In nature, bluff bodies immersed in flows often have a rough surface morphology. An example is an ovulate pine cone whose roughness is characterized by scales arranged according to Fibonacci spirals, possibly creating flow patterns that favor pollination. An idealized model of a 3D axi-symmetric bluff body is a smooth sphere who’s wake characteristics (e.g. vortex shedding frequency, critical Reynolds number) have been studied in detail. In this study, we have used time resolved, high-speed (50-3000 Hz) Particle Image Velocimetry (LaVision GmbH) to study the wake of several smooth and rough spheres (diameters, D 8,10,12 mm), rigidly mounted in a closed-loop water channel. The rough spheres with different roughness depth and width, were designed and generated by 3D printing technique. Measurements were taken in a horizontal laser sheet plane positioned at the sphere’s center at Reynolds numbers not exceeding 5000. Data processing is currently ongoing and results are expected to provide answers on the effect of this specific roughness on the characteristics of the flow in the wake of a stationary sphere. Points of interest are the Strouhal/Reynolds number dependence, separation point dynamics and vortex shedding dynamics. The latter are characterized by hairpin shaped vortices and the present measurements map their life cycle.
