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A combination of the phase-field approach and the lattice-Boltzmann method is used to simulate non-facetted crystal growth from a supercooled melt in external flows.
Different regions of the morphology diagram for two-dimensional systems are explored. Selected growth parameters are determined numerically. Depending on the level of anisotropy and supercooling, dendrites or doublons are obtained. Both the influence of shear flow and parallel flow on these two basic morphologies are investigated. It is shown that for sufficiently large flow velocities, an oncoming flow can lead to tip oscillations of the dendrite and, consequently, to the generation of coherent side branches. For growth patterns at moderate to high supercooling and relatively large anisotropy, the values of the tip radius and selection parameter are computed as a function of the growth Péclet number, the result giving rise to interesting implications concerning the availability of current selection theories as predictors of growth characteristics under flow. Moreover, a modification of the morphology diagram in the plane supercooling 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. |
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