Experimental investigation of shock-induced tandem droplet breakup

For deeper insights into the dynamics of dense sprays, the present experimental work investigates the shock-induced breakup of two identically sized water droplets in tandem formation. The breakup process is visualized in a shadowgraph system and captured by an ultra-high-speed camera. The experimental Weber number ranges from 13 to 180, and the separation distance between the droplets is varied between 1.2 and 10.5 times of the droplet diameter. While the tandem formation exerts marginal influence on the lead droplet, the breakup intensity of the trailing droplet is consistently attenuated as the separation distance falls below critical levels. The time of initial deformation is postponed, the maximum cross-stream diameter is reduced, and the mean drag coefficient is lowered. These effects are more profound at lower Weber numbers and closer separation distances. The attenuation of the breakup intensity is also reflected by the formation of smaller bags in bag and bag-and-stamen morphologies and by the narrower cross-stream dispersion of fragments in multibag and shear stripping morphologies. When positioned in close proximity to the lead droplet, the trailing droplet fails to follow the conventional breakup morphologies. Instead, it either punctures or coalesces with the lead droplet.