  We recently found wall-bounded turbulence to suppress and control bipolar
triboelectric charging of particles of identical material. This control is due
to fluid modifying the motion of light particles. Thus, the particles' charge
distribution depends on their Stokes number distribution. More specifically,
fluid forces narrow the bandwidth of the charge distribution, and bipolar
charging reduces dramatically. Consequently, not the smallest but mid-sized
particles collect the most negative charge. However, the influence of the
Reynolds number or particle concentration on bipolar charging of polydisperse
particles is unknown. This paper presents the charging simulations of
same-material particles the in different wall-bounded flows. In a comprehensive
study, we vary the Reynolds number from $Re_\tau=$ $150$ to $210$ and the
particle number density from $4 \times 10^9 \ \mathrm{m}^{-3}$ to $1 \times
10^{10} \ \mathrm{m}^{-3}$ to further explore the influence of the carrier flow
on bipolar charging. We model charge transfer based on the balance of
transferable charge species. Such species can represent adsorbed ions
transferred during collisions or free electrons captured into a lower energy
state on the other surface. The turbulent flow is modeled via Direct Numerical
Simulations (DNS) and is coupled to the particulate phase modeled via the
Discrete Element Method (DEM). Overall, our multiphysics approach couples the
fluid dynamics, electric field, triboelectric charging, and particle momentum
into one complex simulation.
