基于LBM-CA模型的自然对流下液氢中固空枝晶生长模拟

Numerical simulation of air solidification in liquid hydrogen under natural convection with LBM-CA model

固空沉积是液氢系统的安全隐患之一,为探究自然对流作用下固空颗粒在液氢系统中的形成过程,建立LBM-CA(格子玻尔兹曼—元胞自动机方法)耦合模型模拟空气(氮氧混合物)在液氢中的凝固过程。模拟探究了自然对流作用对固空晶体生长的影响,模拟结果表明:自然对流使固空枝晶不再表现为纯扩散条件下的对称生长,迎流侧枝晶生长受到促进,下游由于溶质聚集枝晶生长受到抑制。多晶粒在自然对流条件下生长时,中心晶粒受周围晶粒的影响,生长受到明显抑制。自然对流使溶质分布均匀化,加快凝固速率,减小凝固过程中的峰值浓度,有利于降低液氢系统的安全风险。

Solid-air deposition is one of the hidden dangers of liquid hydrogen system.In order to explore the formation process of solid-air particles in liquid hydrogen system under natural convection,the coupled model of Lattice Boltzmann Method(LBM)and Cellular Automation(CA)has been proposed to simulate the solidification process of air(nitrogen and oxygen mixture)in liquid hydrogen.The simulation explored the influence of natural convection on the growth of solid-space crystals.The simulation results show that natural convection makes solidspace dendrites no longer exhibit symmetrical growth under pure diffusion condition.The growth of the upstream side dendrites is promoted,and the downstream dendrites are inhibited due to solute aggregation.When polycrystalline grains grow under natural convection conditions,the central grain is affected by the surrounding grains,and the growth is obviously inhibited.Natural convec tion makes the solute distribution uniform and results the solidification rate is increased.In addi-tion,the convection reduces the peak concentration during the solidification process,and there-fore reduce the safety risk of the liquid hydrogen system.