AERODYNAMIC CHARACTERISTICS OF SWIRLING SPRAY FLAMES - PRESSURE-JET ATOMIZER

The effect of swirl on droplet transport processes is examined in a pressure-atomized, hollow-cone kerosene spray, introduced into coflowing nonswirling and swirling air flow fields. An ensemble light scattering technique, based on measurement of the polarization ratio, provided spatially resolved measurements on the local values of droplet mean size and number density in dense regions of the nonburning spray. Laser velocimetry was employed to measure the axial, radial, and tangential velocity components of the droplets and combustion air stream. Droplet velocity distributions and time histories provided information on the transport of individual droplets under nonburning and burning conditions. High-speed cinematography, short-exposure photography, and video movies were also employed to observe the global features of the spray flame. The results reveal that the spray flame has a complex three-dimensional structure. The introduction of swirl to the combustion air modifies the droplet/air velocity field in addition to the spatial distribution of droplet size and number density. Larger droplets are transported downstream relatively unperturbed by the surrounding air stream while smaller droplets are entrained by the recirculating aerodynamic pattern. In addition, observed instabilities during liquid jet breakup appear to result in droplet clustering further downstream. The interaction between the fuel droplets and air flow field is therefore a process that significantly affects the overall characteristics of spray flames. Regulation of fuel/air interactions can mitigate fuel losses into the surrounding environment as well as control flame stability.