Some experiences with the numerical simulation of Newtonian and Bingham fluids in dip coating

• A FVM-VOF numerical method was applied to dip-coating flows under several dynamic conditions.
• Accurate simulations were performed using Newtonian and Bingham fluids for flat plate and wire coating.
• The effect of high inertia forces on the free surface are adequately captured.
• Clear exhibit of free surface waviness and tendency to ingest air for cases with a cusp was demonstrated.
• Calculations demonstrate that fluid recirculation below cusp mentioned before does not exist.

The dip-coating process is simulated numerically for Newtonian and Bingham fluids with a particular emphasis on finding the free surface location under different sets of conditions. The main focus of the simulations is the evaluation of the Finite-Volume Method (FVM) combined with the Volume-Of-Fluid (VOF) technique embedded in the commercial code (Fluent), while some results are also obtained with the Finite-Element Method (FEM) using another commercial code (Polyflow). The objective is to check how well the results compare with previous results regarding the free surface location for both axisymmetric and planar geometries, and also provide new results. The numerical results were first validated against previous experimental data for the Newtonian limit case. Then numerical results were compared favourably with previous simulations available in the literature for both Newtonian and Bingham fluids. The influence of the coating fluid properties as well as surface withdrawal speed for Newtonian fluids and of the yield stress for Bingham fluids are discussed. The effect of inertia for the planar case is investigated, and the formation of the cusp and wavy shape of the free surface is analyzed.