Natural emergence of the Brazil-nut effect in granular flow models without explicit segregation terms

Determine whether continuum models for dry granular flow that do not include explicit size-segregation mechanisms can, without tuning or added segregation terms, spontaneously generate the Brazil-nut effect in which larger particles rise to the surface.

Background

The bidisperse thin-film viscous-suspension model developed in the paper reproduces the Brazil-nut effect without embedding a dedicated segregation mechanism.

Motivated by this, the authors explicitly ask if an analogous natural emergence is possible in granular flow models where no explicit size-segregation physics (e.g., void filling or kinetic sieving) is prescribed.