Two-way coupled numerical simulation of electrospray with induced gas flow

The gas flow induced by droplet motion has been included in the numerical simulation of electrosprays. Steady state solutions were sought iteratively in a computational scheme that fully couples a 3D Lagrangian model for the droplet dynamics with a steady state 2D axisymmetric Eulerian model for the induced gas flow. To resolve the reactive drag force on the gas by the droplets we employ Gaussian filters with variable kernel widths that depend on the droplet number density. We have applied this scheme to an experimentally characterized spray from the literature comprised of non-evaporating primary and satellite droplets in air. The predicted characteristics of the droplet plume (droplet number density, droplet velocity, droplet size distribution) better match the experimental values when the induced airflow is accounted for than when it is not (assuming still air). It is shown that the induced airflow contributes to faster moving droplets, shrinkage of plume, and a prominent flux about the spray axis (centerline), as compared with the simulations assuming still air. Induced airflow results in an increase of 80% in axial droplets velocity at the centerline at the collection counterplate. The ratio of mass flux at the centerline between the cases of moving and still air equals 2.6 at the counterplate. We have also observed that the radial segregation by size of the satellite droplets is sensitive to the functional relationship between their charge-to-mass ratio and diameter. Induced gas flow is expected to have important implications in the simulation of droplet evaporation and vapor concentration in electrosprays.