Numerical solution of the dragout problem in film coating and gas-jet wiping processes
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The withdrawal of a solid material from a liquid bath (the drag-out problem) is still a very active subject of research. Indeed, coating of solids is of high interest in many industrial applications. The technological challenge is to control the homogeneity and thickness of the coated layers under various flow and capillary regimes in presence of gravity and inertia effects. In the context of the drag-out, the gas-jet wiping process helps to control and to reduce the thickness of a liquid film deposit on flat plate which is withdrawn at certain velocity. The capillarity plays a crucial role on the stability and the thickness of the film. The solution of the hydrodynamics problem for regular boundary conditions at interfaces and under certain flow regimes has been proposed in 1942 by Landau and Levich [1], almost a century later. The motivations to still work on the subject comes from the variety and the complexity of liquid-air and solid interface properties, and from the process condition involved (a turbulent air jet impacting the liquid film) which play a crucial role to rationalize the quantity of liquid deposited on the solid. The numerical solution of such problems is extremely challenging, because of the variety of space time scales of the phenomenon, multi-separate phase modelling, accuracy and cost of calculations. Here we consider the gas liquid solid interaction including the effects of surface tension, wettability, gravity, inertia and turbulence. The numerical framework relies on a monolithic approach with immersed embedded interfaces which motion are calculated with a local convected level set method [2]. The geometries are interpolated and can contribute to the numerical error and control in the a posteriori error estimator. This approach favours the full usage of anisotropic adaptive meshing techniques providing an optimal capture of moving interfaces, whatever is the complexity of the geometries. The multi-fluid-solid flow solver designed for unstructured anisotropic meshes enters in the framework of continuous stabilized finite element method (residual based stabilisation). 2d and 3d Benchmarks of the drag-out problems from low to high speed of withdrawing will be proposed in relation to experimental data of industrial interest. New complete simulations including the air-jet impingement of the liquid will be proposed and discussed.