Numerical investigation of the near head-on collision dynamics of non-newtonian droplets: a comparative study using the volume of fluid and the local front reconstruction method

Droplet-droplet interactions of highly viscous liquid suspensions have a major impact on industrial processes such as spray drying, fuel combustion, or waste treatment. The efficiency of these processes depends heavily on the morphology of the droplets after the collision (i.e., surface area and volume). Although often encountered, the physical mechanisms governing merging and break-up of non-Newtonian droplets are largely unknown. It is therefore of paramount importance to gain a better understanding of the complex physics dominating the collision of non-Newtonian droplets. In this research, we investigate numerically the collision of droplets using the local front reconstruction method (LFRM) and the volume of fluid (VOF) method. The coalescence and stretching separation regime are studied using a xanthan solution, whose shear-thinning rheology is described with the Carreau−Yasuda model. The capabilities of the two methods to capture the complex topological changes are assessed by a one-to-one comparison of the numerical results with experiments for near head-on collisions at various We numbers.