Droplet distributions at the liquid core of a turbulent spray

Abstract

Initial droplet distributions at the liquid core are examined for various Weber number and pulsing conditions. While experimental investigation in the liquid core region is nearly impossible due to difficulty in the optical access to the region, the distribution at the region is investigated computationally, and typical droplet distributions are identified. It is found that the Nukiyama–Tanasawa and log-normal distributions can best describe the droplet size and velocity distributions, respectively. By comparing computational results obtained at the liquid core (0<x<8mm) and experimental data collected at x=48mm, it is suspected that the droplet gradation occurs immediately after droplets are separated from the liquid core. Thus, the distribution shape changes rapidly in both axial and radial directions. Such droplet–gradation behavior is numerically confirmed when the Nukiyama–Tanasawa droplet size distribution is used as an initial condition for the stochastic separated flow model. When the jet velocity is increased, the width of the droplet-size distribution becomes narrower, while the droplet velocity distribution becomes broader. Possible physical mechanism for that behavior is discussed in detail. Pulsing injection prominently influences the external spray shape near the nozzle exit. However, the overall droplet size and velocity distributions of the liquid core due to the pulsing injection are relatively insignificant for a turbulent spray in the atomization regime.