Levitation—the rising or hovering of an object in apparent defiance of gravity—is a captivating phenomenon with a wide range of applications. In this visualization, we demonstrate our newly discovered form of fluid dynamical levitation of small particles that may be 10, 100, or even 1000 times as dense as the fluid. The transport of small particles such as sediment, droplets, or microorganisms commonly occurs in natural and industrial flows. However, the transport process is still not well understood when the inertia of the particles is non-negligible. In this case, the particles are not restricted to following the streamlines of the flow, and therefore can have trajectories that are far more complex than the motion of the fluid. In this work, we illustrate a counter-intuitive consequence of the particles having inertia by showing that the dynamics of interacting vortices can trap heavy particles and carry them in a direction directly opposite to the direction of the flow and to the force of gravity. We expect our work to contribute to a better understanding of natural phenomena such as the transport of ocean sediment and sea sprays as well as to applications like particle sorting. This visualization was produced by rigorous simulations of the Navier-Stokes equations based on our theoretical predictions of this phenomenon.
This video first shows the upward motion of a system of four vortices against a downward flow stream. Light blue particles are then placed within the flow with the force of gravity acting on the particles in the downward direction. While some of the particles are swept downstream, a subset of them become trapped in the motion of the vortices and are carried upstream, or levitated. These trapped particles cluster together at the labeled attracting points. To visualize the initial positions of the subset of particles that become trapped and levitated, the particles are colored according to which attracting point they migrate to. The orange and green colors illustrate the fractal pattern of the initial positions of the trapped particles. Finally, the visualization shows the migration of those particles to their respective attracting points.