Influence of external flows on crystal growth: numerical investigation

TL;DR

This study uses numerical simulations to explore how external flows influence crystal growth patterns, tip radius, and velocity, revealing flow-induced modifications to growth morphology and dynamics.

Contribution

It introduces a combined phase-field/lattice-Boltzmann simulation approach to analyze flow effects on non-facetted crystal growth, highlighting flow's impact on growth parameters and morphology transitions.

Findings

Flow modifies growth characteristics mainly through the Peclet number.

Flow shifts the dendrite-doublon transition line, favoring dendritic patterns.

Tip velocity oscillations are affected by flow and viscosity changes.

Abstract

We use a combined phase-field/lattice-Boltzmann scheme [D. Medvedev, K. Kassner, Phys. Rev. E {\bf 72}, 056703 (2005)] to simulate non-facetted crystal growth from an undercooled melt in external flows. Selected growth parameters are determined numerically. For growth patterns at moderate to high undercooling and relatively large anisotropy, the values of the tip radius and selection parameter plotted as a function of the Peclet number fall approximately on single curves. Hence, it may be argued that a parallel flow changes the selected tip radius and growth velocity solely by modifying (increasing) the Peclet number. This has interesting implications for the availability of current selection theories as predictors of growth characteristics under flow. At smaller anisotropy, a modification of the morphology diagram in the plane undercooling versus anisotropy is observed. The transition line from dendrites to doublons is shifted in favour of dendritic patterns, which become faster than doublons as the flow speed is increased, thus rendering the basin of attraction of dendritic structures larger. For small anisotropy and Prandtl number, we find oscillations of the tip velocity in the presence of flow. On increasing the fluid viscosity or decreasing the flow velocity, we observe a reduction in the amplitude of these oscillations.