Study of droplet collision regimes using the lattice-Boltzmann method

A multiphase pseudopotential lattice-Boltzmann (PP-LB) based model was implemented to investigate the effect of the impact factor (B) on binary collisions of water droplets. The thermodynamic consistency of the PP-LB model was assessed, showing good agreement with the analytical vapor-liquid equilibrium (VLE) coexistence curve given by the Peng-Robinson equation of state, yielding an average error for the equilibrium densities below 4%. The time evolution of an ellipsoidal oscillating droplet was accurately predicted, with deviations of the oscillation period with respect to the analytical solution below 1%, serving as a benchmark to validate the PP-LB in transient conditions. Lastly, binary droplet collision simulations were conducted using the properties of a water-air system, identifying different regimes (both head-on and off-center coalescence, reflexive separation, and stretching separation) and investigating their characteristic features such as liquid filament formation, droplet rotation, satellite droplet formation. The effect of the impact factor was examined, finding that as B increases, the formation of satellite droplets is favored. In addition, a droplet rotation was observed, due to the inertia and vertical distance between the centers of the droplets.