Mathematical description of flow and heat transfer in continuous casting machines

The aim of this RFCS contract is to improve the simulation possibilities of existing CFD codes by further development, especially with regard to bubble or free surface behaviours and thermo-mechanical prediction in continuous casting mould. An important set of data inside a water model is obtained for free surface, velocity and oscillation frequencies. With standard unsteady realisable k-ε, a main unsteady flow pattern is reproduced; both jet flapping (~ 0.05 Hz in water model) and free surface fluctuations (~ 0.5 Hz in water model) are correctly simulated by CFD. With a steady state assumption without any free surface deformation, calculations based on pressure distribution at free surface are qualitatively in agreement with measurements. This simple method can be used for initial evaluation of free surface. Nevertheless, unsteady calculations with direct simulation of free surface deformation provide better results. Break-up and coalescence laws are proposed; they provide good quantitative results for bubble size distribution in water model. To study the potentiality of some electromagnetic actuators to improve flow stability in the mould, a rotary electromagnetic system, which creates flow rotation in the nozzle, is tested. Water model experiments and calculations clearly indicate an improvement in flow stability. A novel methodology for linking two commercial software programmes (FluentTM and AbaqusTM) is also proposed. When coupling is converged, the most interesting post-processed variables are: fluid flow for the steel and water; temperature fields in steel, mould and water; shell thickness and mould powder evolution; stress-strain history for each location of the shell; together with gap generation between mould and steel.