Turbulent silicon melt flows are studied in large diameter Czochralski crucibles under the influence of alternating, steady and combined magnetic fields. The investigations are based on the experimentally verified two-dimensional axisymmetric mathematical models. The influence of steady, alternating and combined magnetic fields on the flow pattern and temperature held is investigated. Global heat transfer and melt flow calculations are coupled and the influence of melt convection on the interface shape is studied and compared with experimental data.