Aspect Ratio Effects on Fluid Flow Fluctuations in Rectangular Cavities
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UCTION
IN continuous steel casting, liquid steel flows through a submerged nozzle into a mold. Figure 1 shows schematics of the top of the continuous casting mold. In the center a submerged nozzle is present, and W and T indicate the width and the thickness of the mold, respectively. The submerged nozzle is of the bifurcated type, expelling two (nearly) horizontal jets in opposite directions. Configurations encountered in continuous casting, based on the width-to-thickness ratio (W/T) of the cavity, are billet casting (W/T 1), slab casting (4 < W/T < 10), and thin slab casting (W/T > 15). A slag layer is present on top of the liquid steel to prevent oxidation of the steel and to provide thermal insulation. Flow instabilities and resulting instabilities of the steel/ slag interface can have a large influence on the entrainment of slag, which has a detrimental impact on the steel quality. In lab experiments, the continuous casting process is often modeled using water, with a free air/water interface, as a working fluid (e.g., References 1 through 3). The suitability of using scaled cold water models in the study of continuous casting was discussed by Chaudhary et al.[4] The main advantage of using water is that it is RUDI KALTER and BERNHARD W. RIGHOLT, Ph.D. Students, MARK J. TUMMERS, Assistant Professor, JEROEN B. WEFERS BETTINK, Student, SASA KENJERE, Associate Professor, and CHRIS R. KLEIJN, Professor are with the TU Delft, Delft, The Netherlands. Contact e-mail: [email protected] Manuscript submitted May 2, 2014. Article published online July 11, 2014. 2186—VOLUME 45B, DECEMBER 2014
transparent, so optical experimental techniques like laser Doppler anemometry (LDA), particle image velocimetry (PIV), and particle tracking velocimetry (PTV) can be used. The kinematic viscosity of water and liquid steel are approximately the same (within 20 pct, [5] ), so Reynolds and Froude similarity is achieved when a near full-scale replica of a caster mold is employed in the experiments. From studies of water flowing from submerged bifurcated nozzles into rectangular cavities, different kinds of instabilities of the free surface have been recognized, resulting in an incomplete picture of the nature of flow instabilities in these configurations. Honeyands and Herbertson[1] reported self-sustained oscillations with a frequency of 0.2 Hz in a cavity with W/T = 25. On top of that they found a less pronounced natural mode oscillation of 0.7 Hz. Torres-Alonso et al.[3] report a stable free surface profile with a periodic distortion of this stable profile with a frequency of 0.01 Hz in a cavity with W/T = 25. Jeon et al.[6] report 0.8 Hz oscillations in the natural mode for a cavity with W/T = 13.5. In our previous study of flow from a bifurcated nozzle into a rectangular cavity with W/T = 18, a flow regime map was reported with three different flow regimes depending on the nozzle depth and the inlet velocity.[7] One of the flow regimes was a self-sustained oscillation of the two jets emerging from the bifurcated nozzle. The self-sustained jet
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