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Continuous casting - comparison between numerical simulation and experimental measurement EPM-MADYLAM Y.Delannoy, O.Widlund, J.Etay Presented by Y.Fautrelle

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Continuous casting : simulation / experiment 2 EMBR for steel C.C. Continuous casting of steel Vertical pulling velocity ~1-2 m/mn (2cm/s) Nozzle with two ports jets ~ 1m/s Control of temperature and inclusions electromagnetic actuators Electromagnetic brake (EMBR) Transverse DC magnetic field to slow down the jets Positioned at the surface level to damp level fluctuations Numerical model + validation MHD model added to Fluent® + MHD k- model Velocity measurements in a Mercury model Copper mould bending & cooling Submersed entry nozzle liquid steel pulling

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Continuous casting : simulation / experiment 3 Mercury model Design principles Reduced typical slab caster (scale 1/3) Froude similar flowrate (~casting 1m/mn) No thermal effects, no solidification Horizontal DC magnetic field up to 0.47T (centre) Available measurements Surface level fluctuations (not used here) Vertical velocity profiles v z (z,t) velocity fluctuations (not used here) mean velocity profiles V z (z) Iron yoke Hg container Horizontal DC field DC coil Hg in Hg out Nozzle

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Continuous casting : simulation / experiment 4 Experimental profiles Vz(z) Measurement conditions In the midplane (y=0) – 2D flow if B>0 Near the nozzle jet position (V z max) Near the small face impact (V z =0) Effect of B Fluctuation reduction (in general) Apparent acceleration of the “mean” jet (due to stabilization?) then braking Increase of downward flow near the nozzle Raise of the jet position and “impact” (gradient of V z ) poles of electromagnet Free surface z,V z x Measurement lines

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Continuous casting : simulation / experiment 5 Fluid flow model Reynolds Averaged Navier-Stokes (RANS) + Lorentz force f=jxB K- turbulence model + source terms due to anisotropy ( ) 2-layer wall functions on walls, free slip on surface, V z imposed at outlet Electromagnetic model No convection of B (R m <<1) B imposed from measurements Electrical current from potential: j= (- +UxB) Potential equation from current conservation: 0= .( )- .(UxB) Neuman conditions on (insulating walls) + reference =0 at inlet Turbulence anisotropy equation Deduced from transport of triple correlations Source term due to B Transport by the flow and turbulent diffusion Non linear sink (return to isotropy) Domain and mesh MHD interaction: internal / external flow around nozzle Whole domain (no symmetry), cells Numerical model

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Continuous casting : simulation / experiment 6 MHD bidimensionnalisation B=0 B max Vertical vortices stagnation line 2D flow 3D jet flow Impact point Impact line

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Continuous casting : simulation / experiment 7 Jets and recirculations Effect of B “Brakes” the jet because of 2D spreading Symmetrisation of the upper loops Raise the level of jets Importance of the internal flow No Hartmann flow in the nozzle because of a leak of current across the ports High current flowing to the external flow Current closure increase the downward velocity around the nozzle Asymetry Always present even if fine convergence More pronounced with the real nozzle (“conical” bottom) nozzle with hole used in the calculations B=0 B max No vector drawn if |V|>0.5m/s

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Continuous casting : simulation / experiment 8 Comparison Quantitative aspects Differences num-exp even without field Real geometry of the nozzle to be introduced Effect of B well reproduced Raise the jet Deforms the profile near the small face Increase the downwards velocity near the nozzle B=0 B max x=4cmx=20cm

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Continuous casting : simulation / experiment 9 Conclusion and perspectives Experimental results available for validation Numerical model available for MHD in complex geometry Validation of the numerical model for the effect of B Real geometry of the nozzle to be introduced Stable and unstable asymetry to take into account Prediction of fluctuations with and without B?

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