The Effect of Swirling Air-to-Liquid Momentum Ratio on the Spray and Droplet Characteristics

The effect of swirl flow on the spray characteristics (structure, droplet diameter and droplet velocity) is experimentally investigated for varying air-to-liquid momentum ratios in this work. The diagnostic techniques employed include high-speed shadowgraphy and 1D-PDPA. A commercial pressure swirl injector is mounted in a swirl stabilized model gas turbine burner to investigate the spray characteristics with and without the presence of swirling flowfield under isothermal conditions. In the absence of the injector flow the burner produced a converging-diverging flowfield at the burner exit, influenced by the bluffbody effect near to the exit and the swirling intensity farther downstream. The investigations reveal an unmistakable influence of the swirling flow on the droplet size, velocity and spatial distribution. Under the investigated momentum flux ratios the conical spray structure is altered and the droplets size and velocity at each location changed with the spatial variation in the magnitude and nature of the swirling flowfield. In general fine droplets are produced near to the high velocity air inflow, and coarser droplets in the recirculation zone owing to the longer residence time. The mean axial velocity of the droplet reduced in presence of swirling flow, with the droplets showing negative velocities at downstream locations.