The paper presents a numerical investigation on the junction flow occurring at the intersection between a wall and a protruding circular cylinder. Simulations of flow for Reynolds number (Re) in the range [125 - 20000] have been carried out using OpenFOAM, an open source CFD tool. Plots of stream tracers have been used to qualitatively characterize the flow topology as either attachment or separation based on the type of singular points, classified as nodes and saddle points. Quantitative variations of momentum flux have been applied to identify a key mechanism for the transition of topology using the relative momentum strength of the incoming and reverse flow. Effect of a thinner boundary layer has been assessed by (i) imposing a reduced wall shear stress, and (ii) increasing the Reynolds number. Features of a typical unsteady flow, in the transition regime, at Re = 20000 have been predicted using Large Eddy Simulation (LES) with a one-equation eddy viscosity sub-grid scale model. Description of the time evolution of the topology at Re = 20000 has been able to validate the one-equation model in OpenFoam as well as to further validate the key mechanism identified for topology transition.

本文对壁与突出圆柱体相交处发生的结流进行了数值研究。雷诺数的流动模拟 ( Re) 范围 [125 - 20000] 已使用 OpenFOAM（一种开源 CFD 工具）进行。流示踪图已被用于根据奇异点的类型将流动拓扑定性地表征为附着或分离，分类为节点和鞍点。动量通量的定量变化已被应用于使用流入和反向流动的相对动量强度来确定拓扑转换的关键机制。已通过 (i) 施加减小的壁剪切应力和 (ii) 增加雷诺数来评估较薄边界层的影响。典型非定常流动的特征，在过渡区，在Re = 20000 已经使用大涡模拟 (LES) 和一个方程涡粘度子网格比例模型进行了预测。Re  = 20000 时拓扑的时间演化描述已经能够验证 OpenFoam 中的单方程模型，并进一步验证为拓扑转换确定的关键机制。