Coupling 3D CFD of Air Knife Jets with an Analytical Model for Coating Thickness Prediction and Operating Window Definition in Hot-Dip Galvanizing

A coupled modeling framework is developed to predict coating thickness after air knife wiping in hot-dip galvanizing. A 3D large eddy simulation (LES) using the WALE sub-grid scale (SGS) model is performed to resolve the jet impingement on the moving strip. Time-averaged wall static pressure pωy and wall shear stress τωy along the strip direction are extracted and used as driving inputs for a thin film model. Starting from the continuity and momentum equations, a lubrication-type formulation is derived, leading to a local cubic equation for film thickness h(y) that accounts for both pressure gradient and gravity. A coupling workflow is established to preprocess the LES wall signals and compute the final coating thickness hfinal. Parametric sweeps of inlet total pressure P0 and the knife-to-strip distance H are employed to construct operating window maps. The predicted trends show that increasing P0 or decreasing H intensifies wall loading and reduces hfinal, while the operating window boundary is governed by the balance between the gas-induced shears. Representative results, including peak wall loading and thickness ranges, are reported for industrially relevant operating conditions.