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Accueil > Actualités > Séminaires > Séminaires 2022

Mardi 22 Novembre 11h00 - LEGI Salle K118

Aurore Naso, LMFA

The role of fluid inertia on the orientation of settling anisotropic particles - Application to cloud microphysics

Understanding the angular dynamics of non-spherical particles in turbulent flows is a challenging fundamental problem, significantly complicated when the particles are denser than the surrounding fluid. However, the settling of anisotropic particles in a flow is of importance in many geophysical and engineering problems, including cloud microphysics. Over a range of temperatures, ice crystals in clouds are indeed shaped like plates.

It will be first shown that fluid inertia plays an important role in the orientation of such objects, despite their small size. I will introduce a parameter allowing to distinguish the regimes in which the particles orientation is essentially driven by the inertial torque (and therefore preferentially horizontal) and those in which the viscous torque prevails. Expressions of the inertial torque available in the literature will be confronted with experimental results.

I will then present the results of numerical simulations of settling ice crystals in turbulent clouds. Their degree of alignment will be characterized as a function of their properties and of turbulence intensity. The collisions between crystals (an important step in the formation of snow aggregates) will be finally investigated. It will be shown that the collision rates can be understood as resulting from three main physical mechanisms : turbulent velocity gradients, differential settling, and particle inertia.

Contact Nathanael Machicoane for more information or to schedule a discussion with the seminar speaker.