Study of Transient Flow Structures in the Continuous Casting of Steel

In continuous casting of steel, plant observations have found that many serious quality problems are directly associated with the flow pattern in the mold. Previous studies have generated understanding mainly through numerical simulations using timeaveraged turbulence models. However, many problems are intermittent and the essential transient nature of the flow may be important to their formation. To obtain further understanding of these important transient turbulence processes, this project aims to directly compute the evolution and dynamics of the large scale turbulence structures. Accurate numerical schemes and parallel computers are being applied to solve the governing fluid flow equations using a Large-Eddy Simulation (LES) approach. Computations are also performed using traditional k-ε models in order to evaluate their accuracy and to examine more cases. The ultimate goal is to generate deeper understanding of how costly defects form and to find improvements in design and operating conditions that can avoid them. Introduction: Continuous casting is the predominant way by which steel is produced in the world. Continued viability of the high-volume-lowprofit-margin steel industry depends upon improved efficiency and consistent quality of the steel production. Steel scrapped due to defects is both costly and wasteful of energy. Plant observations have found that many serious quality problems are directly associated with the flow pattern in the mold . Defects caused by non-optimal fluid flow are even more important to the nearernet-shape thin-slab casting processes, which are starting to transform the industry . Some understanding of this flow region can be obtained through numerical simulations which use time-averaged turbulence models. The next step to obtain deeper insight into the transient turbulent aspects of this process is to directly compute the evolution and dynamics of the large-scale turbulence structures. The current research is concerned with such computations, using accurate numerical schemes and parallel computers to solve the governing fluid flow equations. A schematic of part of the continuous casting process is depicted in Figure 1. Steel flows through the “tundish,” and then it exits down through a ceramic Submerged Entry Nozzle (SEN) and into the mold. Here, the steel freezes against the water1 Today, US produces around 80 million tons of steel per year. The net cost per ton of scrapping is about $100 per ton. Even if a fraction of one percent of scrap is avoided due to improving the process, the savings is still significant.