Numerical simulation of binary liquid droplet collision

Abstract

A numerical investigation of binary droplet collision has been conducted. The complete process of the collision of two liquid droplets is dynamically simulated by solving the incompressible Navier-Stokes equations coupled with the convective equation of the level set function that captures the interface between the liquid and the gas phases. The simulations cover four major regimes of binary collision: bouncing, coalescence, reflexive separation, and stretching separation. For water droplets in air, the numerical results are compared with the experiments by and Ashgriz and Poo [J. Fluid Mech. 221, 183 (1990)] on collision consequences. For hydrocarbon (C14H30) droplets in nitrogen gas, the simulated results are compared in detail with the time-resolved photographic images of the collision processes obtained by Qian and Law [J. Fluid Mech. 331, 59 (1997)] in every collision regime. The present numerical results suggest that the mechanism of a bouncing collision is governed by the macroscopic dynamics. However, the fact that the present macroscopic numerical model is unable to capture the collision regime of coalescence after minor deformation supports the speculation that its mechanism is related to the microscopic dynamics. Furthermore, the transition from bouncing to coalescence collisions has been predicted and agrees well with the analytical model. The mechanism of satellite droplet formation for head-on collision and stretching separation collision is also studied based on the detailed time-resolved dynamic simulation results. It is then confirmed that end pinching is the main cause of satellite formation in head-on collisions whereas the capillary-wave instability becomes dominant in large impact parameter cases. In the case of an intermediate impact parameter, the effects of twisting and stretching due to the angular momentum and the inertia of the colliding droplets are significant for the satellite formation.

3D Coalescence Collision of Liquid Drops Using Smoothed Particle Hydrodynamics

“…Another possible scenario when two drops collide in a vacuum environment is the fragmentation of the drops. Many studies has been proposed for the numerical simulation of the coalescence and break up of droplets (Azizi & Al Taweel, 2010;Cristini et al, 2001;Decent et al, 2006;Eggers et al, 1999;Foote ,1974;Jia et al, 2006;Mashayek et al, 2003;Narsimhan, 2004;Nobari et al, 1996;Pan & Suga, 2005;Roisman, 2004;Roisman et al, 2009;Sun et al, 2009;Xing et al, 2007;Yoon et al, 2007). In these studies, the authors propose different methods to approach the dynamics of liquid drops by a numerical integration of the Navier-Stokes equations.…”

Multiphase Flow

“…Pan and Suga [171], for example, performed 3D dynamic simulations of binary droplets collisions for cases of different Weber numbers and impact parameters. The systems used are water drops in air and tetradecane drops in nitrogen at atmospheric conditions.…”

Coalescence collision of liquid drops I: Off-center collisions of equal-size drops

“…The simulations cover four regimes of binary collisions: bouncing, coalescence, reflexive separation and stretching separation. The numerical results reported in 30 suggest that the collisions that lead to bouncing between the drops are governed by the macroscopic dynamics. The authors also studied the mechanism of formation of satellite drops, confirming that it is the "end pinching" the principal cause of the formation of satellite drops, while the capillary wave instabilities are the dominant feature in cases where a large value of parameter impact is employed.…”