Particle Laden Gravity Currents dynamics in highconcentration regimes

LEMTA - UMR 7563 CNRS-UL - Universite de Lorraine, Nancy, France

Particle-laden gravity currents (PLGC) are commonly found in estuaries
where rivers discharge suspended matters into the oceans. The dynamics of
these stratified flow is largely related to the properties of the suspended particles, such as their geometry, concentration, and particles size. While several
studies have focused on low concentration regimes (e.g. [1]), the physical mechanisms controlled by particle size and concentration are largely unknown for
volume fraction larger than 2 %.

In order to investigate how the dynamics of PLGC is influenced by particle
concentration and particle size in high concentration regimes, we study the impact of different particle sizes ranging from 6µm to 85µm.

The experimental lock-release device is composed of a tilted tank at a controlled angle in which a particle loaded fluid is released on an environment with
a controlled density. A particular focus is put on hypopycnal freshwater currents with high concentration suspended particles advancing through a heavier
environment. We follow the progress of the current with a high frequency CCD
camera. Quantitative data can then be determined using optical methods such
as Light Attenuation Technique which is extended to multiphase flows.

Different flow regimes are observed depending on the concentration range and
particle size. These regimes highlight the competition between advective transport controlled by density difference and convective sedimentation. Indeed four
mechanisms are observed in these regimes, respectively horizontal advection at
the surface, sedimentation, advection parallel to the tank bottom, and particle
rise of due to buoyancy effects of the surrounding fluid.

References
[1] Bruce R. Sutherland et al. “Particle settling from constant-flux surface
gravity currents and a near-stationary particle-bearing layer”. In: Physical
Review Fluids 6.6 (June 10, 2021). Publisher: American Physical Society,
p. 063802. doi: 10 . 1103 / PhysRevFluids . 6 . 063802. url: https : / /
link . aps . org / doi / 10 . 1103 / PhysRevFluids . 6 . 063802 (visited on
10/25/2021)