Wake transition of a rolling sphere

We present dye visualizations of the flow generated by a sphere rolling along a solid surface in a quiescent fluid at low Reynolds numbers. Recent experimental and numerical studies of this configuration (Stewart et al. 2008, 2010) have shown a transition from steady to periodic flow at a Reynolds number Re (based on the sphere diameter and rolling speed) near 100. The unsteady flow involves the shedding of hairpin vortices, and the flow remained symmetric in the Reynolds number range considered, up to Re = 200. The present visualizations show that for higher Re the spatial symmetry of the unsteady wake is lost.