The review deals with drop impacts on thin liquid layers and dry surfaces. The impacts resulting in crown formation are referred to as splashing. Crowns and their propagation are discussed in detail, as well as some additional kindred, albeit nonsplashing, phenomena like drop spreading and deposition, receding (recoil), jetting, fingering, and rebound. The review begins with an explanation of various practical motivations feeding the interest in the fascinating phenomena of drop impact, and the above-mentioned topics are then considered in their experimental, theoretical, and computational aspects.

Drop Impact Dynamics: Splashing, Spreading, Receding, Bouncing ...

The performance of the open source multiphase flow solver, interFoam, is evaluated in this work. The solver is based on a modified volume of fluid (VoF) approach, which incorporates an interfacial compression flux term to mitigate the effects of numerical smearing of the interface. It forms a part of the C + + libraries and utilities of OpenFOAM and is gaining popularity in the multiphase flow research community. However, to the best of our knowledge, the evaluation of this solver is confined to the validation tests of specific interest to the users of the code and the extent of its applicability to a wide range of multiphase flow situations remains to be explored. In this work, we have performed a thorough investigation of the solver performance using a variety of verification and validation test cases, which include (i) verification tests for pure advection (kinematics), (ii) dynamics in the high Weber number limit and (iii) dynamics of surface tension-dominated flows. With respect to (i), the kinematics tests show that the performance of interFoam is generally comparable with the recent algebraic VoF algorithms; however, it is noticeably worse than the geometric reconstruction schemes. For (ii), the simulations of inertia-dominated flows with large density ratios yielded excellent agreement with analytical and experimental results. In regime (iii), where surface tension is important, consistency of pressure–surface tension formulation and accuracy of curvature are important, as established by Francois et al (2006 J. Comput. Phys. 213 141–73). Several verification tests were performed along these lines and the main findings are: (a) the algorithm of interFoam ensures a consistent formulation of pressure and surface tension; (b) the curvatures computed by the solver converge to a value slightly (10%) different from the analytical value and a scope for improvement exists in this respect. To reduce the disruptive effects of spurious currents, we followed the analysis of Galusinski and Vigneaux (2008 J. Comput. Phys. 227 6140–64) and arrived at the following criterion for stable capillary simulations for interFoam: where . Finally, some capillary flows relevant to atomization were simulated, resulting in good agreement with the results from the literature.

https://iopscience.iop.org/article/10.1088/1749-4699/5/1/014016/pdf

Evaluating the performance of the two-phase flow solver interFoam

Cough generated infectious aerosols are of interest while developing strategies for the mitigation of disease risks ranging from the common cold to SARS. In this work, the velocity field of human cough was measured using particle image velocimetry (PIV). The project subjects (total 29) coughed into an enclosure seeded with stage fog. Cough flow velocity profiles, average widths of the cough jet, and maximum cough velocities were measured. Maximum cough velocities ranged from 1.5 m/s to 28.8 m/s. The average width of all coughs ranged between 35 to 45 mm. Wide variability in the data suggests that future cough simulations consider a range of conditions.

https://www.tandfonline.com/doi/pdf/10.1080/02786826.2010.542785

Particle Image Velocimetry of Human Cough

Advances and challenges in explaining fuel spray impingement: How much of single droplet impact research is useful?

We present the results of a combined experimental and theoretical investigation of the normal impact of hydrophobic spheres on a water surface. Particular attention is given to characterizing the shape of the resulting air cavity in the low Bond number limit, where cavity collapse is driven principally by surface tension rather than gravity. A parameter study reveals the dependence of the cavity structure on the governing dimensionless groups. A theoretical description based on the solution to the Rayleigh–Besant problem is developed to describe the evolution of the cavity shape and yields an analytical solution for the pinch-off time in the zero Bond number limit. The sphere's depth at cavity pinch-off is also computed in the low Weber number, quasi-static limit. Theoretical predictions compare favourably with our experimental observations in the low Bond number regime, and also yield new insight into the high Bond number regime considered by previous investigators. Discrepancies are rationalized in terms of the assumed form of the velocity field and neglect of the longitudinal component of curvature, which together preclude an accurate description of the cavity for depths less than the capillary length. Finally, we present a theoretical model for the evolution of the splash curtain formed at high Weber number and couple it with the underlying cavity dynamics.

/pdf/water-entry-of-small-hydrophobic-spheres-1il6tm4suh.pdf

Water entry of small hydrophobic spheres

This paper reports on an experimental study of the impact of water drops on thin liquid films. The morphology of the impact was studied by still photography, and quantitative results were obtained by a proper image analysis technique. The time evolution of various parameters like the crown diameter, the crown height, and the secondary drop diameters are reported, and these experimental parameters are correlated and compared to available theoretical models. A particular set-up of the acquisition system allowed us to photograph the splash from below the solid wall, allowing the first estimation of the crown thickness and the total number of jets protruding from the crown rim as a function of time. The results indicate that, for the range of the parameters investigated, there is not a strong dependence on the film thickness. The evolution of the crown height depends on the impact Weber number, whereas its growing velocity and the crown thickness evolution are almost independent of Weber number.

S. Zhdanov

Papers

The role of time in single drop splash on thin film