Dispersion of evaporating droplets in a swirling axisymmetric jet

The effects of swirl and vaporization on droplet dispersion are investigate d in the near region of a two-phase, swirling, heated jet. Simulations are based on the numerical solution of time-dependent, axisymmetric gas-phase e quations, Droplets' trajectories are tracked by using a Lagrangian approach . For all of the swirl cases investigated, the droplet dispersion exhibits a nonmonotonic behavior, with the maximum dispersion occurring near Stokes number (St) unity. As the swirl intensity is increased, the radial dispersi on of both nonevaporating and evaporating droplets is significantly enhance d. We attribute this dispersion enhancement to two factors: 1) increased vo rtex pairing interactions caused by swirl and 2) transfer of gas-phase swir l momentum to droplets, The effect of vaporization on dispersion is charact erized in terms of droplet lifetime compared to its response time and the c haracteristic how time. For the investigated conditions, the dispersion of evaporating droplets is noticeably reduced compared to that in the nonevapo rating case. The dispersion function vs St behavior is also modified due to vaporization, Droplets with diameters smaller than the optimum value are s ufficiently vaporized during their interaction with the vortex rings, and t heir dispersion approaches the low-St limit. On the other hand, droplets wi th diameters larger than the optimum are not vaporized significantly. Conse quently, their dispersion follows the large-St behavior.