CFD-DEM模型最优网格尺寸的理论推证

Theoretical validation on the optimal mesh size of CFD-DEM model

在多相流数值模拟中,合理确定流体网格尺寸对未解析CFD-DEM模型计算精度至关重要。针对网格尺寸问题,以单颗粒沉降运动为例,结合CFD-DEM数值模型,对最优网格尺寸开展了理论推证研究。研究表明,网格尺寸变化通过孔隙率参数影响颗粒拖曳力的分配,进而影响数值模拟的结果。基于此,提出了多相流中考虑孔隙率影响的阻力系数推导方法,并以Gidaspow模式为例,对比分析了不同孔隙率条件下单颗粒沉降的理论、试验与数值结果,验证了理论推导方法的合理性。结果表明,处于滞性状态下的颗粒受网格尺寸影响较大,建议网格尺寸大于颗粒尺寸的5倍;处于过渡状态和紊动状态下的颗粒影响较小,建议网格大于粒径3倍。研究结果可为多相流在流固耦合参数设置提供理论支撑。

In the numerical simulation of multiphase flow,it is very important to determine the mesh size of the fluid model reasonably for the computational accuracy of the unresolved CFD-DEM model.Taking the settling motion of single particle as an example,this study focuses on the optimum mesh size of the CFD-DEM model fluid model with the theoretical support.The results show that the changes of mesh size affect the distribution of the particle drag force through the porosity,and then influence the numerical simulation results.Based on this,a method was proposed to calculate the drag coefficient in multiphase flow considering the influence of porosity.Furthermore,the theoretical,experimental and numerical results of single particle settling with different porosity were compared and analyzed based on Gidaspow formula,which verified the rationality of the theoretical derivation method.The results show that the particles in the viscous state are greatly affected by the mesh size,and it is suggested that the mesh size is larger than 5 times the particle size.Particles in the transition and turbulent state are less sensitive to the mesh size,and it is suggested that the mesh size is larger than 3 times the particle size.The research results can provide theoretical support for the parameter setting of multiphase flow in fluid-solid coupling.