Elastic Convection in Vibrated Viscoplastic Fluids

TL;DR

This paper reports the discovery of boundary-free convection rolls in vibrated shear-thinning yield stress fluids, driven by vertical oscillation and governed by a non-dimensional stress parameter.

Contribution

It introduces a novel boundary-free convection phenomenon in viscoplastic fluids and identifies the governing non-dimensional stress controlling the transition.

Findings

Convection rolls form without container boundaries.

The transition occurs at a critical non-dimensional stress.

The convection is independent of hysteresis effects.

Abstract

We observe a new type of behavior in a shear thinning yield stress fluid: freestanding convection rolls driven by vertical oscillation. The convection occurs without the constraint of container boundaries yet the diameter of the rolls is spontaneously selected for a wide range of parameters. The transition to the convecting state occurs without hysteresis when the amplitude of the plate acceleration exceeds a critical value. We find that a non-dimensional stress, the stress due to the inertia of the fluid normalized by the yield stress, governs the onset of the convective motion.