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The present paper investigates experimentally the splashing dynamics of two-component droplet wall film interactions. Over a wide range of Weber numbers and dimensionless film thickness, the different combinations of two low surface tension fluids, e.g. hexadecane and hyspin, including their corresponding one-component interactions, have been considered. As a first step, the splashing morphology is examined and the respective similarities with open literature data are reported. In addition, the splashing dynamics is investigated evaluating quantitatively the time evolution of crown height and diameter, the total number of liquid jets (fingers) generated at the upper crown rim as well as the total number of ejected secondary droplets including their corresponding diameter, cumulative volume and velocity magnitude. The results are analysed by various post-processing procedures aiming to provide a large dataset, which can be efficiently used for the validation of numerical models. Furthermore, the importance of the impact morphology for understanding the impact dynamics is pointed out.

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Single drop impacts on thin liquid layers are of particular interest because of the ejection of secondary droplets, the so-called splashing. Only a few studies handle the deposition/splashing limit for two-component interaction, where the liquid properties of the impacting drop and wall film differ significantly. This study aims at identifying a unified approach for one-and two-component interactions to determine the deposition/splashing limit. Therefore, a large database of both interactions is considered, which includes data from literature for one-component interactions plus the following binary combinations: hyspin-hexadecane, diesel-hexadecane and diesel-motor oil. Furthermore, a systematic study of two-component interactions with several silicon oils and hexadecane is performed. To map the outcomes, the Ohnesorge number Oh and the Reynolds number Re calculated with arithmetically averaged fluid properties between droplet and wall film fluid are chosen. The dimensionsless film thickness δ is added to form a 3D plot, where one-and two-component experiments are combined. Existing correlations from the literature are revised regarding both interactions and their consistency is checked. The investigated range of high viscosity fluids allow us to propose an improvement of the correlation for high Oh. Our results show that the arithmetically averaged fluid properties lead to a good repartition of both one-and twocomponents interactions toward the deposition/splashing limit. They also corroborate the previous findings that an increase of δ inhibits splashing but its influence is decreasing with increasing Oh. Keywords droplet impact, thin film, two-components interaction, splashing treshold. IntroductionSingle drop impact on a thin liquid layer (i.e. wall film) covers a wide range of industrial applications like coating, printing, cooling or combustion. They are of particular interest since they lead to the ejection of secondary droplets, the so-called splashing.The investigations concerning the droplet impact on wetted walls show that for a given Reynolds number (Re), Ohnesorge number (Oh) and dimensionsless wall film thickness (δ, film thickness h over droplet diameter D), the outcome of one-component droplet impact can be determined. Roughness of the wall can be neglected in the case of 0.1 ≤ δ ≤ 1 [9], when it is completely embedded in the liquid wall film. However, drop-film interactions are affected by the use of different fluids for the droplet and the liquid film. Very little is known for this two-component interaction: the available database is still sparse and therefore the validity of proposed correlations for the deposition/splashing limit cannot be yet generalized to any type of fluid combinations. In this study, we consider a droplet impact of Newtonian fluids onto a wetted, cold, horizontal, solid surface. In the following, the denomination fluid1/fluid2 means that a fluid1 droplet impacts onto a fluid2 wall film and fluid1-fluid2 that both permutations were performed. This study focuses on ...

We study the vertical impact of a droplet onto a cubic pillar of comparable size placed on a flat surface, by means of numerical simulations and experiments. Strikingly, during the impact a large volume of air is trapped around the pillar side faces. Impingement upon different positions of the pillar top surface strongly influences the size and the position of the entrapped air. By comparing the droplet morphological changes during the impact from both computations and experiments, we show that the direct numerical simulations, based on the Volume of Fluid method, provide additional and new insight into the droplet dynamics. We elucidate, with the computational results, the three-dimensional air entrapment process as well as the evolution of the entrapped air into bubbles.