The effect of Electrostatic Forcing on the Droplet Distributions in Swirling Coaxial Atomization*

Multiphysics actuation is a promising strategy for versatile control of atomization. We present results of an experimental study where electrostatic forcing is applied at the nozzle of a swirling coaxial airblast atomizer, and along the mid-field spray development. Laser interferometry (PDPA) measurements of droplet sizes, as well as of axial and radial velocities, were collected across a representative cross section of the spray, over a wide range of gas to liquid momentum ratios, gas swirl ratios and electric field strengths. Electrostatic forcing resulted in smaller mean droplet diameters, especially for the lower momentum ratios studied. We observed significant increases in the axial and radial droplet velocities due to electrostatic acceleration, leading to more radially uniform sprays. These effects were detectable at all swirl ratios explored. Larger relative increases in the velocities of smaller droplets due to electrostatic effect contribute to the more uniform profiles of electrified sprays. Finally, we compare the observed droplet concentration and mean droplet diameter radial profiles with simple models that account for the electrostatic forcing of the spray, together with a simple scaling law for the electric charge density of each droplet.