基于PF-LBM模型的自然对流影响枝晶生长模拟

Simulation on influence of natural convection for dendrite growth based on F-LBM model

基于二元合金枝晶生长的相场模型,建立耦合流场、温度场和溶质场等物理外场的多元合金相场模型,模拟了单晶粒和多晶粒在自然对流作用下的生长,观察了枝晶凝固过程中的枝晶形貌、流场以及溶质场的变化.研究发现:温度梯度和浓度梯度改变引起自然对流,使枝晶整体的对称性遭到破坏,上游枝晶尖端生长受到促进,生长速度大于下游,水平方向枝晶尖端生长速度介于上下游之间,二次枝晶臂生长速度、浓度与一次枝晶臂基本相同,能量起伏和结构起伏使枝晶受到的影响更加明显.此外,随着各向异性强度增加,枝晶尺寸变大,生长速度加快,主枝晶臂变细,内部凹陷变明显,尖端变尖锐,二次枝晶臂间距增大.当单晶粒各向异性强度为0.05时,出现明显的“颈缩”现象,多晶粒在各向异性强度为0.03时,出现明显“颈缩”现象.

Based on the phase field model of binary alloy dendrite growth,a multifaceted alloy phase field model with the external fields such as coupling flow field,temperature field and concentration field is established.Under the natural convection,the single dendrite and multi dendrite are simulated to observe the changes of dendrite morphology,flow field and concentration field during the solidification of the dendrite.It was found that the natural convection is caused by the change of temperature gradient and concentration gradient,and the symmetry of the dendrite as a whole is broken,the upstream tip growth is promoted and its speed is larger than that of the downstream tip,and the horizontal tip growth speed locate between those of the upstream and downstream tips.The growth speed and concentration of the secondary dendrite arm are basically the same as that of primary dendrite arm,the fluctuation of energy and structure on dendrites is more obvious.In addition,with the increase of anisotropy intensity,the dendrite size becomes larger,the growth rate is accelerated,the main dendrite arm becomes thinner,the internal depression becomes obvious,the tip becomes sharp,the spacing between secondary dendrite arms increases and when the anisotropy intensity of single dendrite is 0.05,there is an obvious“necking”phenomenon,when anisotropy intensity of multi dendrite is 0.03,there is an obvious“necking”phenomenon.