Double Averaging Analysis Applied to a Large Eddy Simulation of Coupled Turbulent Overlying and Porewater Flow
Lian Y.P. Dallmann J. Sonin B. Roche K.R. Packman A.I. Liu W.K. Wagner G.J.
November 2021John Wiley and Sons Inc
Water Resources Research
2021#57Issue 11
Freestream turbulence in rivers is a key contributor to the flux of dissolved nutrients, carbon, and other ecologically important solutes into porewater. To advance understanding of turbulent hyporheic exchange and porewater transport, we investigate flow over and through a rough bed of spheres using large eddy simulation (LES). We apply double averaging (combined space and time averaging) to the LES results to determine the mean velocity distribution, momentum balance, and drag forces. Our simulations show large-scale freestream structures interacting strongly with vortices generated at the surfaces of individual spheres to control turbulent momentum fluxes into the bed. The transition between turbulent flow and Darcy flow occurs over the first row of spheres, where turbulence decays rapidly and turbulent kinetic energy, Reynolds stress, and drag forces peak. Below this region, turbulence is only present in the high-velocity flow in open pore throats. Experimental observations suggest that minimum mean porewater velocity occurs in the first open pore space below the transition region, but our results show that the minimum occurs between the first and second pore spaces. The simulation mean porewater velocities are approximately half those captured in measurements because the model resolves the entire flow continuum while measurements can access high-velocity fluid in open pores. The high-resolution dual time-space averaging of the LES resolves both turbulent and mean flow features that are important to interfacial solute and particle fluxes, providing a means to include turbulent hyporheic exchange in upscaled river models, which has not been achieved to date.
hyporheic zone , large eddy simulation , sediment-water interface , turbulent flow
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Institute of Advanced Structure Technology and State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, China
Department of Mechanical Engineering, Northwestern University, Evanston, IL, United States
Center for Preparatory Studies, Nazarbayev University, Nur-Sultan, Kazakhstan
Department of Civil Engineering, Boise State University, Boise, ID, United States
Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL, United States
Institute of Advanced Structure Technology and State Key Laboratory of Explosion Science and Technology
Department of Mechanical Engineering
Center for Preparatory Studies
Department of Civil Engineering
Department of Civil and Environmental Engineering
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