The breakup process of a liquid jet injected into crossflow was experimentally studied, the primary objective was to identify intermittent coherent structures associated to the four specific spray regimes: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The approach introduces a novel modal extraction technique utilizing Multi-Resolution Dynamic Mode Decomposition (MrDMD) developed by Kutz et al. [1]. The applied methodology identifies the liquid surface's coherent structures and is an extension of currently used Dynamic Mode Decomposition (DMD). The key benefit of MrDMD is it parses nonlinear dynamical systems into multiresolution time-scaled components to capture intermittent mechanisms. MrDMD is applied to time-resolved series of column region snapshots for the four spray regimes. Relative frequencies of each breakup regime are extracted and identified. The frequencies for the characterized fuel jet injection dynamics are linked to critical nondimensional parameters known as the Strouhal number. Results show that ligament shedding is a dominant breakup structure that is prevalent within the enhanced capillary breakup regime and associated with a Strouhal number of St = 0.055 ± 0.006 it is found this breakup structure within all breakup regimes. Bag breakup predominant in the bag breakup regime and the multimode regime is associated with the nondimensional oscillating frequency of St = 0.14 ± 0.004. Shear breakup associated with the breakup of small-scale structure from the liquid jet is found to be correlated to the shedding St = 0.23 ± 0.008. It is found that shear breakup is the dominant mode of breakup in the shear breakup regime and it is also a contributing mechanism downstream of the multimodal breakup.
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