Instabilities in the wake of a circular disk.

Flow past a disk was investigated experimentally in a low-velocity water channel in the range of intermediate Reynolds numbers. Systematic experiments with flow visualization and particle image velocimetry measurements are presented. Different disks with the aspect ratio χ = d/h varying from 1 to 24 were investigated. The measurements were made in the range of Reynolds numbers from 0 to 500, where stationary and oscillatory instabilities appear. The influence of the aspect ratio on the value of onset instability, the evolution of perturbation, and the obtained vorticity bifurcation branches of the instability were identified.