Transient Turbulent Flow in a Liquid-Metal Model of Continuous Casting, Including Comparison of Six Different Methods
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ON of fluid flow in the continuous casting process is important to minimize defects in steel products. Turbulent fluid flow in the submerged entry nozzle (SEN) and the mold are the main causes of entrainment of slag inclusions and the formation of surface defects.[1] Computational models combined with physical models are useful tools to study the complex turbulent flow in these systems.[2] Reynolds-averaged Navier–Stokes (RANS) models and water models are among the most popular techniques to analyze these systems.[3–7] Relatively few studies have exploited accurate fine-grid large eddy simulations (LES) to quantify transient flow in the nozzle and mold of continuous casting of steel,[8–13] and even fewer have applied filtered unsteady RANS (URANS) models.[14] Yuan et al.[8] combined LES and particle image velocimetry (PIV) measurements in a 0.4scale water model. The LES predictions matched well with the measurements. Transient oscillations were observed between two different flow patterns in the upper region—a wobbling stair-step downward jet and a jet that bends midway between the narrow face and the SEN. Long-term flow asymmetries were observed in the R. CHAUDHARY, Ph.D. Student, and B.G. THOMAS and S.P. VANKA, Professors, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Contact e-mail: [email protected] C. JI, Ph.D. Student, is with the School of Metallurgy & Ecology Engineering, University of Science & Technology Beijing, Beijing 100083, P.R. China. Manuscript submitted April 1, 2011. Article published online May 17, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
lower region of the mold. Interaction of the flow from the two sides of the mold caused large velocity fluctuations near the top surface. Ramos-Banderas et al.[9] also found that LES model predictions agreed well with instantaneous velocity field measurements using digital PIV in a water model of a slab caster. Flow changed significantly because of vertical oscillations of the jet. Turbulence induced natural biasing without the influence of any other factors such as slide-gate, gas injection, or SEN clogging. Instantaneous velocity showed that periodic behavior and frequencies of this behavior were reported increasing with flow rate. In another work, Yuan et al.[10] performed LES and inclusion transport studies in a water model and a thin slab caster. Complex time-varying structures were found even in nominally steady conditions. The flow in the mold switched between double-roll flow and complex flow with many rolls. Zhao et al.[11] performed LES with superheat transport and matched model predictions with plant and full-scale water model measurements. The jet exiting the nozzle showed chaotic variations with temperature fluctuations in the upper liquid pool varying ± 4 C and heat flux ± 350 kw/m2. Adding the static-k subgrid scale (SGS) model had only minor effects. Qian et al.[12] employed LES with direct current magnetic field effects in a slab continuous casting process. A new vortex brake was
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