Fingerprints of Turbulence in the Deposition Patterns of Charged Particles

Particle deposition in wall-bounded flows, driven by the surrounding turbulence via the turbophoresis process, is augmented when particles are charged. This augmentation occurs in many familiar applications, including dust/ash ingestion in aircraft engines where particles are charged triboelectrically and electrostatic precipitation for filtration technologies where particles are charged from an external ionization source. However, the coupling between turbulence and electrostatic effects in the deposition problem and the conditions under which each effect dominates are still poorly understood. To explore this coupling, experiments were conducted in a vertical turbulence channel equipped with a high voltage ionization wire to prescribe electrostatic charges to the particles. Both the deposition on the wall and the velocity statistics of entrained particles approaching the wall were captured with high-speed cameras. Deposited particles were observed to form patterns with similar streaking features as particles in the viscous layer, which are known to preferentially concentrate in low momentum streaks. Furthermore, the global deposition rate is found to be strongly dependent on the velocity statistics of the entrained particles, which in turn show a strong sensitivity to the particle charge.