LIQUID-FILM BREAK-UP IN A MODEL OF A PREFILMING AIRBLAST NOZZLE

The paper describes the atomisation process of a liquid in an axissymm etric shear layer formed through the interaction of turbulent coaxial jets (respectively, inner and outer jets), with and without swirl, in a model airblast prefilming atomiser. The atomisation process and spra y quality was studied using different visualisation techniques, namely laser shadowgraphy and digital image acquisition. The experiments wer e conducted for different liquid flow rates, Reynolds numbers ranging from 6600 to 66000 and 27300 to 92900 for the inner and outer air flow s, respectively, for different outer flow swirl levels, and two liquid film thicknesses -0.2 and 0.7 mm. All the tests were carried out at a tmospheric pressure and using water. The results include the analysis of the film structure at break-up and of the break-up length, and sugg est that the deterioration of the liquid film close to the atomising e dge exhibits a periodic behaviour and is mainly dependent on the inner air velocity. Film thickness strongly affects the time and length sca les of the break-up process for the lower range of air velocities. For higher inner air velocities, the break-up length and time become less dependent on liquid flow rate and initial film thickness.