Abstract
Many studies have been devoted to single drop impacts onto liquid films and pools, while just a few are available about double drop or drop train impacts, despite the fact that the latter are more realistic situations. Thus, computational fluid dynamics with a volume-of-fluid approach was used here to simulate the impact of multiple drops into deep pools. The aim was to verify if multiple drop impacts significantly differ from single drops ones, and if the models available in the literature for the crater depth in the case of single impacts are reliable also for the multiple drop cases. After validation against experimental data for single and double drop impacts, simulations for four to 30 drops, with a diameter of 2.30 mm, impact velocities 1.0, 1.4, 1.8, and 2.2 m/s, and random initial positions in the domain were performed. The results showed that the time evolution of the crater depth for multiple impacts is similar to the single drop case during the inertial phase, while the following behavior is very different. Consequently, the available models for the maximum crater depth during single drop impacts can still predict the upper and lower bounds of the values of the crater depth during multiple drop impacts within 5% deviation.
Highlights
Many phenomena, both of natural and technological interest, involve the interaction between liquid drops and an interface, in most cases between a solid and a gas or a liquid and a gas
Among the many parameters that characterize the crater, expanding and receding after the drop impact, the crater depth was selected as the quantity of interest for this study, even if it must be kept in account that the drop water was transported towards much lower depths than the crater’s bottom [8,9,59])
Mesh independence was verified by performing numerical simulations with mesh sizes between 72,200 and 7,166,250 cells, as shown in Figure 5 for the case of the single drop impact at 1.4 m/s
Summary
Both of natural and technological interest, involve the interaction between liquid drops and an interface, in most cases between a solid and a gas or a liquid and a gas. The interaction may be mechanical, thermal, or chemical, and it may start with the generation of the drop on the interface (as during condensation) or with the impact of the drop onto the same. In the latter case, the impact velocity may be low (down to practically zero when the drop is gently deposed) or high, normal, or oblique. A first example is obviously rain, with its effects on the Earth’s water surfaces (oceans, seas, lakes, rivers, etc.) and on, e.g., fields, buildings, monuments, planes, and wind turbines This happens in many other scenarios, e.g., internal combustion engines, firefighting systems, surface cooling, spray painting, inkjet printing, pesticide distribution in agriculture, and blood sprays in crime scenes. The importance of a deep understanding of this phenomenon is evident, which is far from being a simple one, up to the point that despite more than a century of investigation it is still not fully explained
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