It is now well-known that the wake transition regime for a circular cylinder involves two
modes of small-scale three-dimensional instability, modes “A” and “B”, occurring in different
Reynolds number ranges. These modes are quite distinct in spanwise lengthscale and in
symmetry, and they are found to scale on different physical features of the flow. Mode A has
a large spanwise wavelength of around 3–4 cylinder diameters, and scales on the larger
physical structure in the flow, namely the core of the primary Kármán vortices. The feedback …