Journal article
Numerical evaluation of the effects of planform geometry and inflow conditions on flow, turbulence structure, and bed shear velocity at a stream confluence with a concordant bed
Journal of Geophysical Research: Earth Surface, Vol.119(10), pp.2079-2097
10/2014
DOI: 10.1002/2014JF003244
Abstract
This study numerically investigates the effects of variations in inflow conditions and planform geometry on large‐scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology. Several numerical experiments are conducted in which either the Kelvin‐Helmholtz mode or the wake mode dominates within the mixing interface (MI) between the two confluent streams as the junction angle and alignments of the tributaries are altered. In the Kelvin‐Helmholtz mode, the MI contains mostly corotating vortices driven by the mean transverse shear across the MI, while in the wake mode the MI contains counterrotating vortices forming by the interaction of the separated shear layers on the two sides of a zone of stagnant fluid near the junction corner. A large angle between the two incoming streams is not necessary for the development of strongly coherent streamwise‐oriented vortical (SOV) cells in the immediate vicinity of the MI. Results show that such SOV cells can develop and produce high bed friction velocities even for cases with a low angle between the two tributaries and for cases where the downstream channel is approximately aligned with the axes of the two tributaries (low‐curvature cases). SOV cells tend not to develop only when the incoming streams are parallel and aligned with the downstream channel (junction angle of zero), and the incoming flows produce a strong Kelvin‐Helmholtz mode. Under such conditions, quasi 2‐D MI vortices play the primary role in mixing and the production of high bed shear velocities. Simulations with and without natural bed morphology/local bank line irregularities indicate that planform geometry and inflow conditions primarily govern the development of coherent flow structures, but that bathymetric and bank line effects can locally modify details of these structures.
Key Points
Tributary angle influence flow and turbulence structure at confluencesSOV cells can form even at confluences with a small angleMixing interface can change from wake mode to KH mode
Details
- Title: Subtitle
- Numerical evaluation of the effects of planform geometry and inflow conditions on flow, turbulence structure, and bed shear velocity at a stream confluence with a concordant bed
- Creators
- George Constantinescu - University of IowaShinjiro Miyawaki - University of IowaBruce Rhoads - University of Illinois at Urbana‐ChampaignAlexander Sukhodolov - Institute of Freshwater Ecology and Inland Fisheries
- Resource Type
- Journal article
- Publication Details
- Journal of Geophysical Research: Earth Surface, Vol.119(10), pp.2079-2097
- DOI
- 10.1002/2014JF003244
- ISSN
- 2169-9003
- eISSN
- 2169-9011
- Number of pages
- 19
- Language
- English
- Date published
- 10/2014
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9983992037402771
Metrics
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