Modeling of turbulent transport and solidification during continuous ingot casting

Abstract

Continuous ingot casting is an important processing technology for many materials. Under most practical circumstances, turbulence plays a critical role which, along with transport mechanisms such as buoyancy, surface tension, and phase change, is responsible for the quality of the end products. A modified turbulence model based on the standard k- e two-equation closure is proposed and applied to predict the phase change and convection-diffusion characteristics during titanium alloy ingot casting in an electron beam melting process. In conjunction with an adaptive grid computational technique, solutions of the coupled mass continuity, momentum, energy, and turbulence transport have been obtained in the context of the enthalpy formulation. Effects of casting speed and gravity on solidification and convection characteristics have been investigated and compared to ones obtained previously with a simple zeroequation turbulence model. The present turbulence model predicts that the mushy zone is generally of substantial thickness as a result of the convection effect, that the solidus line has a high curvature, and that the temperature gradient close to the solidus line is higher than elsewhere. Under all conditions, the turbulence structure largely reflects the combined influence of convection and energy input by the electron beam and the superheated feeding material from the top surface. The numerical results have been compared with an experimentally determined pool profile from a casting ingot.