The aim is to study the transverse and longitudinal free surface waves (seiche or seiching phenomenon) induced by vortex shedding behind emerged or slightly immersed macro-roughnesses in laterally confined flows. Macro-roughnesses represent tree or house models.
- Quantification of the seiche phenomenon (transverse and longitudinal oscillations of the free surface) for emerged macro-roughness elements (D/h<1, with D = time averaged water depth and h = macro-roughness height) and/or slightly submerged elements (1<D/h<1.5).
- Influence of key dimensionless numbers: submergence D/h, Froude number based on water height, Reynolds and Strouhal numbers based on the macro-roughness elemnt width.
- Influence of the streamwise flow non-uniformity on the seiche phenomenon.
- Influence of the bed roughness (smooth bottom vs. rough bottom) on the seiche phenomenon
- Influence of the free surface oscillations on the time-averaged velocity and on turbulence statistics.
The experiments are conducted in the 18m x 3m channel of Irstea, but using only one third of the width. The cross-section is rectangular, the side walls are made of glass. For the bottom, different hydraulic roughnesses are studied:
- Tree models (wooden cylinders 1 cm in diameter) placed on a smooth bottom (glass)
- Tree models (wooden cylinders 1 cm in diameter) placed on a rough bottom (dense artificial grass). Tree density: 81 trees/m², with a staggered distribution.
- House models (6.4 cm side PVC cubes) placed on a rough bottom (dense artificial grass). Density of houses: 49 houses/m².
Water level fluctuations are measured using ultrasonic sensors.
These flows were also numerically modelled with 2D and 3D industrial or research codes.
Channel 18m x 1 m, with (1) cylindrical roughness elements (tree models) emerged on a rough bottom (meadow model) and (2) cubic roughness elements (house models) emerged on a rough bottom (meadow model).
Projet ANR FlowRes (2015-2018). ‘Prédire les écoulements dans les plaines d’inondation dont l’occupation du sol varie, lors de crues extrêmes’.
- École Nationale Polytechnique d’Alger (ENPA)
- Laboratoire d’Hydraulique Saint-Venant (LHSV)
PhD theses and post-doctorate
- PhD of Meriem Chétibi (January 2016 – December 2019) entitled : ‘Turbulent flows in non-prismatic open-channels’ (co-directors : S. Benmamar, ENPA; S. Proust, Irstea)
- PhD of Marina Oukacine (January 2016 – Juin 2019): ‘Experimental and numerical study of flows through emerged and slightly submerged macro-roughness elements’. Co-directors: N. Goutal (EDF), et S. Proust.
- Post-doctorate of Marc Chatelain (March 2017 – august 2018) entitled ‘3D LES (Large Eddy Simulation) of flooplain flows in the presence of emergent and slightly submerged macro-roughness elements’. Supervised by S. Proust.
Example of result
Longitudinal profiles of the standard deviation of water level fluctuations σ (normalised by the time-averaged flow depth D) and of the submergence D/h, where h = height of a macro-roughness element (Chetibi et al. 2019)
- Chetibi, M., Proust, S., Benmamar, S. (2019 ). Transverse surface waves in steady uniform and non-uniform flows through emergent and weakly submerged square cylinders. Journal of Hydraulic Research, DOI: 10.1080/00221686.2019.1647885
- Chatelain, M., and S. Proust (2019). “Flows through emergent rigid vegetation: effects of bed roughness and vertical confinement on flow structure and surface waves”. In preparation.
- Dupuis, V., S. Proust, C. Berni, and A. Paquier (2016). Combined effects of bed friction and emergent cylinder drag in open channel flow, Environmental Fluid Mechanics, vol. 16, n° 6, p. 1173-1193, DOI: 10.1007/s10652-016-9471-2.