Vertical dispersion of light inertial particles in stably stratified turbulence: The influence of the Basset force

The dispersion of light inertial particles [rho(p)/rho(f)=O(1)] in statistically stationary stably stratified turbulence is studied by means of direct numerical simulations. The light particle dispersion behavior is found to be comparable to that of heavy particles when displayed as a function of the Stokes number. Deviations from fluid particle dispersion are found already for small Stokes numbers; the length of the typical plateau for vertical dispersion is shorter for the light inertial particles. All the forces in the Maxey-Riley equation are taken into account and they are found to be of similar magnitude as the Stokes drag for particles with rho(p)/rho(f)=O(1). However, not all forces directly influence the particle dispersion. It is shown that especially the often neglected Basset force plays a considerable role in the vertical dispersion of light particles in stratified turbulence. Neglecting this force results in an overprediction of the vertical dispersion by about 15%-20%.