Abstract
The present experimental study investigates the shear stripping breakup of single droplets in subsonic and supersonic gaseous flows. In contrast to most research that places emphasis on the Weber number (We), we focus on the individual effects exerted by flow Mach (M∞) and Reynolds numbers (Re). Millimeter-sized droplets made of either ethylene glycol or water are exposed to shock-induced flows. Shadowgraph and schlieren images of the breakup process are recorded by an ultra-high-speed camera. The experimental We is constrained at 1100, while M∞ is varied from 0.3 to 1.19 and Re from 2600 to 24,000. A systematic analysis of the experiment series reveals that the breakup pattern alters with M∞ although a constant We is maintained. The classical stripping behavior with fine mist shed from the peripheral sheet changes to rupture of multiple bags along the periphery at M∞ = 0.63, and further to stretching of ligament structures from the leeward surface at M∞ = 1.19. The corresponding breakup initiation is delayed and the resultant fragments are sized less uniformly and distributed over a narrower spread. In terms of the early-stage deformation, droplets experience less intense flattening and slower sheet growth at higher M∞. The change of Re introduces additional variations, but only to a minor extent.Graphical abstract
Highlights
Droplet breakup, termed secondary atomization, refers to the fragmentation of a droplet subjected to aerodynamic forces
The Weber number represents the ratio between the disruptive aerodynamic force and the restorative surface tension, and the Ohnesorge number compares the viscous force to the surface tension
Page 3 of 17 193 the current work, we focus on the stripping breakup and adopt the concept proposed by Theofanous and Li (2008)
Summary
Termed secondary atomization, refers to the fragmentation of a droplet subjected to aerodynamic forces. This phenomenon is relevant in diverse applications, such as fuel injection (Reitz and Diwakar 1986), spray coatings (Mostaghimi et al 2002) and metal powder production (Lagutkin et al 2004). Where ρg and ug are the density and the velocity of the gas flow, and d0, σ, μd and ρd are the initial diameter, the surface tension, the dynamic viscosity and the density of the liquid droplet, respectively. The Weber number represents the ratio between the disruptive aerodynamic force and the restorative surface tension, and the Ohnesorge number compares the viscous force to the surface tension.
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