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Separate and joint clustering characteristics of large Stokes number sprays subjected to moderately turbulent co-flows

Ali RostamiRi LiSina Kheirkhah
Dec 2022
Separate and joint droplets, clusters, and voids characteristics of spraysinjected in a turbulent co-flow are investigated experimentally. SimultaneousMie scattering and Interferometric Laser Imaging for Droplet Sizing along withseparate hotwire anemometry are performed. The turbulent co-flowcharacteristics are adjusted using zero, one, or two perforated plates. TheTaylor length scale-based Reynolds number varies from 10 to 38, and the Stokesnumber estimated based on the Kolmogorov time scale varies from 3 to 25. Theresults show that the mean length scale of the clusters normalized by theKolmogorov length scale varies linearly with the Stokes number. However, themean void length scale is on the order of the integral length scale. It isshown that the number density of the droplets inside the clusters is about 10times larger than that in the voids. The ratios of the droplets numberdensities in the clusters and voids to the total number density are independentof the test conditions and equal 8.3 and 0.7, respectively. The jointprobability density function of the droplets diameter and clusters area showsthat the droplets with the most probable diameter are found in the majority ofthe clusters. It is argued that intensifying the turbulence broadens the rangeof turbulent eddy size in the co-flow which allows for accommodating dropletswith a broad range of diameters in the clusters. The results are ofsignificance for engineering applications that aim to modify the clusteringcharacteristics of large Stokes number droplets sprayed into turbulentco-flows.