基于关键亚网格量的气固两相流介尺度非均匀曳力模型研究

Gas-solid flows are ubiquitous in the field of energy and chemical industry, which is the focus of national development. The meso-scale heterogeneous structures due to the gas-particle interaction are considered as the key factors affecting these complicate flows. Although the filtered two fluid model (fTFM), which is widely used in the simulations of gas-solid flows at reactor scale, could consider the influence of meso-scale heterogeneous structure at a certain extent. However, fTFM still exists deficiencies as follows: 1. Lack of theoretical analysis of the constitutive relation; 2. The selections of the conditional average indices are still too simple during the modeling. These deficiencies lead to the inaccurate drag predication in current fTFM and ambiguous mechanism of meso-scale heterogeneous structures. This project, based on the direct theoretical derivation of the meso-scale heterogeneous drag, combining with comprehensive analysis of filtered data, aim to find the most important sub-grid quantities which affecting the heterogeneous drag. Furthermore, this project would interpret the mechanism of the meso-scale heterogeneous structures’ influence on the gas-solid drag force and provide theoretical basis for the research on the meso-scale heterogeneous drag. Additionally, the sub-grid quantities would be modeled using extended conditional average indices, combining the modeling schemes used in large eddy simulations (LES) with the transfer laws of the inhomogeneity of momentum structure with different filtered scales. Finally, an accurate heterogeneous meso-scale drag model for the gas-solid two-phase flows based on the key sub-grid quantities would be established for industrial-scale simulations.

气固两相流是国家重点发展的能源化工领域内的常见流动，而气体与颗粒相互作用形成的介尺度非均匀结构被认为是影响整体流动的关键因素。虽然目前应用于反应器尺度的过滤双流体方法（fTFM）可以在一定程度上考虑介尺度非均匀结构对整体流动的影响，但是仍然存在本构关系理论分析不足，构建模型过程中条件平均指标选择简单的问题，从而导致了目前的介尺度非均匀曳力模型准确度不高且无法解释介尺度非均匀结构对曳力的复杂影响机理。本项目将基于对介尺度非均匀曳力的直接理论推导，结合全面的过滤数据分析，找到影响非均匀曳力的关键亚网格量，揭示介尺度非均匀结构对气固相间曳力的影响机理，为介尺度非均匀曳力的研究提供理论支撑。进而借鉴大涡模拟（LES）中亚网格量的建模思想，结合数据分析得到不同尺度上的动量结构不均匀性的迁移传递规律，扩展条件平均指标，构建亚网格模型，最终建立可用于工业尺度的准确气固两相流介尺度非均匀曳力模型。

气固两相流是国家重点发展的能源化工领域内常见流动，而气体与颗粒相互作用形成的介尺度非均匀结构被认为是影响整体流动的关键因素。目前已有的介尺度非均匀曳力模型存在本构关系理论分析不足导致的建模准确度不高、影响机理不明确等问题。本项目一方面对作为介观曳力构建基础的微观曳力模型进行了重要修正。本项目基于可解析到颗粒表面的直接数值模拟方法对包含不同浓稀相界面的颗粒团聚结构在不同雷诺数下进行数值分析和理论推导,揭示了浓稀相界面存在对气固相间曳力的影响机理，构建了可以准确捕捉浓稀相界面附近气固相间曳力的微观曳力模型。另一方面基于准确的微观曳力模型开展了大规模的细网格双流体方法计算，通过数据统计分析和介尺度非均匀曳力的直接理论推导，找到影响非均匀曳力的关键亚格子量，揭示介尺度非均匀结构对气固相间曳力的影响机理。进而借鉴大涡模拟（LES）中亚格子量建模思想和机器学习的数据相关性分析建模理论，最终构建了应用范围广、尺度无关性高、预测能力强的气固两相流介尺度非均匀曳力模型。后验计算显示其结果相较于其它模型更加接近于实验结果或细网格模拟结果。