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首页> 外文期刊>Applied Mathematical Modelling >The discrete nature of grain attachment models in simulations of equiaxed solidification
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The discrete nature of grain attachment models in simulations of equiaxed solidification

机译：等轴凝固模拟中晶粒附着模型的离散性

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摘要

Grain refiner is often added to aluminum and magnesium alloys during solidification processing to encourage the development of a fine equiaxed grain structure. Numerical modeling of such processes face the challenge of considering the effect of free floating grains that nucleate on grain refiner particles, are advected in the bulk fluid flow, and eventually coalesce to form a permeable, rigid solid structure. While several models have been developed to consider the advection of solid grains, the attachment of these grains is uniformly treated on a discrete, cell-by-cell basis. In a previous study, channel segregates were observed in the predicted composition field of equiaxed solidification simulations and were found to exhibit an extreme grid dependence. These channels were examined in the present study in detail for two different grain attachment models, one that assumed coalescence occurs at a constant and uniform volume fraction solid, and one that considered the effects of the local solid velocity field. The mechanism of the initiation and propagation of these channels was explored, and their physical relevance considered. It was concluded that these defects were primarily numerical artifacts arising from the discrete nature of the grain attachment models, and therefore, necessarily occurred on the length scale of the grid spacing. Development of an alternative attachment model that avoid this numerical problem is the subject of ongoing research.
机译：晶粒细化剂通常在凝固过程中添加到铝和镁合金中，以鼓励形成细等轴晶粒结构。这种过程的数值建模面临着挑战，即要考虑成核的自由漂浮颗粒对晶粒细化剂颗粒的影响，这些自由漂浮颗粒会平流到整体流体流中，最终聚结形成可渗透的刚性固体结构。尽管已经开发了几种模型来考虑固体颗粒的对流，但是这些颗粒的附着在离散的，逐个单元的基础上进行了均匀处理。在先前的研究中，在等轴凝固模拟的预测组成区域中观察到通道偏析，并发现它们表现出极端的网格依赖性。在本研究中，针对两个不同的晶粒附着模型对这些通道进行了详细检查，其中一个假定合并发生在恒定且均匀的体积分数固体中，另一个则考虑了局部固体速度场的影响。探索了这些通道的启动和传播的机制，并考虑了它们的物理相关性。可以得出结论，这些缺陷主要是由于晶粒附着模型的离散性而产生的数值伪影，因此，这些缺陷必定发生在网格间距的长度尺度上。避免这种数值问题的替代附件模型的开发是正在进行的研究的主题。

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