Turbulent transport of non-spherical suspended particles : particle shape, size and rotation
Orateur : Evan Variano
Department of Civil and Environmental Engineering, University of California, Berkeley, USA
Résumé : Natural particles suspended in water are often non-spherical. We explore the ways in which particle size and shape affects particle motion, focusing on particle parameters relevant for plankton, sediment aggregates, or autonomous vehicles. We find that shape has only a very weak effect on particle angular velocity, which is a quantity calculated with respect the global reference frame (i.e. east/north/up). If we analyze rotation in a particle’s local frame (i.e. the particle’s principle axes of rotation), then particle shape has a strong effect on rotation. In the local frame, rotation is described by two components : tumbling and spinning. We find that rod-shaped particles spin more than they tumble, and we find that disc-shaped particles tumble more than they spin. These preferential rotations, as well as total angular velocity, decrease with increasing particle size. Such behavior is indicative of how particles respond to the directional influence of vortex tubes in turbulence, and such response has implications for particle motion other than rotation. Understanding particle alignment is relevant for predicting particle-particle collision rates, particle-wall collision rates, and the shear-driven breakup of aggregates. We discuss these briefly in the context of what can be concluded from the rotation data discussed above.
Date et lieu : le Mardi 14 Juin 2016 à 11h00, salle de séminaire IRPHE