Séminaire exceptionnel IUSTI – 30 mai 2023 – 11h salle 259

Sedimenting anisotropic particles – roles of asymmetry, turbulence and waves

Anubhab Roy – IT Madras, Inde

Sedimentation of non-spherical particles occurs in many natural situations and has important consequences for various engineering applications. The orientation of non-spherical sedimenting particles influences the sedimentation rate, the presence or absence of horizontal drift and the scattering of light from particle suspensions. The development of accurate models for the forces acting on fibres moving through fluids has long been a central problem in fluid mechanics. Stokes (1851) considered the drag on an infinite cylinder in the paper in which he introduced his viscous drag law, but it was not until 60 years later, with the work of Oseen (1910) and Lamb (1911), that an accurate model was developed. Extensive efforts to observe and model forces on cylinders with finite length developed slowly until slender-body theory was formalized by Batchelor (1970) and Cox (1970). In this talk, I will discuss fluid inertia’s effects on the fibers’ settling motion. The role of the inertial torque (Khayat & Cox 1989) is used to explain two experimental observations – a symmetry-breaking orientational transition in sedimenting asymmetric fibers and the orientation distribution of symmetric fibers settling in a turbulent flow.