Turbulent Flow Characteristics and Modeling on Dispersed Two-Phase Flow

本文对固体颗粒在圆柱体尾流区的扩散进行了实验研究。两个圆柱体平行排列，圆柱体间的距离为S/d=0.3和2.0，圆柱体周围的气流速度为10m/S，圆柱体之间的空间中心加载了平均直径为42微米的球形草粒。Strouhal数随柱距的不同而不同，对于两相流，颗粒在较大的柱距范围内到达尾迹流区后开始分散。在此条件下，由于流场中没有涡旋相互作用，颗粒逐渐弥散。由于圆柱体之间的间隙较窄，颗粒分散较快。流场在尾流区的顶点之间存在相互作用。当顶点相互作用时，一个很大的夹带力作用在粒子上。定义为颗粒弛豫时间与大尺度旋涡特征时间尺度之比的Stokes数是颗粒扩散的主要影响因素。

An experiment study has been carried out concerning the dispersion of solid particles in a wake region of a pair of circular cylinders. Two cylinders were arranged in parallel, where the distance s between cylinders were set at s/d=0.3 and 2.0, and the air velocity around the cylinders at 10m/s. Spherical grass particles of 42mum in mean diameter were loaded at the center of the space between the cylinders.For the single-phase flow, large scale eddy was observed in the wake region by the flow visualization. Strouhal number varied with the distance between the cylinders.For the two-phase flow, the particles began to disperse after reaching the flow region of the wake over the wide distance between the cylinders. Under the condition, the particles disperse gradually because the flow field has no vortex interaction. For the narrow gap between the cylinders, the particles dispersed rapidly. The flow field has an interaction between the vertices in the wake region. A large entrainment force act on the particles while the vertices interact with each other. The Stokes number, which is defined as the ratio of particle relaxation time and characteristic time scale of the large scale vortex, is confirmed to be a dominant factor for the particle dispersion.