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Stratification Effects on Flow Hydrodynamics and Mixing at a Confluence With a Highly Discordant Bed and a Relatively Low Velocity Ratio
Author(s) -
Cheng Zhengyang,
Constantinescu George
Publication year - 2018
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 - 10.1029/2017wr022292
Subject(s) - confluence , eddy , stratification (seeds) , richardson number , mechanics , secondary circulation , stratified flow , geology , mixing (physics) , flow velocity , flow (mathematics) , large eddy simulation , geometry , physics , turbulence , mathematics , seed dormancy , germination , botany , quantum mechanics , dormancy , computer science , biology , programming language
The effects of temperature induced stratification on flow hydrodynamics, thermal mixing, and the capacity of the flow to entrain sediment at a medium‐size stream confluence with a highly discordant bed are investigated. To isolate the effects due to differences in the temperature/density of the incoming streams, two simulations were conducted with identical flow conditions (mean velocity ratio = 0.41 and temperature difference between the two streams Δ T = 4.7°C). In the first case the Richardson number was Ri = 0 (no coupling between the temperature and the momentum equations via the Boussinesq approximation), while in the second simulation Ri = 0.67. Even in the Ri = 0 case the structure of the mixing interface (MI) was different from the one expected for concordant bed confluences with a similar confluence angle and velocity ratio. The MI contained only corotating eddies shed in the shear layer forming on the fast‐speed side of the confluence apex. In the Ri = 0.67 case no wake region was present but a large recirculation eddy formed not far from the confluence apex. In both cases, the flow near the upstream part of the MI was found to be highly 3‐D and to allow the passage of particles from one side of the confluence to the other. While in the Ri = 0 case mixing was driven by the MI eddies, in the Ri = 0.67 case mixing was controlled by large near‐bed intrusions of heavier fluid from the tributary containing colder water and also by the fluid advected in and out of the recirculation eddy.