On the influence of coherent structures on flow hydrodynamics, transport and mixing at river confluences
Event details
| Date | 22.09.2015 |
| Hour | 12:00 › 13:15 |
| Speaker | Dr Georges Constantinescu, IIHR-Hydroscience & Engineering, Civil and Environmental Engineering Dept, The University of Iowa, USA |
| Location | |
| Category | Conferences - Seminars |
Abstract:
River confluences are fundamental components of river networks that play an important role in regulating the movement of sediment through these networks and are habitats of high ecological value. The convergence of flow induced by the configuration, or planform, of the two conjoining channels results in highly three-dimensional patterns of fluid motion. Dynamics of mixing controls how tributary inputs of nutrients and food are dispersed in the main river, downstream of the confluence.
We investigate flow structure and mixing based on Detached Eddy Simulations conducted for several natural river confluences with both a concordant bed and with a high degree of bed discordance, respectively. Additional information on the effects of confluence angle, bed roughness, stratification and channel curvature on the development of the shallow mixing interface (MI) and mixing between the two streams is obtained from simulations conducted in more idealized geometries. We analyze the spatial development of the MI as a function of the main geometrical and flow parameters defining the confluence and how bed friction affects the dynamics of the MI eddies. We also investigate the role played by the large-scale turbulence and, in particular, by the quasi-2D eddies generated within the MI and by the streamwise-oriented vortical (SOV) cells forming in the vicinity of the mixing interface in mixing and sediment entrainment at natural river confluences with a concordant bed. Numerical results show that strongly coherent SOV cells are one of the main mechanisms for the growth of the confluence scour hole. We show that the main reason why SOV cells have a large capacity to entrain sediment is because their cores are subject to large-scale bimodal oscillations toward and away of the mixing interface, which greatly enhances the erosion capacity of these structures.
Short biography:
Dr. Constantinescu is a Professor in the Civil and Environmental Engineering Department at the University of Iowa and a Research Engineer at IIHR-Hydroscience and Engineering. Dr. Constantinescu got his Ph.D. at the University of Iowa in 1998. Following this, he occupied various research positions at Arizona State University and at the Center for Turbulence Research and the Center for Integrated Turbulence Simulations at Stanford University where he worked on the development of novel numerical algorithms for viscous flows on structured and unstructured meshes, Detached Eddy Simulation and computational aero-acoustics. He then joined the University of Iowa as an Assistant Professor in 2004. His research program is based on the use of eddy-resolving simulations to understand the physics of several important classes of environmental and geo-physical flows. Dr. Constantinescu’s current research focuses on applications related to river engineering, flow and transport processes around hydraulic structures, stratified flows and fluid-structure interaction, shallow flows, eco-hydraulics and flow in porous media. Dr. Constantinescu has published over 70 journal papers and 150 conference papers.
River confluences are fundamental components of river networks that play an important role in regulating the movement of sediment through these networks and are habitats of high ecological value. The convergence of flow induced by the configuration, or planform, of the two conjoining channels results in highly three-dimensional patterns of fluid motion. Dynamics of mixing controls how tributary inputs of nutrients and food are dispersed in the main river, downstream of the confluence.
We investigate flow structure and mixing based on Detached Eddy Simulations conducted for several natural river confluences with both a concordant bed and with a high degree of bed discordance, respectively. Additional information on the effects of confluence angle, bed roughness, stratification and channel curvature on the development of the shallow mixing interface (MI) and mixing between the two streams is obtained from simulations conducted in more idealized geometries. We analyze the spatial development of the MI as a function of the main geometrical and flow parameters defining the confluence and how bed friction affects the dynamics of the MI eddies. We also investigate the role played by the large-scale turbulence and, in particular, by the quasi-2D eddies generated within the MI and by the streamwise-oriented vortical (SOV) cells forming in the vicinity of the mixing interface in mixing and sediment entrainment at natural river confluences with a concordant bed. Numerical results show that strongly coherent SOV cells are one of the main mechanisms for the growth of the confluence scour hole. We show that the main reason why SOV cells have a large capacity to entrain sediment is because their cores are subject to large-scale bimodal oscillations toward and away of the mixing interface, which greatly enhances the erosion capacity of these structures.
Short biography:
Dr. Constantinescu is a Professor in the Civil and Environmental Engineering Department at the University of Iowa and a Research Engineer at IIHR-Hydroscience and Engineering. Dr. Constantinescu got his Ph.D. at the University of Iowa in 1998. Following this, he occupied various research positions at Arizona State University and at the Center for Turbulence Research and the Center for Integrated Turbulence Simulations at Stanford University where he worked on the development of novel numerical algorithms for viscous flows on structured and unstructured meshes, Detached Eddy Simulation and computational aero-acoustics. He then joined the University of Iowa as an Assistant Professor in 2004. His research program is based on the use of eddy-resolving simulations to understand the physics of several important classes of environmental and geo-physical flows. Dr. Constantinescu’s current research focuses on applications related to river engineering, flow and transport processes around hydraulic structures, stratified flows and fluid-structure interaction, shallow flows, eco-hydraulics and flow in porous media. Dr. Constantinescu has published over 70 journal papers and 150 conference papers.
Practical information
- General public
- Free
- This event is internal
Organizer
- EESS - IIE
Contact
- Prof. A. Johny Wüest, APHYS