3d Numerical Simulation of Drop Coalescence∗

The major importance of drop coalescence in a number of natural and industrial processes provides the motivation for fundamental experimental and theoretical studies on its mechanics. One of the main difficulties of such investigations is related with the presence of a thin liquid film, typically of order 10−4 of the drop size. In numerical studies of coalescence this requires very fine spatial discretization which, combined with the numerical instabilities typical for multiphase flows may lead to enormous CPU time. In the present study, a boundary integral method for numerical simulation of 3D drop-to-drop interactions is considered in the case of Newtonian liquids and negligible inertial forces. The main attention is directed to the application of a multiple time step approach, which can reduce the computational time required with some orders of magnitude without influencing the accuracy of the solution. However, even with this improvement, the computational process is still far from useful in a more intensive investigation, especially for small capillary numbers, which is practically the most interesting case. A modification of the existing numerical methods for 2D film drainage and rupture, taken into account a 3D-based interaction force, proves to be a successful alternative to the simulations of 3D drop coalescence.