Optical visualization and measurement of liquid jet core in a coaxial atomizer with annular swirling air

This paper reports application of the optical connectivity (OC) technique for visualization and measurement of primary liquid jet core in a coaxial air-blast atomizer with annular swirling air flow. Experiments were conducted for various injector operating flow conditions corresponding to Weber number (We g ) and air-to-liquid momentum flux ratio (M) in the range 80–300 and 1–8, respectively. The air swirl number, S, was varied in the range 0–0.8 using different air swirlers within the atomizer. The image processing methods for characterization of jet breakup length and jet instabilities were described in detail. Visualization of the instantaneous images of the jet core captured by the OC technique in the absence and presence of air swirl were presented. Both mean and fluctuations of liquid jet breakup lengths were calculated. An experimental correlation was obtained for mean breakup length, which was found to bear a nonlinear inverse relation with both M and S. The air swirl was found to increase the fluctuations of jet breakup length signifying higher unsteadiness in the jet breakup process. Preliminary results on characterization of jet instabilities based on identification of liquid–air interface location on either side of the injector axis on the OC images were presented. The differences due to the effect of air swirl on jet instabilities close to the injector exit and near the mean jet breakup point were discussed.