Abstract: Fine grid resolution is necessary to fully demonstrate the accuracy of two-fluid model(TFM) in predicting gas-solids flows in the riser section of circulating beds.Insufficient grid resolutions will likely lead to incorrect solutions.In most industrial applications involving large devices,it is impractical to use fine grids,and therefore,constitutive models that are suitable for the coarse-grid TFM simulations are required.It has been reported in some literatures that microscopic drag laws,such as those due to Gibilaro and Gidaspow,did not yield grid-independent solutions over the range of grid sizes investigated in some test problems.Filtered two-fluid models were developed using the results of highly resolved simulations.A filtering procedure was applied to the results of these simulations to deduce the constitutive models for the residual correlations appearing in the corresponding filtered TFM equations.These equations were appropriate for coarse-grid simulations of gas-particle flows.Using the same example studied by Mckeen and Pugsley(2003),it was first demonstrated that grid-independent predictions could be afforded by a filtered TFM,in which filtered drag and particle phase stress models were included.Then grid-independent and experimentally consistent solutions could also be obtained with filtered TFM model when filtered particle phase stress model was replaced with kinetic theory model as long as filtered fluid-particle drag force model was used.

Key words: sub-grid, filtered two-fluid model, grid-independence, coarse grid

摘要： 基于双流体方程和颗粒动力学理论的计算模型被广泛应用于流化床的气固两相流数值计算,高精度网格是其准确计算流动的必要条件。一些经典的微尺度阻力模型,其网格尺度决定其模拟结果的精度。亚格子过滤双流体模型是一种有效的适用于粗糙网格的计算模型,其包含的气固相间作用力和颗粒相应力本构方程是在高精度网格条件下,以微尺度双流体方程和颗粒动力学理论计算得到的气固流场为基础,对计算结果进行小尺度过滤后得出。使用亚格子过滤双流体模型替换基于颗粒动力学理论的双流体模型,针对同一物理问题,在不同网格尺度下进行了数值计算,结果表明此计算模型相比经典阻力模型具有较好的网格无关特性,并且和实验结果较为一致。同时也对颗粒动力学理论与之相结合进行了尝试,即仅使用亚格子过滤阻力模型,颗粒相应力仍然使用颗粒动力学模型,其计算结果的网格无关性及与实验值的吻合程度优于经典模型。

关键词: 亚格子, 过滤气固双流体模型, 网格无关性, 粗网格