Dynamics of the jet wiping process via integral models

Mendez, Miguel Alfonso; Gosset, Anne; Scheid, Benoît; Balabane, Mikhaël; Buchlin, Jean‐Marie

doi:10.1017/jfm.2020.1075

Cited by 13 publications

(42 citation statements)

References 94 publications

(137 reference statements)

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“…2019), the jet-wiping (or air-knife) coating process in which impinging jets of air are used to control the thickness of a fluid film on a moving substrate (Barreiro-Villaverde, Gosset & Mendez 2021; Mendez et al. 2021), while a film of fluid on a rotating cylinder in an airflow is a key component of a recently proposed method for applying pesticides to crops using minimal amounts of chemical and with minimal drift (Newell & Viljoen 2019).…”

Section: Introductionmentioning

confidence: 99%

Coating flow on a rotating cylinder in the presence of an irrotational airflow with circulation

2021

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A detailed analysis of steady coating flow of a thin film of a viscous fluid on the outside of a uniformly rotating horizontal circular cylinder in the absence of surface-tension effects but in the presence of a non-uniform pressure distribution due to an irrotational airflow with circulation shows that the presence of the airflow can result in qualitatively different behaviour of the fluid film from that in classical coating flow. Full-film solutions corresponding to a continuous film of fluid covering the entire cylinder are possible only when the flux and mass of fluid do not exceed critical values, which are determined in terms of the non-dimensional parameters $F$ and $K$ representing the speed of the far-field airflow and the circulation of the airflow, respectively. The qualitative changes in the behaviour of the film thickness as $F$ and $K$ are varied are described. In particular, the film thickness can have as many as four stationary points and, in general, has neither top-to-bottom nor right-to-left symmetry. In addition, when the circulation of the airflow is in the same direction as the rotation of the cylinder the maximum mass of fluid that can be supported on the cylinder is always less than that in classical coating flow, whereas when the circulation is in the opposite direction the maximum mass of fluid can be greater than that in classical coating flow.

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Section: Introductionmentioning

confidence: 99%

Coating flow on a rotating cylinder in the presence of an irrotational airflow with circulation

2021

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“…Although the long-wavelength nature of the undulation is reminiscent of interface instabilities in gravity-driven falling films [9][10][11] , several works 5,12,13 have shown that these do not result from an intrinsic instability of the liquid coat. On the other hand, it has been recently shown 14,15 that the liquid film is sensitive to jet disturbances such as pulsation and oscillations, if these occur at sufficiently low frequencies. The present work analyzes the origin of jet disturbances and their impact one the coating film.…”

Section: Arxiv:210316116v1 [Physicsflu-dyn] 30 Mar 2021mentioning

confidence: 99%

“…As of today, the only tools available to analyze some of the mechanisms at the origin of the undulation in galvanizing conditions are simplified integral models, recently extended by Mendez et al 15 . These models were used to derive the response of the liquid film to a set of perturbations and identify, for various operating conditions, the range of frequencies yielding the largest disturbance amplification.…”

Section: Arxiv:210316116v1 [Physicsflu-dyn] 30 Mar 2021mentioning

confidence: 99%

“…We briefly recall here the fundamentals of 2D integral models of the jet wiping process, as the simplifying assumptions made in their derivation are tested in this work. For a more extensive treatment of these models, the reader is referred to Mendez et al 15 .…”

Section: A Note On 2d Integral Modelsmentioning

confidence: 99%

“…Inserting these coefficients into the definition of the advection and the shear stress in (15) terms gives…”

Section: Reference Quantity Definition Expressionmentioning

confidence: 99%

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On the dynamics of jet wiping: Numerical simulations and modal analysis

2021

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We analyze the flow of a planar gas jet impinging on a thin film, dragged by a vertical moving wall. In the coating industry, this configuration is known as jet wiping, a process in which impinging jets control the thickness of liquid coatings on flat plates withdrawn vertically from a coating bath. We present three-dimensional (3D) two-phase flow simulations combining Large Eddy Simulation (LES) and Volume of Fluid (VOF). Three wiping configurations are simulated and the results are validated with experimental data from previous works. Multiscale modal analysis is used to analyze the dynamic interaction between the gas flow and the liquid film. In particular, we present a combination of Multiscale Proper Orthogonal decomposition (mPOD) and correlation analysis. The mPOD is used to identify the dominant travelling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet. This allows for revealing a two-dimensional (2D) mechanism for wave formation in the liquid coat. Finally, we use the numerical results to analyze the validity of some of the critical assumptions underpinning the derivation of integral film models of jet wiping.

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