External flow characteristics for effective droplet deformation and breakup in turbulence*

We investigate the deformation and breakup of an initial spherical droplet that disperses in the turbulent carrier flow using direct numerical simulations. Our previous work [1] has analyzed the occurrence of drop breakup, the breakup time, and the number and sizes of the child droplets as a function of the viscosity ratio and Weber number. In contrast, the characteristics of the external surrounding flow that effectively deforms and breaks up the droplet are still unclear. Close to the break-up threshold, low-viscosity droplets break into two child droplets of similar sizes, while high-viscosity forms a thin filament that leads to many tiny droplets. We aim to quantify the instantaneous external flow type surrounding the droplet for various viscosity ratios, based on the relative strength of vorticity and shear stresses. Finally, the correlation between the external flow type and the time development of the shape will permit the identification of the mechanism for effectively deforming and breaking the droplet.

[1] Farsoiya, Palas Kumar, Zehua Liu, Andreas Daiss, Rodney O. Fox, and Luc Deike. "Role of viscosity in turbulent drop break-up." Journal of Fluid Mechanics 972 (2023): A11.