby exacerbating late-time tailings in breakthrough curves. Finally, a spatial Markov model, a type of upscaled stochastic transport model, is shown to effectively capture the pore-scale interfacial transport mechanisms via a velocity transition matrix. Our findings confirm that solute transport through channel-flow–porous media interfaces is controlled not only by interfacial turbulent-mixing profiles but also by detailed pore-scale flow structures. Article Highlights: We demonstrate the effects of pore-scale flows on solute transport in coupled turbulent channel-flow–porous media systemsPore structure near the interface exerts dominant control over interfacial mass exchange and solute transportSpatial Markov model effectively upscales the effects of pore-scale flows on solute transport.
Bibliographical noteFunding Information:
We thank the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for computational resources and support. J. S. K. and P. K. K. acknowledge a grant from Korea Environment Industry and Technology Institute (KEITI) through Subsurface Environmental Management (SEM) Project (2018002440003), funded by the Korea Ministry of Environment (MOE) and also acknowledge Grant-in-Aid funds through the Office of the vice president for research at the University of Minnesota. J. S. K. and I. W. S. acknowledge the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (Grant 19DPIW-C153746-01).
© 2021, The Author(s), under exclusive licence to Springer Nature B.V.
- Coupled channel-flow–porous media systems
- Pore-scale flow
- Solute transport
- Turbulent mixing