Note on Transition to Turbulence in Vortex-Street Wakes

In their pioneering paper published in 1917 Nayler and Frazer showed that the process of vortex formation behind a circular cylinder can have significant three-dimensional features even when care is taken to create two-dimensional flow. Hama produced photographs which show initially straight vortex filaments becoming curved some distance behind the cylinder, with consequent three-dimensional flow. In their experiments on boundary layers Hama et al found the formation and development of “vortex loops” from such curved vortex filaments to be an essential feature preceding transition from laminar to turbulent flow, and they stated that the same would be true for transition in wakes and jets.