Investigation of the role of porosity on the flow past a sphere

The flow past a sphere is a classical fluid dynamics problem, but many aspects of it remain unknown, especially in turbulence. Inspired by the dandelion seed head, a porous structure found in nature, we are particularly interested in the role of porosity on the flow structure past a sphere in turbulent flows. To study this, we constructed hollow spheres with varying porosity and measured the wake field using 2D Particle Image Velocimetry in a water tunnel at Reynolds number ~10,000-20,000. The resulting flow field was analyzed for the effect of porosity on the flow separation location, the wake size behind the sphere, and the downstream location of the recirculation zone. The results of this work have implications for fluid-structure interactions between often porous biological entities and wind.