Study of transient flow and particle transport in continuous steel caster molds: Part I. Fluid flow
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9/26/04
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Study of Transient Flow and Particle Transport in Continuous Steel Caster Molds: Part I. Fluid Flow QUAN YUAN, BRIAN G. THOMAS, and S.P. VANKA Unsteady three-dimensional flow in the mold region of the liquid pool during continuous casting of steel slabs has been computed using realistic geometries starting from the submerged inlet nozzle. Three largeeddy simulations (LES) have been validated with measurements and used to compare results between full-pool and symmetric half-pool domains and between a full-scale water model and actual behavior in a thin-slab steel caster. First, time-dependent turbulent flow in the submerged nozzle is computed. The time-dependent velocities exiting the nozzle ports are then used as inlet conditions for the flow in the liquid pool. Complex time-varying flow structures are observed in the simulation results, in spite of the nominally steady casting conditions. Flow in the mold region is seen to switch between a “doubleroll” recirculation zone and a complex flow pattern with multiple vortices. The computed time-averaged flow pattern agrees well with measurements obtained by hot-wire anemometry and dye injection in fullscale water models. Full-pool simulations show asymmetries between the left and right sides of the flow, especially in the lower recirculation zone. These asymmetries, caused by interactions between two halves of the liquid pool, are not present in the half-pool simulation. This work also quantifies differences between flow in the water model and the corresponding steel caster. The top-surface liquid profile and fluctuations are predicted in both systems and agree favorably with measurements. The flow field in the water model is predicted to differ from that in the steel caster in having higher upward velocities in the lower-mold region and a more uniform top-surface liquid profile. A spectral analysis of the computed velocities shows characteristics similar to previous measurements. The flow results presented here are later used (in Part II of this article) to investigate the transport of inclusion particles.
I. INTRODUCTION
TURBULENT flow during the continuous casting of steel is important, because it influences critical phenomena that affect steel quality. These include inclusion/bubble transport and entrapment,[1,2,3] the transport and dissipation of superheat,[4] the shape and fluctuations of the top-surface level,[5,6] and the entrainment of mold flux from velocity variations across the top surface. The continuous casting process is schematically shown in Figure 1, during which the molten steel flows into the liquid pool from the tundish through the submerged entry nozzle (SEN). The flow rate is controlled using either a stopper rod (shown in Figure 1) or a slide gate that restricts the opening area. The bifurcated or trifurcated nozzle ports direct molten steel jets into the mold cavity at the desired angle, with various levels of turbulence and swirl. The watercooled mold freezes a thin solid shell, which is continuously withdrawn at t
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