Effects of aerodynamic interactions on the motion of heavy particles in a bidisperse suspension

The effect of local aerodynamic interactions on the motion of heavy particles in a bidisperse suspension in both quiescent and turbulent air is studied by a hybrid simulation and a theoretical treatment. The particles are assumed to be small in size compared to the Kolmogorov length of the carrier air turbulence, and Stokes disturbance flows are used to represent the effect of particles. We first consider the case of no background air turbulence to validate the numerical and theoretical approaches by comparing with previous results in suspension mechanics. In a bidisperse suspension with background air turbulence, in addition to the previously known increase due to preferential sweeping, aerodynamic interactions contribute to a second augmentation in mean settling rate which depends on the flow dissipation rate. This additional increase in settling rate due to local aerodynamic interactions is also coupled with preferential concentration, in agreement with the experimental observations of Aliseda et al. (2002, Journal of Fluid Mechanics, 468, 77-105). In all cases, the numerical results are explained by the theoretical approach.