  Current models predict particles of the same material but different sizes to
charge bipolar upon contacts; the resulting charge peaks endanger process
safety. However, we found wall-bounded turbulence to suppress the powder's
electrostatic charging. Aerodynamic forces skew the collision frequency and
narrow the charge distribution's bandwidth. Bipolar charging reduces,
especially in moderately polydisperse systems of a low Stokes number. Not the
smallest but mid-sized particles charge most negatively. Moreover, turbulence
separates charge, producing pockets of high electric potential in low-vorticity
regions.
