Article ID: 18-00023
Dynamic behavior of binary water droplets approaching each other in cloud is simulated by the improved two-phase lattice Boltzmann method with the Continuum Surface Force (CSF) model. This method does not need to solve the pressure Poisson equation and enables us to calculate two-phase flows with high density ratio accurately and efficiently. In this study, we investigate the effects of the Reynolds number Re, the Weber number We, the impact parameter B (the relative distance between the centers of two droplets), and the droplet size ratio on the behavior of the binary droplets for liquid-gas density ratio of 800. We first simulate a stationary liquid droplet in a gas to confirm the validity of the present method. We next simulate off-center approach of two equal-size droplets and investigate the effects of the Reynolds number and the Weber number. It is seen that at low Weber numbers of We ~ O(10-2), there are two types of behavior during approach of two equal-size droplets, namely coalescence and deviation. In this Weber number region, it is found that they can deviate from each other at low Reynolds numbers of Re ≲ O(1) in spite of B ≤ 1.0, whereas collision and subsequent coalescence occur at higher Reynolds numbers of Re ≳ O(10). We finally simulate approach of two unequalsize droplets with various size ratios. It is found that the behavior of the droplets is different from that in the case of the equal-size droplets owing to asymmetric velocity field and droplet deformation. In addition, the smaller droplet tends to deviate from its original path more significantly than the larger droplet.
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series C
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A