Successive impact of multiple droplets on liquid film

Multiple droplets impinging on a thin liquid film successively is numerically studied using a three dimensional model with implementing a random disturbance subjected to Gaussian distribution. This model is very effective to predict the droplet splashing under relatively high impinging momentum, which is validated and has a fairly good agreement with experimental observation, measurement and analytical mechanism. Results show that the successive impact of multiple droplets can increase the splashing thresholds for the trailing droplets due to radial flow inside residual film. Collision of the primary crown induced by leading droplet and the secondary crown induced by trailing droplet results in bubble entrainment and wall deformation of the primary one, which will be further aggravated by vortexes induced in the gas phase and breakup of the secondary crown. Besides, radial expansion of the primary crown is determined by the flow resistance and radial momentum, but its vertical expansion is dominated by the liquid mass entering into it, based on which the crown diameter and height are discussed in terms of Weber number, initial film thickness and droplets vertical spacing, respectively. Finally, the impact area and minimum residual film thickness are addressed, and it is found that the droplets vertical spacing has negative effects on them. This study provides preliminary understanding of multiple droplets impact without consideration of solid-film heat transfer. (C) 2018 Elsevier Masson SAS. All rights reserved.