Particle coherent structures in incompressible fluid flows
The motion of small particles in incompressible steady flows can be strongly characterized by the creation of particle attractors. Several dissipative mechanisms may lead to the accumulation of particles, such as inertial forces due to the particle-fluid density mismatch or to finite-size effects in the bulk. Other dissipative effects which may lead to attractors are due to gravity and Basset history forces. The particle accumulation mechanism of interest in this talk relies on the interaction of the particles with undeformable boundaries, very frequent in boundary-driven flows. For dilute suspensions, these accumulation phenomena are successfully modeled as single-particle attractions and are strongly correlated to the topology of the fluid flow without particles. When the accumulations are in form of periodic or quasi-periodic patterns, they are termed finite-size Lagrangian coherent structures, since they are the result of the Lagrangian topology of the fluid flow and of the finite-size effect of the particle near the boundary. Boundary-driven flows will be considered to demonstrate the relative importance of the several dissipation mechanisms which affect the particle motion. A comparison between numerical simulations and experiments will be presented to further strengthen the theoretical understanding of finite-size Lagrangian coherent structures.