Viscous effect on the droplet deformation process under high Weber number conditions

To explore the effect of droplet viscosity on the deformation process, and have a deep understanding of the mechanism of the droplet deformation and breakup process.Droplet deformation behaviors of three viscous silicone oils were experimentally captured by the high-speed shadowgraphic technique on a horizontal shock tube, the Weber number (We) ranged between 1 100～4 400. Results show that with the increasing of droplet viscosity: new deformation characteristics appear, and the duration that the droplet evolves into the special shape increases; The growth rates of characteristic space and displacement parameters all decrease, while the duration of the deformation process, the maximum of the droplet deformation extent/displacement all increase. This is because the enlarged viscous force has slowed down the deformation rate, consumed more inertia, and extended the deformation process;The most unstable wave of Kelvin-Helmholtz instability develops toward a larger scale and a slower growth rate tendency, thus the delaying effect caused by the viscosity on the deformation process is achieved.With the increasing of the maximum of deformation displacement, the maximum of droplet deformation extent firstly shows a linear growth trend then a slower growth rate.