LEGI - UMR 5519

The transport of solid particles by a turbulent fluid flow is a complex situation ubiquitous in many geophysical and industrial flows. In geophysics, sediment transport controls the morphological process in rivers, estuaries and coastal oceans. In the context of global warming, human and material risks related to extreme events such as flood in rivers, storm surge at coasts or landslides are likely to increase in the future. A better evaluation and prediction of their impacts and the development of adaptation strategies depend on our ability to predict the fluxes of sediments. The modeling of the complex underlying transport processes strongly depend on the degree of our physical understanding of fine scale processes that remains a challenge for fundamental research. With the recent advances made in basic granular and turbulence physics, high-resolution flow measurement and high-performance computing, new insights into sediment transport physics can be expected over the next decade.

At LEGI, we have developed a specific laboratory sheet flow experiment using coarse lightweight plastic sediments (T. Revil-Baudard PhD, see movie 1).

High speed camera movie of a sheet-flow experiment in the LEGI tilting flume. Speed reduced 8 times (PhD Revil-Baudard, 2014 - DGA)

The Acoustic Concentration Velocity Profiler (ACVP, Hurther et al., 2011) to provide collocated and synchronized velocity and concentration profiles at high spatial and temporal resolutions allowing to estimate second order turbulence statistics (see figure 1).

Figure 1: Measurements and results of two-phase simulations for sheet-flow, from left to right: speed, concentration and Reynolds stress.

Using, this dataset we have developed and tested the first Eulerian-Eulerian two-phase flow LES for sheet-flow (Z. Cheng PhD, see movie 2 and figure 1).

LES simulation of sheet-flow performed using sedFOAM (PhD Z. Cheng, 2016- ONR/NSF)

The LES model results allows to better understand the physical origin of turbulence damping and enhanced turbulent-particle dispersion. This work illustrates how the synergies between experiments, modeling and simulations can bring new insights into fundamental sediment transport processes.

These research activities will be continued within the two on-going PhD work of H. Guta (2019-) and A. Mathieu (2018-).

LES simulation of dilute suspended-load performed using sedFOAM (PhD A. Mathieu, on-going- DGA/SHOM MEPELS)

Funding:
  COOPERA/bourse CMIRA région ARA (2015-2017) – PI J. Chauchat
  Projet INSU LEFE/EC2CO MODSED (2015-2017) – PI J. Chauchat
  HYDRALAB+ JRA Complex (2015-2019) – PI D. Hurther
  ANR JCJC SHEETFLOW (2018-2022) – PI J. Chauchat

PhD students and Postdocs
  Thèse T. Revil-Baudard (DGA 2011-2014)
  Postdoc T. Revil-Baudard (Labex TEC21 2017-2018)
  Thèse de Z. Cheng (ONR/NSF 2011-2016) – collab. Prof. T.-J. Hsu (Univ. Delaware, USA)
  Thèse de A. Mathieu (DGA/SHOM MEPELS 2018-) – collab. Prof. T.-J. Hsu (Univ. Delaware, USA)
  Thèse H. Guta (France-Mozambique grant & ANR JCJC SHEET FLOW 2019-)

References:
Revil-Baudard et al., 2015, 2016
Cheng et al., 2018a, 2018b