Small-scale dynamics of settling, bidisperse particles in turbulence

Mixing and collisions of inertial particles at the small scales of turbulence can be investigated by considering how pairs of particles move relative to each other. In real problems the two particles will have different sizes, i.e. they are bidisperse, and the effect of gravity on their motion is often important. However, how turbulence and gravity compete to control the motion of bidisperse inertial particles is poorly understood. Motivated by this, we use direct numerical simulations (DNS) to investigate the dynamics of settling, bidisperse particles in isotropic turbulence. In agreement with previous studies, we find that without gravity (i.e. , where is the Froude number), bidispersity leads to an enhancement of the relative velocities, and a suppression of their spatial clustering. For , even though the typically defined Froude number is . This could imply, for example, that extreme events in the mixing of settling, bidisperse particles are only weakly affected by gravity even when . We also find that gravity drastically reduces the clustering of bidisperse particles. These results are strikingly different to the monodisperse case, for which recent results have shown that when

Duke Scholars

Author Andrew Bragg Civil and Environmental Engineering