Computational and experimental study of turbulent flow in a 0.4-scale water model of a continuous steel caster
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INTRODUCTION
TURBULENT flow in the mold region of continuous steel casters is associated with costly failures (e.g., shell-thinning breakout) and the formation of many defects (e.g., slivers) by affecting important phenomena such as top-surface-levelfluctuations and the transport of impurity particles and superheat.[1–4] Understanding the unsteady flow structures in this process is an important step in avoiding failures and decreasing defects. Unfortunately, because of the high temperature (1800 K) of superheated steel, it is difficult to conduct velocity measurements directly in molten steel.[5] However, due to the nearly equal kinematic viscosities of molten steel and water, water models have been extensively used to investigate the flow in steel casters.[6–11] The dimensions and operating conditions of a water model are usually chosen to have geometry and Froude number (or sometimes Reynolds number) similarities[12] with the actual steel caster. Figure 1(a) shows an example of a scaled water model.[9,13] The walls of the tundish, the nozzle, and the mold of a water model are usually made of transparent plastic plates. The mold side walls are sometimes curved to represent the tapering shape of the internal liquid cavity within the solidifying steel shell. A slide gate (Figure 1(a)) or stopper rod is used to control the flow rate by adjusting the opening area in order to achieve the desired casting speed (defined as the downward withdrawal speed of the shell in an actual steel caster). Water flows downward from the tundish, passes through the nozzle, enters the mold cavity, and exits from
QUAN YUAN, Ph.D. Candidate, S.P. VANKA, Professor, and B.G. THOMAS, W. Grafton and Lillian B. Wilkins Professor, are with the Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Contact e-mail: [email protected] SIVARAJ SIVARAMAKRISHNAN, Ph.D. Candidate, is with the Biomedical Engineering Department, Northwestern University, Evanston, IL 60208. Manuscript submitted July 23, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
outlet ports near the bottom. It should be mentioned that two main differences exist between a water model and its corresponding steel caster. First, in the mold region, the no-slip solid wall of a water model does not represent the solidification occurring at the shell front. Second, a water model has a horizontal bottom plate with outlet ports, while in a continuous steel caster, molten steel flows into a tapering section resulting from the solidification. Despite these differences, however, our recent studies have confirmed that the velocity field in a water model generally agrees with that in a steel caster, especially in the top region.[14] One of the advantages of a water model is that its transparent walls allow flow visualization such as dye injection[14,15] (Figure 19) and the penetration of laser light. This enables the use of accurate and nonintrusive optical laser velocimetry techniques.[16] Two typical methods are laser-doppler veloci
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