Finite-size Lagrangian coherent structures in a two-sided lid-driven cavity

The motion of small, rigid, nearly neutrally buoyant finite-size particles in a two-sided lid-driven cavity is calculated numerically. The rapid accumulation of particles into coherent structures which is observed experimentally is explained on the basis of single-particle one-way-coupled dynamics. Key is the transfer of the particle from regions of the incompressible flow occupied by chaotic streamlines to regions occupied by regular ones. The particle attractors are caused by lubrication forces which repel the particles from the moving boundaries. This mechanism is independent of particle inertia. Therefore, the particulate structures found represent a class of coherent structures which may be called finite-size coherent structures.