Experimental investigation of the characteristics of the wake structure behind a structured porous square cylinder*

When the flow passes two-dimensional porous cylinders, the downstream wake is influenced by the mutual interaction between longitudinal and lateral bleedings. In this context, the characteristics of the wake were experimentally explored. The present porous cylinders, whose cross-sections are square (D = 24-42 mm, where D is the cylinder diameter), consist of a periodic and scalable structure based on a simple cubic lattice. By scaling the unit cell with a consistent ratio of the unit-cell length to the strut size, cylinder permeability is successfully isolated from the effect of porosity. Consequently, the structural features of the bleeding flows and their corresponding wake characteristics are systematically investigated under different levels of permeability and compared to the flow past a solid body with an equivalent diameter.

In this study, the Reynolds number based on the cylinder diameter is set to O(10^4), and the flow pattern and aerodynamic features were acquired by particle image velocimetry (PIV) and a three-component balance unit, respectively. In PIV measurements, two high-resolution PIV cameras were placed in series to maximize the streamwise field of view (FOV). Permeability, as the key control parameter, was carefully measured in an open-loop pipe flow system.