ANALYSIS OF HOLLOW-CONE SPRAY INJECTED IN AN UNCONFINED, ISOTHERMAL, COANNULAR SWIRLING JET ENVIRONMENT

The present work experimentally investigates the near- and far-field breakup, dispersion, and coalescence characteristics of a hollow-cone spray in an unconfined, low speed coannular isothermal swirling air jet environment. All the experiments were conducted at fixed liquid flow rate (Re-N = 7900), with various levels of coflowing annular swirling air (Re-s = 1600, 3200, 4800, and 5600). Swirling motion was imparted to the coaxial air flow using a guided vane swirler with a blade angle of Phi = 45 degrees (corresponding geometric swirl number S-G = 0.8). Initial experiments were focused towards characterizing swirling air flow using PIV. Later the shadowgraphy technique was employed to study the effect of swirling air flow on the global and local dynamics of the spray. Measurements were made in the spray in both axial and radial directions. The data indicate that Sauter mean diameter (SMD) in the radial direction is highly reliant on the intensity of swirling air imparted to the spray. The spray is subdivided into two zones as function of swirling air in the axial and radial directions: (1) near field of the nozzle (ligament regime) where variation in SMD arises predominantly due to primary breakup of liquid films; (2) far field of the nozzle where dispersion and collision induced coalescence of droplets is dominant. Each regime has been analyzed meticulously, by computing the probability of primary breakup, the probability of coalescence, and spatiotemporal distribution of droplets which gives a probabilistic estimate of the aforementioned governing phenomena. In addition to this, spray global length scale parameters such as spray cone angle, breakup length, and wavelength of liquid film has been characterized by varying Re-s while maintaining constant Re-N.