Effects of rotation on a nonaxisymmetric chimney convection during alloy solidification

Abstract

Nonlinear buoyancy-driven convection in the melt and in cylindrical chimneys within a mushy layer during alloy solidification is investigated under a high-gravity environment, where the rotation axis is inclined at an angle γ to the high-gravity vector. In the final form of the solidified material these chimneys produce freckles, which are imperfections that reduce the quality of the solidified material. Asymptotic and scaling analyses are applied to a nonaxisymmetric convection in the finite Prandtl number ( P r ) melt and in the chimneys. It is found that there are P r - and rotation-dependent ranges where the wall of chimneys may or may not be vertical. There are also γ-, P r - and rotation-dependent ranges, where convection in the chimneys can increase or decrease with increasing rotation rate. The results are generally in agreement with available experimental observations.