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Effects of Roughness Reynolds Number on Scalar Transfer Mechanisms at the Sediment‐Water Interface
Author(s) -
He G. J.,
Han X.,
Fang H. W.,
Reible D.,
Huang L.
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr024493
Subject(s) - turbulence , scalar (mathematics) , sediment transport , surface finish , mechanics , large eddy simulation , reynolds number , permeability (electromagnetism) , hydraulic roughness , bedform , molecular diffusion , turbulent diffusion , geology , sediment , geotechnical engineering , materials science , geometry , geomorphology , physics , chemistry , engineering , mathematics , biochemistry , membrane , composite material , metric (unit) , operations management
Abstract The passive scalar transport across a sediment‐water interface (SWI) is of fundamental importance to river environments. A model for scalar transfer from water to organic sediment bed is developed. The bed is formed by packed particles so that combined effect of permeability and roughness can be considered. Large‐eddy simulation is used to get spatial and temporal information. The numerical results are compared to data from laboratory experiments, which stress the importance of considering bed roughness to better characterize the turbulent diffusion across the SWI. From the smooth regime to the transitionally regime, the turbulent diffusion exceeds the molecular diffusion and the dominating role at the interface changes from molecular diffusion to turbulent diffusion. In the completely rough regime, the molecular diffusive flux can be ignored compared with the turbulent flux. Moreover, turbulent Schmidt number is found to be higher near the SWI and lower around the middle of flow depth, ranging from 0.5 to 1. The results will be helpful to design the parameterization for the scalar transport over streams, rivers, or coastal areas where flow near the bed surface is relatively high and hyporheic exchange is affected by roughness and bed permeability.