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Soutenance de Sheikh Muhammad Zubair

Sedimentation and collision of anisotropic particles in turbulence
When Dec 21, 2020
from 10:00 to 12:00
Where Visioconférence
Contact Name Sheikh Muhammad Zubair
Attendees Sheikh Muhammad Zubair
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The thesis is jointly supervised by Alain Pumir (ENSL) and by Fabien Godeferd (ECL).

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.