Numerical and Experimental Study of the Meniscus Vortex Core in a Water Model of Continuous Casting Mold
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TRODUCTION
IN a continuous casting mold, the mold powder is supplied on the top surface of the molten steel. It forms a liquid slag layer, as it melts on the top, which not only prevents the oxidation of the molten steel meniscus, but also acts as a lubricant between the mold and the molten steel.[1] However, the slag entrainment into the molten steel can lead to serious defects in steel products, such as sliver, scab, and blister.[2] Many studies have investigated the reason for the slag entrainment and the related preventive measures; the strong meniscus velocity and its fluctuation have largely been pointed out as the main causes.[36] Therefore, various measuring technique have been developed to more accurately gauge the meniscus velocity.[3] In terms of the fluctuation in the meniscus velocity, a flow asymmetry in the mold has also been reported as an important trigger for the flow fluctuation. The effects of nozzle clogging, sliding gate, and off-centered SEN are JONG HUI LEE is with the Department of Mechanical Engineering, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Republic of Korea. SANGWOO HAN and HYUN-JIN CHO are with the Steelmaking Research Group, Technical Research Laboratories Pohang Research Lab, POSCO, 6261 Donghaeanro, Namgu, Pohang, Gyeongbuk 37859, Republic of Korea, and IL SEOUK PARK is with the School of Mechanical Engineering, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted June 9, 2020; accepted October 9, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
regarded as a potential cause of the flow asymmetry.[4] However, the computational fluid dynamics (CFD) simulations and water model tests have shown that the flow asymmetry may appear even under complete symmetry in geometries.[5,6] The instantaneous flow continues to oscillate periodically, although the time-averaged velocity distribution is in good symmetricity. Another important factor for the slag entrainment, which could not be fully addressed by only the shear stress effect, is the vortexing flow (meniscus vortex) on the top.[7,8] Meniscus vortices have been reported to largely occur near the SEN, and it can be moved far from the SEN by argon gas injection.[9] Anyway, more basically the meniscus vortexing flows are created by the impingement of two streams approaching from opposite sides or the sudden development of a boundary layer by the wall friction effect. At the center of a vortexing flow, a very strong swirl velocity is formed by the angular momentum conservation, and the center would be a singular point; Sohn et al. explained this with the Ekman spiral suction and Taylor vortex stacking structure.[10,11] Therefore, if the vortexing flow meets a downward flow circulating in the upper region of the mold, the downward flow can be significantly accelerated. The flow environments favorable to the slag entrainment could be accomplished by the meniscus vortex. Various experimental[4,7,8,12,13] and numerical studies[6,7,14,15] have been conducte
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