SUMMARY

E'ake development behind circular cylinders at Reynolds numbersfrom 40 to 20,000 was investigatecl in a low-speed wind tunnel. Standard hot-wire techniques were used to s tudy the velocity jluctuations. The Reynolds number range of periodic vortex shedding i s divided into two distinct subranges. A t R=4O to 150, called the stable range, regular vortex streets are.formed and n o turbu-lent motion i s developed. The range R=150 to SO0 i s a transition range to a regime called the irregular range, in which turbulent velocity$uctuations accompany the periodic formation of vortices. The turbulence i s initiated by laminar-turbulent transition in the free layers which spring from the separation points o n the cylinder. Th i s transition Jirst occurs in the range R = 150 to 300. Spectrum and statistical measurements were made to study the velocity$uctuations. In the stable range the vortices decay by viscous diffusion. I n the irregular range the diffusion i s turbulent and the wake becomes fu l ly turbulent in 40 to 50 diameters downstream. I t was found that in the stable range the vortex street has a periodic spanwise structure. The dependence of shedding frequency on velocity was success-fu l ly used to measurejlow velocity. Measurements in the wake of a ring showed that a n annular vortex street i s developed