Abstract <p>A numerical method utilizing the multi-fluid VOF model was validated to accurately simulate macroscopic multiphase flow in an SKS furnace, providing a reliable reference for gas-slag-matte flow field simulations in similar industrial vessels. Using this validated model, a CFD simulation of full-scale SKS furnace multiphase flow was conducted under consistent operating conditions, focusing on agitation performance across varying slag viscosities and slag layer thicknesses. The study reveals that changes in slag viscosity and layer thickness significantly impact bath agitation efficiency, leading to reduced flow circulation area with higher viscosity and thicker slag layers. Moreover, with the variation of slag viscosity, the slag wall shear stress was found to be influenced by multiple factors, and is not suggested to be estimated simply by a single factor. Given that all variables and parameters fall within common industrial ranges, these simulation results provide enhanced understanding of SKS furnace operational dynamics and optimizing slag physical properties in SKS furnaces and similar industrial vessels.</p> Graphical Abstract <p></p>