大型流态化多相流数值模拟的关键科学问题——曳力模型的理论分析

THE KEY SCIENTIFIC PROBLEMS IN THE EULERIAN MODELING OF LARGE-SCALE MULTI-PHASE FLOWS——DRAG MODEL

  • 摘要: 描述相间相互作用的曳力模型是决定流态化模拟成败的关键科学问题,核心是如何表征稠密非均匀流动中曳力的一般规律. 首先综述了现有曳力模型的发展现状和优缺点,然后讨论了流态化系统能量分析方法(energy minimization multiscale method, EMMS),以及在此基础上建立的曳力模型及其发展历程,重点分析了EMMS 理论在代表非均匀流动特征的颗粒团尺寸、内部固含率等关键参数上的缺陷、文中的修正方法和实验检验结果. 最后,讨论了曳力模型的发展方向即普适性问题.

     

    Abstract: A Eulerian two-fluid model based on the kinetic theory of granular flow is important for the calculation of large-scale multi-phase flows and reactions. The drag model which describes the interphase interactions is critical with respect to the calculation accuracy. This paper reviews various methods to develop drag models for dense heterogeneous gas-solid flows and discusses their merits and demerits. Based on the energy analysis of multi-phase flows, an energy minimization multi-scale (EMMS) drag model is established. The core of the EMMS model is the conservation equations of mechanical energy and the solution of such equations with the stability condition that the energy for the particle suspension and transport reaches the minimum. This paper discusses the development process of the EMMS model and points out its substantial defects in describing cluster characteristics. New descriptions of cluster characteristics are proposed and verified with experimental data. The predicted drag with the new cluster descriptions agrees well with experimental results, indicating the effectiveness of the model revision. Finally, this paper discusses the EMMS model defects in universal applications and suggests the developing directions.

     

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