Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


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Home > News > Thesis defense > Thèses soutenues 2020

Soutenance de thèse ENS de Lyon / ECL

Muhammad Zubair Sheikh

Lundi 21 décembrer 2020 à 10h00, visioconférence

Muhammad Zubair Sheikh

Sedimentation and collision of anisotropic particles in turbulence

How settling crystals in clouds orient influences the reflection of radiations from the sun, as well as the rate of aggregation, determining how fast precipitation particles form. These two processes are crucial to understand the climate. This thesis investigates the orientation of heavy non-spherical particles orient as they settle, and how this orientational dynamics affects their probability of collision in a turbulent flow. As suggested by recent development, the inertia of the fluid surrounding the particle plays a crucial role in determining the torque. We perform numerical simulations to study the settling of ellipsoids, which provide a simple representation of the anisotropy of particles. Our results indicate that anisotropic particles in a turbulent flow settle with a random orientation, or with their broad-side down, depending on the ratio between the settling velocity and the characteristic velocity of the smallest eddies in the flow. We also study the collision rate of oblate ice crystals in clouds, and elucidate the role of turbulence and differential settling in the dynamics of collision between spheroids.

Lien zoom pour la visioconférence:
https://ec-lyon-fr.zoom.us/j/99845495332?pwd=enEwVGQrN1FhMEw0Q2JCMmQwWXkvQT09
Meeting ID: 998 4549 5332
Passcode: 595123

Composition du jury:
Alberto Aliseda : rapporteur
Dario Vincenzi : rapporteur
Elisabeth Guazzelli : examinatrice
Aurore Naso : Examinatrice
Bernhard Mehlig Invité
Fabien Godeferd : Directeur de thèse
Alain Pumir : Co-directeur de thèse

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