Laterally confined flows through macro-roughness elements

Problematic issue

The aim is to study the influence of emerged or slightly submerged macro-roughness elements (modelling trees or houses in floodplains) on the structure of laterally confined flows (open-channel with a  single rectangular cross-section).

Scientific issues

  • Variation of the flow structure with the submergence parameter D/h of the macro-roughness elements (D = time-averaged water depth and h = macro-roughness height), for 1<D/h<1.5.
  • Influence of the Froude, Reynolds, and Strouhal numbers on the flow structure
  • Influence of the streamwise flow  non-uniformity on the flow structure (comparison  uniform flow / accelerated flow)
  • Influence of a longitudinal transition of hydraulic roughness on the flow structure.
  • Influence of the bed roughness (smooth bottom vs. rough bottom) on the flow structure.
  • Influence of unsteadiness on the flow structure.

Methodology

The experiments are conducted in an 18m x 3m  flume, but using only one third of the width (18m x 1m). 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 bed (glass)
  • Tree models (wooden cylinders 1 cm in diameter) placed on a rough bed (dense artificial grass). Tree density: 81 trees/m², with a staggered distribution.
  • House models (6.4 cm side PVC cubes) placed on a rough bed (dense artificial grass). Density of houses: 49 houses/m².

The velocity field is measured using an ADV (side-looking probe) or  PIV 2D-2C (vertical-longitudinal plane). These flows are also  numerically modeled with 2D and 3D industrial or research codes.

Projects

  • ANR FlowRes  project (2015-2018). ‘Predicting flows in floodplains with evolving land use during extreme flood events’.

Partners

  • École Nationale Polytechnique d’Alger (ENPA)
  • Laboratoire d’Hydraulique Saint-Venant (LHSV)
  • National Institute of Technology (NIT) in Rourkela, India.

PhD theses and post-doctorates

  • January 2013 – June 2016: PhD of Victor Dupuis entitled : ‘Experimental investigation of flows subjected to a longitudinal transition in hydraulic roughness in single and compound channels’. PhD Université de Lyon, École Doctorale ED162. Co-supervised by S. Proust, C. Berni, and A. Paquier (director)
  • 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.
  • PhD of Djnana Khuntia (2016-2020) entitled ‘Unsteady open-channel flows over a rough-bed with and without emergent rigid vegetation’, National Institute of Technology, Rourkela. Supervised by K. Khatua and S. Proust from March to September 2018.

Publications