# Levitation of heavy particles against gravity in asymptotically downward flows

## TL;DR

This paper demonstrates that heavy particles can be levitated against gravity in downward flows through vortex interactions, challenging the expectation that particles follow the flow direction.

## Contribution

The study introduces a new theory showing heavy particles can be lifted by vortices in downward flows, supported by analytical and simulation results.

## Key findings

- Heavy particles can be levitated against gravity in downward flows.
- Vortex interactions enable particles to move contrary to flow direction.
- The effect has implications for water droplet transport and sediment lifting.

## Abstract

In the fluid transport of particles, it is generally expected that heavy particles carried by a laminar fluid flow moving downward will also move downward. We establish a theory to show, however, that particles can be dynamically levitated and lifted by interacting vortices in such flows, thereby moving against gravity and the asymptotic direction of the flow, even when they are orders of magnitude denser than the fluid. The particle levitation is rigorously demonstrated for potential flows and supported by simulations for viscous flows. We suggest that this counterintuitive effect has potential implications for the air-transport of water droplets and the lifting of sediments in water.