Closing a single nozzle or multiple nozzles for a temporary casting operation (fewer strands casting) was common in a tundish due to insufficient molten steel or equipment failure. However, nozzle clogging usually happens under the situation of fewer strands casting. Hence, a temperature deviation index was introduced to characterize the temperature stratification of molten steel for a large capacity tundish, and a new calculation method of residence time curve was used to describe the different flow types of molten steel at each outlet. Based on hydraulics experiment and numerical simulation, important parameters of present case and modified case were compared. Under the situation of fewer strands casting, the proportion of internal-recycle flow after modification decreased from 30.68% to 24.55%; the standard deviation of the response time reduced from 27.59 to 13.16, and the interquartile range of temperature deviation index changed from 0.89 to 0.27.

A multiphase numerical simulation of the steel-slag flow was established by using the volume of fluid (VOF) model to study the effect of different turbulence inhibitors on the improvement of the steel-slag flow in the tundish. The steel-slag interface fluctuation was studied by vorticity magnitude and transient fluctuation change. A prediction model of residence time distribution (RTD) curve was established based on mathematical simulation and the error of prediction model can be controlled below 6% by comparing with the hydraulic results. The results show that jet flow into the tundish generated very different flow patterns. Case 1 produced a double-roll flow pattern and case 2 produced a four-roll flow pattern in the impact area. The ratio of vorticity magnitude above 1.00 s−1 near the ladle shroud was 2.60% in case 1 and the ratio of vorticity magnitude above 1.00 s−1 near the ladle shroud was 13.15% in case 2, which indicates case 2 increased the possibility of slag entrainment via the upward flow mechanism and shear layer instability. Surface velocity fluctuations in case 2 were much more severe near the ladle shroud. The thickness of the slag layer was 60 mm, the interface fluctuation towards surface in case 2 was close to 20 mm. Meanwhile, case 1 involved very small volume-fraction contours near interface. The turbulence inhibitor with internal ripples (case 1) showed a better optimization effect and the results could provide a theoretical basis for the selection of a suitable turbulence inhibitor for the 66-ton T-type tundish.