Particle Laden Gravity Currents dynamics in highconcentration regimes

<p>LEMTA - UMR 7563 CNRS-UL - Universite de Lorraine, Nancy, France</p><p><br>Particle-laden gravity currents (PLGC) are commonly found in estuaries<br>where rivers discharge suspended matters into the oceans. The dynamics of<br>these stratified flow is largely related to the properties of the suspended particles, such as their geometry, concentration, and particles size. While several<br>studies have focused on low concentration regimes (e.g. [1]), the physical mechanisms controlled by particle size and concentration are largely unknown for<br>volume fraction larger than 2 %.</p><p><br>In order to investigate how the dynamics of PLGC is influenced by particle<br>concentration and particle size in high concentration regimes, we study the impact of different particle sizes ranging from 6µm to 85µm.</p><p><br>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<br>a controlled density. A particular focus is put on hypopycnal freshwater currents with high concentration suspended particles advancing through a heavier<br>environment. We follow the progress of the current with a high frequency CCD<br>camera. Quantitative data can then be determined using optical methods such<br>as Light Attenuation Technique which is extended to multiphase flows.</p><p><br>Different flow regimes are observed depending on the concentration range and<br>particle size. These regimes highlight the competition between advective transport controlled by density difference and convective sedimentation. Indeed four<br>mechanisms are observed in these regimes, respectively horizontal advection at<br>the surface, sedimentation, advection parallel to the tank bottom, and particle<br>rise of due to buoyancy effects of the surrounding fluid.</p><p><br>References<br>[1] Bruce R. Sutherland et al. “Particle settling from constant-flux surface<br>gravity currents and a near-stationary particle-bearing layer”. In: Physical<br>Review Fluids 6.6 (June 10, 2021). Publisher: American Physical Society,<br>p. 063802. doi: 10 . 1103 / PhysRevFluids . 6 . 063802. url: https : / /<br>link . aps . org / doi / 10 . 1103 / PhysRevFluids . 6 . 063802 (visited on<br>10/25/2021)</p>