Inverse lift: a signature of the elasticity of complex fluids?

TL;DR

This paper investigates the elastic properties of complex fluids like foam by measuring their response to flow around an obstacle, revealing an inverse lift phenomenon linked to elasticity.

Contribution

It introduces a novel experimental setup to observe inverse lift in elastic complex fluids and explains this phenomenon through elasticity-related correlations.

Findings

Inverse lift observed in foam flow around an obstacle.

Elasticity explains the direction of the lift.

Potential generality of inverse lift in elastic complex fluids.

Abstract

To understand the mechanics of a complex fluid such as a foam we propose a model experiment (a bidimensional flow around an obstacle) for which an external sollicitation is applied, and a local response is measured, simultaneously. We observe that an asymmetric obstacle (cambered airfoil profile) experiences a downards lift, opposite to the lift usually known (in a different context) in aerodynamics. Correlations of velocity, deformations and pressure fields yield a clear explanation of this inverse lift, involving the elasticity of the foam. We argue that such an inverse lift is likely common to complex fluids with elasticity.