Flow structure and large scale turbulence in an open channel bend of strong curvature with flat and deformed bed

Constantinescu, G.
Köken, Mete
Results of Three-Dimensional (3D) Detached Eddy Simulation (DES) are used to discuss changes in flow structure and large-scale turbulence structures in a high-curvature open channel between conditions present at the start (flat bed) and at the end (equilibrium deformed bed) of the erosion-deposition process. The flow in a 193 degrees bend is simulated, for which the ratio between the bend curvature and the channel width is close to 1.3. For these geometrical parameters, the cross-stream secondary flow and anisotropic effects play a crucial role in the redistribution of the streamwise momentum and influence significantly the distribution of the bed shear stress which, in turn, determines the capacity of the flow to entrain sediment. We also investigated changes in the flow and turbulence structure between Reynolds numbers at which most laboratory experiments are conducted and Reynolds numbers that are closer to those encountered in natural small streams. We show that an energetic thin shear layer containing large-scale eddies develops at the interface between the core of high streamwise velocities and the retarded (flat bed case) or recirculating (deformed bed case) fluid moving close to the inner bank. Highly energetic large-scale Streamwise-Oriented Vortices (SOVs) develop close to the inner bank. The strength of the secondary outer bank SOV cell is enhanced as the Reynolds number is increased. Results show that an increase in Reynolds number by about one order of magnitude enhances significantly the turbulence, the secondary flow, the SOVs, the bed shear stresses and the flow's potential to erode the boundaries.


Coherent structures in a sharply curved bend with and without a spur dike.
Köken, Mete; Budak, Ezgi (null; 2017-08-18)
: Results of three-dimensional (3D) Detached Eddy Simulation (DES) are used to investigate the changes in flow and large-scale coherent structures within a high-curvature open channel, with and without an isolated spur dike located on the outer bank of the
Hydrodynamic processes, sediment erosion mechanisms, and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry
Köken, Mete; Blanckaert, Koen (2013-12-01)
Sharply curved open channel flow with a flat bed is investigated with eddy-resolving numerical simulations that complement laboratory experiments. The focus is on the role of coherent flow structures, how these structures contribute to shear stresses and the capacity of the flow to pick up sediment at the boundaries, and on changes resulting from increasing the Reynolds number between typical values for laboratory model studies and for field conditions. In sharply curved bends, secondary flow leads to a tra...
Coherent structures at different contraction ratios caused by two spill-through abutments
Köken, Mete (Informa UK Limited, 2017-8-23)
Detached eddy simulation (DES) at a channel Reynolds number of 45,000 is used to investigate the coherent structures forming around spill-through abutments located at opposite sides of a rectangular channel which contract the flow section. Changes in the coherent structures are investigated for two contraction ratios at two different scour stages. It is observed that at the small contraction ratio the coherent structures forming around the abutments are similar to the ones observed for isolated abutments. H...
Earthquake stresses and effective damping in concrete gravity dams
Akpinar, Ugur; Binici, Barış; Arıcı, Yalın (2014-03-01)
Dynamic analyses for a suite of ground of motions were conducted on concrete gravity dam sections to examine the earthquake induced stresses and effective damping. For this purpose, frequency domain methods that rigorously incorporate dam-reservoir-foundation interaction and time domain methods with approximate hydrodynamic foundation interaction effects were employed. The maximum principal tensile stresses and their distribution at the dam base, which are important parameters for concrete dam design, were ...
A DES Study for the Role of Contraction Ratio on the Coherent Structures Caused by Two Spill Through Abutments
Köken, Mete (2013-09-13)
Detached Eddy Simulation (DES) is used to investigate the changes in the horseshoe vortex system and the bed shear stress distribution forming around the base of spill-through bridge abutments located at two sides of the channel for two different contraction ratios. DES is conducted at a channel Reynolds number of 45,000, and the incoming flow was fully turbulent that contains resolved turbulence fluctuations. Simulations are conducted at flat bed conditions representing the initiation of the scour process....
Citation Formats
G. Constantinescu and M. Köken, “Flow structure and large scale turbulence in an open channel bend of strong curvature with flat and deformed bed,” 2014, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/55593.