Multi-scale interactions in turbulent mixed convection drive efficient transport of Lagrangian particles

Convection driven by an unstable temperature gradient can provide a means for significant vertical transport of dust grains and other aerosols. Moreover, in the presence of a mean shear, large scale streamwise-aligned roll structures appear. These rolls are a hallmark of what is known as mixed convection, and are known to efficiently transport heat and momentum vertically. However, it is not currently known how effective these rolls are for the vertical transport of inertial Lagrangian particles. To explore this, we highlight results from a series of coupled Eulerian-Lagrangian direct numerical simulations of mixed convection flows. By comparing pure free convection, no convection (channel flow), and mixed convection, we highlight how coherent rollers appearing at a moderate Richardson number lead to significant vertical transport of settling inertial particles emitted near the lower surface. We find that inertial particles tend to cluster in regions associated with large vertical heat fluxes, and the result is a larger overall concentration in the interior of the domain when compared to free convection, or a pure turbulent boundary layers.