Inertia dominated drop collisions. I. On the universal flow in the lamella

This study is devoted to the analysis of inertia dominated axisymmetric drop collisions with a dry substrate or with another liquid drop. All the previous theoretical and semiempirical models of drop collisions are based on the assumption that the flow in the lamella and its thickness are determined by the impact conditions, mainly by the Reynolds and Weber numbers. In this study the existing experimental data are compared to existing and new numerical simulations for the shape of the lamella generated at the early times of drop impact for various impact conditions. The results show that if the Reynolds and Weber numbers are high enough, the evolution of the lamella thickness almost does not depend on the viscosity and surface tension. Therefore these results completely change our understanding of the flow generated by drop collisions. Moreover, we demonstrate that the theoretical models based on the approximation of the shape of the deforming drop by a disk and the models based on the energy balance approach are not correct. Finally, universal dimensionless distributions for the lamella thickness, velocity, and pressure are obtained from the numerical simulations of drop impact onto a symmetry plane (associated with the binary drop collisions). These universal distributions are valid for high impact Weber and Reynolds numbers.