The settling velocity of heavy particles in an aqueous near-isotropic turbulence

The ensemble-average settling velocity, Vs, of heavy tungsten and glass particles with different mean diameters in an aqueous near-isotropic turbulence that was generated by a pair of vertically oscillated grids in a water tank was measured using both particle tracking and particle image velocimetries. Emphasis is placed on the effect of the Stokes number, St, a time ratio of particle response to the Kolmogorov scale of turbulence, to the particle settling rate defined as (Vs−Vt)/Vt where Vt is the particle terminal velocity in still fluid. It is found that even when the particle Reynolds number Rep is as large as 25 at which Vt/vk≈10 where vk is the Kolmogorov velocity scale of turbulence, the mean settling rate is positive and reaches its maximum of about 7% when St is approaching to unity, indicating a good trend of DNS results by Wang and Maxey (1993) and Yang and Lei (1998). This phenomenon becomes more and more pronounced as values of Vt/vk decrease, for which DNS results reveal that the settling ra...