Direct numerical simulation (DNS) for gas-solid flow is implemented on a multi-scale supercomputing system, Mole-8.5, featuring massive parallel GPU-CPU hybrid computing, for which the lattice Boltzmann method (LBM) is deployed together with the immersed moving boundary (IMB) method and discrete element method (DEM). A two-dimensional suspension with about 1,166,400 75-micron solid particles distributed in an area of 11.5cm x46cm, and a three-dimensional suspension with 129,024 solid particles in a domain of 0.384cm x1.512cm x0.384cm are fully-resolved below particle scale and distinct multi-scale heterogeneity are observed. Almost 20-fold speedup is achieved on one Nvidia C2050 GPU over one core of Intel E5520 CPU in double precision, and nearly ideal scalability is maintained when using up to 672 GPUs. The simulations demonstrate that LB-IMB-DEM modeling with parallel GPU computing may suggest a promising approach for exploring the fundamental mechanisms and constitutive laws of complex gas-solid flow, which are, so far, poorly understood in both experiments and theoretical studies.
Finite volume simulations of particle-laden viscoelastic fluid flows: application to hydraulic fracture processes
精确求解复杂流体的液固两相间的耦合动量传递是水力压裂等多相输送过程中的一个基本问题。具体来说，我们需要表征的归一化平均流体颗粒力$\langle F \rangle$上的分散的固相的体积分数和复杂的流体基质的流变学的依赖性。在这里，我们使用直接数值模拟（DNS）研究蠕变流（$Re\ll 1$）的粘弹性流体通过静态随机阵列的单分散球形颗粒使用有限体积的Navier-Stokes/Cauchy动量求解器。数值研究由$N=150$不同的系统，其中归一化的平均流体-颗粒力$\langle F \rangle$作为分散固相的体积分数$ϕ$ $(0 < ϕ\leq 0.2)$和Weissenberg数$Wi$ $(0 \leq Wi \leq 4)$的函数获得。从这些预测闭合律$\langle F \rangle(Wi,ϕ)$的阻力推导出准线性Oldrophil-B粘弹性流体模型，平均而言，在$5.7\%$的DNS结果。此外，能够耦合欧拉和拉格朗日阶段的流动求解器的开发，它结合了连续相的粘弹性性质和封闭形式的阻力定律。使用该求解器模拟了两个案例研究，以评估新开发的用于处理具有代表水力压裂操作的$O(10^5-10^6)$刚性球体的含颗粒粘弹性流配置的方法的准确性和鲁棒性。
DNS of compressible multiphase flows through the Eulerian approach
Scuola Normale Superiore di Pisa（比萨高等师范学院）；Istituto Nazionale di Vulcanologia e Geofisica（意大利火山学与地球物理研究所）；Istituto Nazionale di Geofisica e Vulcanologia（意大利地球物理与火山学研究所）
