The influence of imaging method on high-speed droplet breakup measurements

High-speed imaging methods are foundational to experimental studies of shock-droplet interactions. The bulk of experimental droplet breakup data has been obtained with shadowgraphy, which records an integrated cross section of all mass in the region of interest. Alternative imaging methods such as laser-induced fluorescence (LIF), which images photons emitted from dye excited by a laser, have only been used in a limited capacity. When imaging the same breakup event, the images produced by different techniques are distinct, and to date, no efforts have been made to critically evaluate to what extent the imaging method influences quantitative measures and model validation. In this paper, we compare experimental measurements obtained using shadowgraphy and LIF to quantitatively consider the effect these methods have on interpretation of droplet physics. Differences in observed droplet morphology are highlighted, and dependencies in deformation and displacement measurements are examined. Extant breakup models are evaluated against experimental data to establish the significance of imaging method on model validation. The relative merits of each technique are summarized and recommendations for future studies are made.