气固流态化模拟中流体解析的DPM方法研究

This proposal aims at improving the accuracy of gas-solid fluidization simulations with discrete particle method (DPM) by applying mesoscience methodology. Mesoscale structures in fluidizations lead to the heterogeneous gas and solid distributions inside computational grid. Coarse grained DPM, e.g. MP-PIC, which is adopted as the gas-solid simulation frame in this proposal, is capable of simulating industrial scale fluidization applications. And it can resolve the sub-grid scale particle movement, while the fluid movement can only be resolved to grid scale, which leads to the low simulation accuracy. Thus, to resolve the sub-grid scale flow field is an urgent problem for improving the simulation accuracy. Up to now, there is seldom report on resolving sub-grid flow field for DPM. However, EMMS theory has been successfully applied to resolve sub-grid gas-solid two-phase structures for two-fluid method. To this end, the current proposal plans to develop a sub-grid flow field resolving method based on detailed particle distribution by incorporating EMMS theory into MP-PIC. And a heterogeneous drag force model accounting for different mesoscale structure characteristics will be constructed subsequently based on the resolved sub-grid flow field. Further, the relationship between the particle scale and the grid scale heterogeneous drag force will be investigated to clarify that if the grid scale heterogeneous drag force constitutive equation can be directly applied in DPM. This research work can help to improve the simulation accuracy of gas-solid fluidization simulation with DPM method and it is also of great importance in gas-solid fluidization research and industrial application.

本项目致力于解决离散粒子方法（DPM）在模拟气固流态化时计算精度不高的问题。流态化中介尺度结构的存在导致计算网格内部气固两相非均匀分布。粗粒化后的DPM，如MP-PIC（本研究采用的DPM算法框架）能胜任气固流态化工业应用的模拟，且能解析亚网格尺度的固相运动，但对流体的计算仅能解析到网格尺度，导致计算精度较低。亚网格流动的解析是亟待解决的问题。对此，DPM领域还少有研究涉及，但在双流体领域，EMMS理论已成功用于解析亚网格气固两相结构。鉴于此，本项目在MP-PIC中引入EMMS原理，发展基于详细粒子分布的流动解析算法，构建基于介尺度结构的非均匀曳力模型，考虑不同介尺度特征结构对亚网格流动解析的影响。在此基础上研究颗粒和网格尺度非均匀曳力间的关系，明确能否直接在DPM中使用网格尺度的非均匀曳力本构关系。本研究将有助于提高DPM模拟气固流态化的精度，对气固流态化的研究和工业应用都具有重要意义。

本项目致力于解决离散粒子方法（DPM）在模拟气固流态化时计算精度不高的问题。流态化中介尺度结构的存在导致计算网格内部气固两相非均匀分布。粗粒化后的DPM，如多相流质点网格法（MP-PIC，本研究采用的DPM算法框架）能胜任气固流态化工业应用的模拟，且能解析亚网格尺度的固相运动，但对流体的计算仅能解析到网格尺度，导致计算精度较低。亚网格流动的解析是亟待解决的问题。对此，DPM领域还少有研究涉及，但在双流体领域，能量最小多尺度（EMMS）理论已成功用于解析亚网格气固两相结构。鉴于此，本项目在MP-PIC中引入EMMS原理，发展了基于详细粒子分布的流动解析算法，构建了基于介尺度结构的非均匀曳力模型，考虑了不同介尺度特征结构对亚网格流动解析的影响。在此基础上研究颗粒和网格尺度非均匀曳力间的关系，发现在颗粒尺度非均匀曳力修正系数随滑移速度增大而降低，而在网格尺度非均匀曳力修正系数随滑移速度增大而增大。进一步又建立了能考虑介尺度结构效应的非均匀固相应力模型。本研究将有助于提高DPM模拟气固流态化的精度，对气固流态化的研究和工业应用都具有重要意义。