Experimental investigation of secondary atomization in high-speed gas flow

This study develops empirical correlations for the secondary atomization dynamics of water droplets exposed to high-speed flows spanning three orders of Weber number magnitude ( We ∼ O(10¹)–O(10³)). It achieves this by employing shock-tube experiments coupled with time-resolved shadowgraph imaging. Over 100 trials resolve the deformation and breakup processes across subsonic to supersonic regimes. Thereby, the cross-stream deformation rates, maximum flattening ratios, and dimensionless breakup initiation times ( τ _b,i) were quantified as functions of We . The results reveal that a two-stage trend in τ _b,i emerges: a rapid decay below We ∼ 500 transitions to a gradual saturation above We ∼ 1500. This is consistent with a shift in breakup regime dominance from bag-type breakup to shear-induced entrainment. A novel grayscale intensity analysis method isolates the core droplet morphology from the surrounding satellite mist. This enables a precise tracking of the transient mass shedding. Core flattening persists until perimeter shear stripping initiates an exponential mass decay that follows a We -independent scaling law in the shear/ Catastrophic regime. Spatial satellite distributions (resolved via high-resolution digital in-line holography (DIH)) reveal We -dependent shedding mechanisms governed by the transition from bag-type ( We ∼ O(10¹))to transition from bag-type to shear-driven ( We ∼ O(10²)) and shear-driven breakup ( We ∼ O(10³)). The transient drag coefficient for the core droplet depends on its aspect ratio, which evolves dynamically with shape deformation and mass shedding. Integrating these correlations for secondary atomization and time-varying drag yields trajectory predictions for core droplet that exhibit deviations less than 7% from experimental data across the tested conditions. This demonstrates the enhanced predictive accuracy of the proposed models over a broad We range.