Turbulent Flow Characteristics and Modeling on Dispersed Two-Phase Flow

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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.