Planar Jet Stripping of Liquid Coatings: Numerical Studies

In this paper, we present a detailed example of numerical study of flm formation in the context of metal coating. Subsequently we simulate wiping of the film by a planar jet. The simulations have been performed using Basilisk, a grid-adapting, strongly optimized code. Mesh adaptation allows for arbitrary precision in relevant regions such as the contact line or the liquid-air impact zone, while coarse grid is applied elsewhere. This, as the results indicate, is the only realistic approach for a numerical method to cover the wide range of necessary scales from the predicted film thickness (tens of microns) to the domain size (meters). The results suggest assumptions of laminar flow inside the film are not justified for heavy coats (liquid zinc). As for the wiping, our simulations supply a great amount of instantaneous results concerning initial film atomization as well as film thickness.Comment: 20 pages, 20 figure

Direct Numerical Simulations of pore competition in idealized micro-spall

Cavitation and micro-spall appear when a weakly compressible (or expansible) liquid is suddenly submitted to large negative pressures resulting in volume growth. After the initial phases of uniform expansion and pore opening, a longer-lasting phase of pore growth and competition appears, which is especially difficult to investigate either experimentally or numerically [Signor, PhD, 2008]. Thus this study is among the first of its kind. We present here Direct Numerical Simulations (DNS) of this latter phase for idealized conditions relevant to micro-spall: incompressible inviscid fluid, vanishing vapor pressure in cavities, ballistic uniaxial expansion, perturbed Face-Centered-Cubic arrangement of pores. Under these assumptions, the system is characterized by a single dimensionless group, the Weber number based on the number of pores per unit volume. Volume transfer between pores occurs at low enough Weber numbers, a phenomenon designated as ""pore competition"". The pore competition effect is important as it is the main phenomenon driving the evolution in time of the statistical distribution of pore sizes. Small pores shrink and eventually disappear as their volume is transferred to large pores. Pore statistics and pressure evolution profiles can then be obtained for future modelling purposes. The simulations were performed using the volume of fluid method [Tryygvason, Scardovelli & Zaleski, Cambridge, 2011] with the mixed-Youngs-central scheme for normal vector computation and interface segment reconstruction, lagrangian explicit or ""CIAM"" advection, an original adapted first order extrapolation method in the neighborhood of the free surface, and a ghost fluid method for the pressure boundary condition on the free surface. The pressure used in the boundary condition is computed using Laplace's law, which in turn involves surface tension and curvature. Curvature is computed using the height-function method. The method was tested comparing numerical solutions to solutions of the Rayleigh-Plesset equation for oscillating bubbles. An adapted procedure is used to manage the collapsing cavities. A cavity tagging and Lagrangian tracking algorithm is used to retrieve statistics of cavity sizes

Investigating the liquid jet atomization process by multiscale analysis and numerical simulation

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Investigating the liquid jet atomization process by multiscale analysis and numerical simulation

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Towards an interpretation of the scale diffusivity in liquid atomization process: An experimental approach

WOS:000360871200054International audienceRecent investigations have presented an application of the scale entropy diffusion theory to model liquid atomization process. This theory describes multi-scale behavior by a diffusion equation of the scale entropy function. In atomization, this function is related to the scale-distribution which provides a measurement of the specific-length of the eroded liquid system according to the scale of erosion. The present paper performs a detailed description of the scale diffusion mechanism for the atomization process of a liquid jet emanating from a gasoline injector with the objective of determining the scale diffusivity parameter introduced by the diffusion theory. The 2-D description of the gasoline jet as a function of the injection pressure reveals that the scale space is divided into two regions according to the sign of the scale specific-length variation rate: The small-scale region refers to the scales that undergo an elongation mechanism whereas the large-scale region concerns the scales that undergo a contraction mechanism. Furthermore, two phases of the atomization process are identified depending on whether the elongation mechanism is governed by the jet dynamics or surface tension effects. A non-dimensional number segregating these two phases is established. During the atomization process, the contraction mechanism diffuses in the small scale region. This manifests by a temporal decrease of the scale with a zero specific-length variation. It is found that the scale diffusivity parameter can be determined from the evolution of this characteristic scale in the second phase of the atomization process. (C) 2015 Elsevier B.V. All rights reserved

Probing Liquid Atomization using Probability Density Functions, the Volume-Based Scale Distribution and Differential Geometry

International audienceThe volume-based scale distribution is the 3D extension of 2D surface-based scale distribution originally defined by Dumouchel et al. (2008). It allows characterizing the multi-scale features of shapes with complex morphology. It thus appears as an attractive metric for characterizing the primary atomization process where liquid structures are generally not spherical. On the other hand, curved surfaces such as liquid-gas interfaces can also be well represented by differential geometry and the use of intrinsic observables such as the two principal curvatures. In this study, we use results from differential geometry to build analytical bridges between the volume-based scale distribution and the geometry of the liquid-gas interface (namely the surface area, the mean and Gaussian curvatures). We also present some links between these quantities and the statistical moments of 'equivalent' systems constituted of either sheets, cylinder or droplets

Numerical simulations of pore isolation and competition in idealized micro-spall process

International audienceThe ‘micro-spall’ phenomenon is a variant of fragmentation process—or spall fracture—that is traditionally discussed in context of solid materials (metals). However it concerns situations in which the medium is fully or partially melted—be it due to kinetic impact, detonation or laser loading. The phenomenon takes place at sub-micrometer and sub-microsecond scales making it inaccessible to direct experimental observation; so far, investigations have been restricted to observations of late time “post-mortem” fragments. In this context, it becomes a viable approach to apply analysis using numerical description for fluids. This work presents such an application for an idealized rapid uniaxial (one-dimensional) system expansion. Cavitation in the medium is represented by including vacuous pores or cavities with surface tension whose growth and interaction are traced in time. The simulations reveal two main regimes of pore growth regulated by a characteristic Weber number

Planar Jet Stripping of Liquid Coatings: Numerical Studies

International audienceIn this paper, we present a detailed example of numerical study of film formation in the context of metal coating. Subsequently we simulate wiping of the film by a planar jet. The simulations have been performed using Basilisk, a grid-adapting, strongly optimized code. Mesh adaptation allows for arbitrary precision in relevant regions such as the contact line or the liquid-air impact zone, while coarse grid is applied elsewhere. This, as the results indicate, is the only realistic approach for a numerical method to cover the wide range of necessary scales from the predicted film thickness (hundreds of microns) to the domain size (meters). The results suggest assumptions of laminar flow inside the film are not justified for heavy coats (liquid zinc). As for the wiping, our simulations supply a great amount of instantaneous results concerning initial film atomization as well as film thickness

Multi-Scale Description and Analysis of Simulated Liquid Atomization Processes

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