NEAR WAKE STRUCTURE OF A WALL-MOUNTED FINITE-LENGTH SQUARE CYLINDER

This paper reports an experimental investigation of the near wake of a wall-mounted finite-length square cylinder. The height-to-width ratio, Hid (H and d are the cylinder height and width, respectively), of the cylinder is 7. Experiments were conducted at a Reynolds number (Re) of 9300, based on d and the free-stream velocity (lid. The PIV measurements were performed in three orthogonal planes in the three-dimensional cylinder wake, along with flow visualization conducted simultaneously in two orthogonal planes at Re = 220. Three types of vortices, i.e. the up, base and spanwise vortices were observed and the near wake is characterized by the interactions of these vortices. Both flow visualization and two-point correlation point to an inherent connection between the three types of vortices. A model for the 3D flow structure is proposed based on the present measurements, which is distinct from previously proposed models. Other issues such as the topological characteristics, spatial arrangement and interactions among the vortical structures are also addressed.