探讨复杂结构反应器内气液两相数值模拟的网格拓扑方法

网格拓扑方法直接影响到复杂结构的反应器内,气液两相数值模拟的收敛速度和计算精度。本文在引入中心下料管和环管式气体分布器的环流反应器内,通过实验,考察了不同表观气速下轴、径向局部气含率和气泡上升速度的分布特性。在此基础上,使用商业软件ANSYS CFX10．0,采用非结构化和杂交两种不同的网格拓扑方法,为该反应器作数值模拟。从定性角度来看,两者结果均表明内、外环气含率均随表观气速的增大而增大;外环循环流入内环的气泡量少;在同一表观气速下,外环气含率远远低于内环;内环气泡速度远远大于外环,这些规律与实验数据基本吻合。从定量角度来看,杂交网格法可清楚地反映出气体分布器和下料管液体入口的影响,以及外环气泡速度方向在导流筒外壁处向上,而这些却是非结构化网格法难以实现的。这说明了在该反应器内的气液两相数值模拟中,采用杂交网格法比单纯的非结构化网格法准确得多。因此,对于复杂几何结构的反应器,本文建议采用杂交网格法。

Probing mesh topology for gas-liquid system in complex reactors

Mesh topology has a great effect on both calculation precision and convergence speed during the numerical simulation.The radial and axial distributions of gas holdups and the velocities of bubbles in a loop reactor with a down tube and an annulus gas distribu- tor are investigated experimentally under different superficial gas velocities in this paper.Two different kinds of meshed methods,i.e. unstructured mesh and hybrid mesh,are employed for simulating the hydrodynamic characteristics in the platform of ANSYS CFX10.0 software package.In the view of quality,the simulated results obtained by these two mesh methods are in fair agreement with experi- mental data,which includes that either gas holdup or bubble velocity increases with increasing the superficial gas velocity in the whole reactor,the bubbles enter the draft tube from the annular can be neglected in the ranges of our operating conditions,and the gas holdup and the bubble velocity in the external loop is much lower than those in the inner loop.In the view of quantity,the results by the hybrid mesh method can show obviously the influence of the gas distributor and the down tube on the hydrodynamics in the local regions and the direction of bubble velocity near the draft tube outer wall,however,which can not achieved by the unstructured mesh method.Thus it can be found that the hybrid mesh method results are better agreement with experiment data than the unstructured mesh method re- suits in simulating the hydrodynamic characteristics of this reactor.Therefore,the hybrid mesh technique is an effective method for simulating the gas-liquid reactor with complicated geometrical configuration in the paper.