枝晶生长和气泡形成的数值模拟

摘要

本文建立了二维的格子玻尔兹曼方法-元胞自动机（lattice Boltzmann method-cellular automaton,LBM-CA）耦合模型,对凝固过程中枝晶生长和气泡形成进行模拟研究.本模型采用CA方法模拟枝晶的生长,根据界面溶质平衡法计算枝晶生长的驱动力.采用基于Shan-Chen多相流的LBM模拟气泡在液相中的生长和运动.在LBM-CA的耦合模型中包含了固-液-气三相之间的相互作用.应用Laplace定理和模拟气-液-固三相之间的润湿现象对模型进行了验证.应用所建立的LBM-CA耦合模型模拟研究了气-液相互作用系数对单气泡生长的影响.发现单气泡的生长速度和平衡半径随气-液相互作用系数的增大而增大.定向凝固过程中枝晶和气泡生长的模拟结果再现了枝晶的择优生长、气泡的优先形核位置、气泡的长大、合并、在枝晶间受挤变形以及在液相通道中的运动等物理现象,与实验结果符合良好.此外,初始气体含量越高,凝固结束时气泡的体积分数也相对较高.本模型的模拟结果可以揭示在凝固过程中气泡形核、生长和运动演化以及与枝晶生长相互作用的物理机理.%A two-dimensional（2D） lattice Boltzmann method（LBM）-cellular automaton（CA） coupled model is developed for the simulation of dendritic growth and bubble formation during solidification.In the model,the dendritic growth is simulated by a CA approach.The driving force of dendritic growth is determined by a local solute equilibrium approach.The LBM based on the Shan-Chen multiphase flow scheme is adopted to simulate the growth and the motion of bubbles in liquid.The interaction mechanism between dendrites and bubbles is embedded in the model.Model validation is carried out by comparing the simulations with the Laplace law,and by simulating the wettability of a bubble on a smooth solid surface.The proposed model is used to study the effect of gas-liquid interaction coefficient on single bubble growth.It is found that the growth velocity and the equilibrium radius of bubble increase with the gasliquid interaction coefficient.The simulations of the dendritic growth and bubble formation during directional solidification reproduce the physical phenomena,including dendritic competitive growth,the preferential nucleation locations of bubbles,and bubble growth, coalescence,deformation due to the squeeze of neighboring dendrites,as well as bubble motion in the liquid channels.The simulation results are compared reasonably well with the experimental results.In addition,gas pore volume fraction increases with the initial gas content.The simulations of the present LBM-CA model provide an insight into the physical mechanism of bubble nucleation,growth, and motion,as well as the interaction between the dendritic growth and bubble formation during solidification.