Magnetisches Rühren beim Stranggießen von Stahl: Simulation mit FLUENT
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The velocity field inside the fluid core is important for the solidification structure and high velocities along the solidification front are appreciated. In-mould electromagnetic stirring is used to enhance the transition from columnar to dendritic solidification to get a finer structure for the end product. The rotary effect of the electromagnetic stirring can not be measured or observed in the process because of the hazardous environment. Physical models using water instead of liquid steel are used for the normal casting process, but are not capable to consider electromagnetic stirring, because of water’s low electric conductivity. On the other side, metals which are liquid at low temperatures are expensive and non-transparent - making it difficult for measuring. So, numerical simulations are nearly irreplaceable means of getting an insight into the flow structures with electromagnetic stirring. In this paper two methods for simulating the electric stirring inside the mold are presented. The first one is a semi-empirical model which uses an analytical result for the Lorentz-force via UDF-source-terms. The second approach considers the full coupling between the magnetic field and the velocity field using the Fluent MHD-Module. Because the magnetic field is unsteady, a transient simulation is mandatory. First, simple test cases simulated with the MHD-Module show extremely slow convergence. Thus, different strategies are employed for the simulation of the strand: the solution calculated by the method with semi-empirical Lorentz force densities is used as an initial solution at the start of the computation. The induced magnetic fields are saved after each time step to be used after one revolution as a better initial solution than the field from the previous time-step.