气固鼓泡床的全尺度直接数值模拟

Fully-Resolved DNS of a Gas-solid Bubbling Bed

颗粒全尺度直接数值模拟由于不引入任何相间作用力封闭模型、同时又考虑了颗粒相与流体相之间的四向耦合,因而具有极高的计算精度和准度。本文采用内嵌边界多重直接力算法结合软球碰撞模型对实验室尺度的气固鼓泡流化床装置进行了全尺度直接数值模拟。计算结果真实还原了鼓泡流态化的流动情形,且能有效地捕捉装置内部流场的详细运动情况和涡结构。对流化床内颗粒在传统的离散元模型框架下进行曳力统计发现,平均曳力比全尺度模拟结果小约20%~30%。其具体数值因选取比较的曳力模型和统计网格而异。改进传统曳力模型需考虑颗粒群的非均匀性以及颗粒拟温度。

Particle fully-resolved DNSs are of high precision and high fidelity,as no closed models for interphase interactions and four-way coupling between particle phase and fluid phase are considered in these simulations.Fully-resolved DNS of a laboratory-scale gas-solid bubbling bed was carried out using the multi-direct forcing scheme and immersed boundary method combined with soft-sphere collision model.Calculation results restore the flow pattern of bubbling fluidization and efficiently capture the detailed motions and the vortex structures in the nuidized bed inside.Particle drag statistic under the framework of DEM shows that the DEM-type average drag force is about 20~30%smaller than the DNS-type value.Exact values depend on the drag model and the statistical grid under test.A modification of the traditional drag models should take the heterogeneity of the particle group and the effect of the granular temperature into consideration.