Transient study of turbulent flow and particle transport during continuous casting of steel slabs

This study investigates turbulent flow and impurity-particle transport during continuous casting of steel slabs, which are important to product quality. Velocities in the nozzle and mold regions were computed using Large Eddy Simulation (LES). The accuracy of these complex flow simulations was examined by comparing with measurements such as Particle Image Velocimetry (PIV) and hotwire anemometry. The computed time-averaged and rms velocities agreed reasonably with the measurements. The evolution of transient flow structures was investigated along with the corresponding time scales. Oscillating flow in the mold region caused asymmetrical particle transport. Interactions between flow in the two halves of the mold were found to cause large velocity fluctuations on the top surface. The differences between flow in a steel caster and in its corresponding water model were also quantified.; Using the computed three-dimensional time-dependent flow velocities, the motion and capture of impurity particles during continuous casting were simulated using a Lagrangian approach. A criterion was developed to model particle pushing and capture by the solidifying shell and was incorporated into the particle transport model. The criterion was validated by reproducing experimental results in different systems. The particle transport model was applied to a full-scale water model and reproduced the measured particle removal fractions of 27 +/- 5% for 0--10s and 26 +/- 2% for 10--100s. The model was then applied to simulate the motion and capture of slag particles in a thin-slab steel caster. The magnitudes of the steady and unsteady forces acting on the particles. The simulations found that only about 8% of the small particles (10 and 40 microns) were safely removed by the top surface slag layer. However, a higher removal fraction of about 12--70% was found for the larger particles (100--400 microns). The computational results were processed to predict the ultimate distribution of impurity particles in the solid thin-slab. The results of this work confirm the important role of flow transients in the transport and capture of particles during continuous casting, and can serve as a benchmark for future simplified models.