Clustering of charged particles in a vertical turbulence channel

Particles in many familiar multiphase flows, including desert sand in atmospheric flows, biomass particles in fluidized bed reactors, planetary dust in spacecraft landings, and ash in volcanic eruptions, naturally accumulate large electrostatic charges either triboelectrically or through exposure to an external ionization field. To investigate how particle charges modulate particle-turbulence interactions, experiments in a unique vertical turbulence channel equipped with modifications to study electrostatics were conducted. Of particular interest is how electrostatic interactions alter particle clustering and streaking dynamics in the turbulent boundary layer. To study this problem, two high-speed cameras were used to capture particle trajectories in the wall-normal and wall-parallel planes, which allows particle clustering dynamics to be directly correlated to particle-wall interactions. After individual trajectories are captured using a Lagrangian particle tracking algorithm, clusters are identified using a Voronoi tessellation analysis and tracked in time. By measuring variations in both pair-wise clustering statistics and the dynamics of the identified clusters, the critical range of the electrostatic Stokes number where electrostatic interactions are comparable to particle-turbulence interactions can be identified. These findings help unveil the role of electrostatic forces on particle clustering and deposition dynamics in turbulent boundary layers.