Creëlle, Stéphan

De Mulder, Tom

Mignot, Emmanuel

Schindfessel, Laurent

Ghent University Academic Bibliography

Geophysical Research AbstractsVol. 19, EGU2017-18728, 2017EGU General Assembly 2017© Author(s) 2017. CC Attribution 3.0 License.Experimental study of the free surface velocity field in an asymmetricalconfluenceStephan Creelle (1), Emmanuel Mignot (2), Laurent Schindfessel (1), and Tom De Mulder (1)(1) Hydraulics Laboratory , Department of Civil Engineering, Ghent University, Ghent, Belgium, (2) LMFA, CNRS Universitéde Lyon, INSA de Lyon, Villeurbanne Cedex , FranceThe hydrodynamic behavior of open channel confluences is highly complex because of the combination of dif-ferent processes that interact with each other. To gain further insights in how the velocity uniformization betweenthe upstream channels and the downstream channel is proceeding, experiments are performed in a large scale 90degree angled concrete confluence flume with a chamfered rectangular cross-section and a width of 0.98m. The di-mensions and lay-out of the flume are representative for a prototype scale confluence in e.g. drainage and irrigationsystems. In this type of engineered channels with sharp corners the separation zone is very large and thus the veloc-ity difference between the most contracted section and the separation zone is pronounced. With the help of surfaceparticle tracking velocimetry the velocity field is recorded from upstream of the confluence to a significant dis-tance downstream of the confluence. The resulting data allow to analyze the evolution of the incoming flows (witha developed velocity profile) that interact with the stagnation zone and each other, causing a shear layer betweenthe two bulk flows. Close observation of the velocity field near the stagnation zone shows that there are actuallytwo shear layers in the vicinity of the upstream corner. Furthermore, the data reveals that the shear layer observedmore downstream between the two incoming flows is actually one of the two shear layers next to the stagnationzone that continues, while the other shear layer ceases to exist. The extensive measurement domain also allows tostudy the shear layer between the contracted section and the separation zone. The shear layers of the stagnationzone between the incoming flows and the one between the contracted flow and separation zone are localized andparameters such as the maximum gradient, velocity difference and width of the shear layer are calculated. Analysisof these data shows that the shear layer between the incoming flows disappears quite quickly, because of the severeflow contraction that aids the flow uniformization. This is also accelerated because of a flow redistribution processthat starts already upstream of the confluence, resulting in a lower than expected velocity difference over the shearlayer between the bulk of the incoming flows. In contrast, the shear layer between the contracted section and theseparation zone proves to be of a significantly higher order of magnitude, with large turbulent structures appearingthat get transported far downstream. In conclusion, the resulting understanding of this analysis of velocity fieldswith a larger field of view shows that when analyzing confluence hydrodynamics, one should pay ample attentionto analyze data far enough up and downstream to assess all the relevant processes.

Experimental study of the free surface velocity field in an asymmetrical confluence

https://biblio.ugent.be/publication/8537320/file/8537325

Experimental study of the free surface velocity field in an asymmetrical confluence

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