Clustering characteristics of sub-Kolmogorov size droplets subjected to moderately turbulent co-flows

Interaction of sub-Kolmogorov size droplets with turbulent co-flows is investigated using Interferometric Laser Imaging for Droplet Sizing and Mie scattering techniques along with hotwire anemometry. A swirl atomizer was positioned at the center of a 48 mm diameter nozzle, which provided a turbulent co-flow. The turbulent flow characteristics were varied using perforated plate(s). For test conditions that the co-flow was provided, the mean bulk flow velocity was about 7 m/s. The results show that increasing the background root-mean-square (RMS) velocity fluctuations from 0 to about 1.5 m/s increases the most probable droplet diameter, cluster, and void sizes from about 33 to 43 μm, 660 to 770 μm, and 3.3 to 4.1 mm, respectively. The most probable cluster and void sizes are close to the Taylor and integral length scales, respectively. It was investigated that increasing the RMS velocity fluctuations increases uniformity in the spatial distribution of the droplets. It is inferred that, although increasing the RMS velocity fluctuations increases the most probable droplets size (which may not be desirable for many engineering applications), the enhanced uniformity in the distribution of the droplets is desirable.