DNS of buoyancy-driven flows and Lagrangian particle tracking in a square cavity at high Rayleigh numbers

In this work we investigate numerically particle deposition in the buoyancy driven flow of the differentially heated cavity (DHC). We consider two values of the Rayleigh number (Ra = 10⁹, 10¹⁰) and three values of the particle diameter (d_p = 15, 25, 35 [μm]). We consider the cavity filled with air and particles with the same density of water ρ_w = 1000 [kg/m³] (aerosol). We use direct numerical simulations (DNS) for the continuous phase, and we solve transient Navier–Stokes and energy transport equations written in an Eulerian framework, under the Boussinesq approximation, for the viscous incompressible Newtonian fluid with constant Prandtl number (Pr = 0.71). First- and second-order statistics are presented for the continuous phase as well as important quantities like turbulent kinetic energy (TKE) and temperature variance with the associated production and dissipation fields. The TKE production shows different behaviour at the two Rayleigh numbers.The Lagrangian approach has been chosen for the dispersed phase description. The forces taken into account are drag, gravity, buoyancy, lift and thermophoresis. A first incursion in the sedimentation mechanisms is presented. Current results indicate that the largest contribution to particle deposition is caused by gravitational settling, but a strong recirculating zone, which liftoffs and segregates particles, contributes to decrease settling. Deposition takes place mostly at the bottom wall. The influence of lift and thermophoretic forces on particle removal is discussed in detail. Indeed, it is shown that the lift is responsible of particle deposition on the vertical cold surface.