Cyril Gadal

Influence of normal stress differences on the structure of dense granular flows

Normal stress differences are a non-Newtonian effect found in various materials, such as dense suspensions, viscoelastic polymers or granular media, often linked to their non-trivial microstructure. When these materials flow, normal stress differences modify the stress distribution within the material, leading to peculiar effects. In the case of dense granular flows down an inclined chute, we will show, using a combination of experiments, mathematical modelling and numerical simulations at the grain scale, that normal stress differences induce the curvature of the flow surface, but also a hidden secondary flow structure. The former will be used to infer a value for the second normal stress difference by combining mathematical modelling and experiments, while the latter will be used to explain the emergence of beautiful patterns in polydisperse coloured granular flows.