Simulation of macrosegregation in direct-chill casting—A model based on meshless diffuse approximate method

Abstract

A multiphysics numerical model has been developed for prediction of macrosegregation in direct-chill casting. The model uses volume averaged mass, momentum, energy, and species conservation equations to simulate the solidification of axisymmetric aluminium-alloy billets. The boundary conditions for the heat transfer include the effects of hot top, mould chill, and direct chill. The volume averaged conservation equations are solved with the explicit local meshless diffuse-approximate method. The approximation coefficients are evaluated on subdomains containing 14 nodes with the second order polynomial basis and the Gaussian weight function. Problems with instabilities due to strong convection are successfully eliminated with an adaptive shift of the weight function and evaluation position in the upstream direction. The automatic adaptive generation of computational node arrangement decreases the calculation time and in a straightforward way enables investigation of the complex flow for geometrically different inflow structures, including sharp and curved edges. The model is used for casting simulation of an Al-5.25wt%Cu alloy billet with a 120 mm radius for various inlet designs. The effect of inlet geometry on the temperature, solid fraction, melt flow, and macrosegregation is investigated. The described developments represent a first meshless numerical approach for simulation of macrosegregation of an important industrial process.