but obtained better agreement at higher pressures. Putorti measured drop size and velocity simultaneously using a two-color fluorescence technique in an axisymmetric sprinkler configuration. Putorti’s measurements provide drop size/velocity correlations, drop size distributions, and drop trajectories. Sheppard measured velocities very close to the sprinkler ( 0.2m) to characterize the initial spray velocity using Particle Image Velocimetry (PIV). This
technique allows for visualization of a cross-section of the spray. He presented these measurements in a spherical coordinate system having the origin located on the sprinkler centerline at a specified position between the orifice and the deflector plate. Sheppard showed the variation of radial velocity with polar angle (measured from the sprinkler centerline) at various azimuthal angles (measured from the sprinkler yoke arms). He compared his velocity measurements with PDI measurements noting discrepancies due to differences in experimental configu- ration and biasing issues related to the differing mea- surement approaches used in the respective diagnostic techniques.
Predicting spray characteristics has proven to be challenging because of the complexity and stochastic behavior of the breakup process. In fact, it is common to simply characterize the sprinkler spray using correlations, or curve fits, of available experimental data. These experimental data are often obtained at conditions well outside of the operating conditions of interest. However, Dombrowski and Johns [11] developed an actual atomiza- tion model based on wave dispersion theory to predict drop size. This atomization model was developed using fan type injectors. Dombrowski described the atomization process in terms of the growth of waves on an infinite unstable sheet. He simplified the wave dispersion equations and integrated them to quantify the sheet breakup character- istics and then related the sheet disintegration to initial drop characteristics. This wave dispersion model has been successfully used by Rizk for various types of fuel injection systems [12] and is applied to sprinklers in the current study. Marshall and di Marzo [13] have developed a complete atomization model for sprinklers by integrating a film formation sub-model proposed by Watson [14] with a sheet disintegration sub-model proposed by Dombrowski and Johns [11]. Furthermore, these models have been implemented with a modified stochastic formulation originally proposed by Rizk and Mongia [12]. The current study provides the details for this atomization modeling approach. Results from this atomization model are presented and comparisons are made with actual sprinkler measurements and correlations.