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On the numerical prediction of channel segregation

机译：关于通道隔离的数值预测

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The prediction of freckles in a numerical model of alloy solidification was critically evaluated through a series of simulations of the cylindrical static casting of aluminum alloy 7050. Artificial numerical constrains in the number of iterations per time step were used to exaggerate the formation of freckles for ease in understanding the mechanism behind channel initiation and propagation. It was found that initial protrusions at the solidification front caused by instabilities in the solution to the highly non-linear governing equations cause a feedback loop in the solid fraction, momentum, and composition fields that allows channels to initiate and propagate. Unfortunately, the initial instabilities in models of this type are limited to the length scale of the numerical grid rather than the dendrite arm spacing which produces such variation in their physical counterparts. For macroscale simulations where excessive grid refinement is not computationally viable, it is recommended that freckle formation be suppressed by the application of an appropriate convergence criterion and the minimization of numerical noise originating from convergence residuals.
机译：通过一系列对7050铝合金圆柱型静态铸造的模拟，对合金凝固数值模型中的雀斑预测进行了严格评估。为方便起见，使用了每时步迭代次数的人工数值约束来夸大雀斑的形成。了解信道启动和传播的机制。已经发现，由高度非线性控制方程的解中的不稳定性引起的凝固前沿的初始突出会在固体分数，动量和成分场中引起反馈回路，从而允许通道启动和传播。不幸的是，这种类型的模型中的初始不稳定性仅限于数字网格的长度尺度，而不是枝状枝晶间距，枝状枝距在其物理对应物中产生这种变化。对于在网格上无法进行过度细化的宏观模拟，建议通过应用适当的收敛准则并最小化源自收敛残差的数值噪声来抑制雀斑形成。

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