A Numerical Benchmark Exercise on Thermal and Thermosolutal Natural Convection in Liquid Alloys

During casting of alloys, chemical inhomogeneities (macrosegregations) result from solute transport by the flow in the mushy solidification zone. This flow is coupled with the thermosolutal natural convection in the fully liquid zone. Vigorous natural convection occurs either in the initial stage of casting, until the superheat is extracted; or throughout, in processes where thermal gradients are maintained (DC casting, remelting processes). Because of inherent strong nonlinearities, due to the low Prandtl (~10(-2)) and high Lewis numbers (~10(4)) of liquid metals, these flows are notoriously difficult to simulate. In the framework of the French project SMACS we present a numerical benchmark exercise comparing the performance of four numerical codes in the prediction of laminar thermal and thermosolutal natural convection related to small castings. We compare predictions on prototypal cases of convection in a square cavity and present the sensitivities of the predictions of global and local heat and mass transfer.