2 - Particle dispersion and preferential concentration in particle-laden turbulence

Abstract

Turbulence has important effects on both the average and instantaneous particle concentration fields. Dispersion describes the mean square displacement of particle trajectories from an average path, analogous to turbulent diffusion of flow tracers. This chapter reviews statistical theories for particle dispersion demonstrating the significance of particle inertia. Preferential concentration describes the effect of coherent structures, or eddies, on the instantaneous spatial distribution of inertial particles. For Stokes numbers near 1, turbulence structures produce dense clusters and large voids in the particle concentration field. Experimental and computational evidence of preferential concentration, physical explanations of the phenomena, and methods for quantifying clustering are discussed. Lastly, the chapter examines turbophoresis in wall-bounded turbulence where steep gradients in carrier phase turbulent kinetic energy produce very high mean particle concentrations near the wall. Particle–particle collisions within the high-concentration layer limit the peak mean concentration well below levels predicted by one- or two-way coupled simulations.