Settling of heated particles in homogeneous turbulence

We consider the case of inertial particles heated by thermal radiation while settling by gravity through a turbulent transparent gas. Numerical simulations of forced homogeneous turbulence are performed taking into account the two-way coupling of both momentum and temperature between the dispersed and continuous phases. Particles much smaller than the smallest flow scales are considered and the point-particle approximation is adopted. The particle Stokes number (based on the Kolmogorov time scale) is of order unity, while the nominal settling velocity is up to an order of magnitude larger than the Kolmogorov velocity, marking a critical difference with previous two-way coupled simulations. It is found that non-heated particles enhance turbulence when their settling velocity is sufficiently high. When heated, particles shed plumes of buoyant gas, further modifying the turbulence structure. At the considered radiation intensities, clustering is strong but the classic mechanism of preferential concentration is modified, while preferential sweeping is eliminated or even reversed. Particle heating also causes a significant reduction of the mean settling velocity, which is caused by positively buoyant plumes in the vicinity of particle clusters. The downward drag force exerted by the particles on the fluid breaks the symmetry of the un-laden turbulence and increases the magnitude of the vertical velocity fluctuations in the unheated case. This asymmetry is reduced in the presence of radiative heating due the reduced falling speed of the heavier particles, where buoyancy effects counteract gravity and the preferential sweeping mechanism.