基于稳定性约束的高效多相流连续-离散耦合模拟

The problem of bad accuracy and slow computaion speed is critical on the simulation of gas-solid flow in industrial reactor with complicated structures, which may be figured out by efficiently integrated multiscale models dealing with multiscale problems. The coupling method of Computional Fluid Dynamics and coarse grained Discrete Element Method is adopted in this proposal, which tracks every particle to describe particles' movement in complex gas-solid two phase flow, and is more accurate than the frequently-used two-fluid model.This proposal is to solve the problem of calculation scale based on CFD-DEM by a series of methods: establishing coupling method with high precision in unstructured mesh; initiating the fluid field by macroscale EMMS model to accelerating the simulation to achieve stochastic steady state; accelerating simulation by large-scale parallel calculation technique; adaptive time step restrained by global stability criterion. The coupling of these methods creats a gas-solid simulation mode with high-efficiency and accuracy,and contributes to explore the complex process in reactor, improve predictive ability, and theoretically guide the optimal design and scale-up of industrial device.

对结构复杂的工业气固反应器的模拟中，精度差、速度慢的问题十分突出。利用多尺度模型高效集成处理反应器中的多尺度问题，可望解决该不足。本申请将采用连续介质模型与粗粒化的离散模拟相结合的多尺度方法，建立非结构网格中CFD-DEM耦合算法，直接追踪每个颗粒的运动轨迹，描述气固复杂运动中颗粒的运动情况，达到较传统的双流体模型更高的模拟精度；采用EMMS模型优化初场分布并约束其演化过程，以缩减需要模拟的物理时间、增大时间步长；利用研究小组已有基础的粗粒化固相离散模型及其GPU并行计算方法减少计算量、提高计算效率；建立本方法与成熟商业及开源软件的耦合模式以处理复杂构体。以上四者紧密结合，形成高效、高精度的工业气固流动模拟方法，为反应器优化设计和放大提供支持。

在结构复杂的工业气固反应器的模拟中，精度差、速度慢的问题十分突出。利用多尺度模型高效集成处理反应器中的多尺度问题，可望解决该不足。本项目建立了连续介质模型与粗粒化的离散模拟相结合的多尺度方法，达到了较传统的双流体模型更高的模拟精度，建立了非规则网格中的流体-颗粒耦合方法，实现了以全局EMMS模型预测的流场分布来约束计算初始状态，加速了计算达到统计稳态的时间。并利用基于GPU的大规模并行CFD-DEM粗粒化计算方法，完成了两个工业反应器连续-离散耦合模拟计算，分析了其中的微观宏观流动规律，对工业器的优化设计提供了理论依据和改进方案。