Effects of roughness on particle dynamics in turbulent channel flows: a DNS analysis

Deposition and resuspension mechanisms in particle-laden turbulent flows aredominated by the coherent structures arising in the wall region. These turbulentstructures, which control the turbulent regeneration cycles, are affected by theroughness of the wall. The particle-laden turbulent flow in a channel boundedby irregular two-dimensional rough surfaces is analysed. The behaviour of dilutedispersions of heavy particles is analysed using direct numerical simulations (DNS)to calculate the three-dimensional turbulent flow and Lagrangian tracking to describethe turbophoretic effect associated with two-phase turbulent flows in a complex wallboundeddomain. Turbophoresis is investigated in a quantitative way as a function ofthe particle inertia. The analysis of the particle statistics, in term of mean particleconcentration and probability density function (p.d.f.) of wall-normal particle velocity,shows that the wall roughness produces a completely different scenario compared tothe classical smooth wall. The effect of the wall roughness on the particle mass flux isshown for six particle populations having different inertia.