Viscoelastic levitation

TL;DR

This paper demonstrates a novel viscoelastic levitation phenomenon where a rotating dense sphere near a wall levitates due to asymmetric elastic stresses, combining experiments, models, and simulations.

Contribution

It introduces a new levitation effect caused by viscoelasticity and shear asymmetry, supported by experimental, theoretical, and numerical analysis.

Findings

Sphere levitates at a fixed distance from the wall.

Levitation is governed by a universal elastic-to-gravitational force ratio.

The phenomenon occurs at small Deborah numbers.

Abstract

The effects of viscoelasticity have been shown to manifest themselves via symmetry breaking. In this investigation, we show a novel phenomenon that arises from this idea. We observe that when a dense sphere is rotated near a wall (the rotation being aligned with the wall-normal direction and gravity), it levitates to a fixed distance away from the wall. Since the shear is larger in the gap (between the sphere and the wall) than in the open side of the sphere, the shear-induced elastic stresses are thus asymmetric, resulting in a net elastic vertical force that balances the weight of the sphere. We conduct experiments, theoretic models, and numerical simulations for rotating spheres of various sizes and densities in a Boger-type fluid. In the small Deborah number range, the results are collapsed into a universal trend by considering a dimensionless group of the ratio of elastic to gravitational forces.