On the spatio-temporal structure of cylinder wakes

The wake of a short aspect ratio cylinder placed in a uniform flow is exper imentally investigated. After having characterized the temporal behavior of the Benard-Von Karman vortex shedding by the use of a classical hot-wire a nemometer, an ultrasound anemometry technique is applied to study the spati al critical behavior of the envelope of the transverse velocity of the wake . It is shown that this envelope which represents the spatial form of the g lobal mode of the wake, follows universal scaling laws which are in agreeme nt with a second order phase transition. In a second set of experiments, th e behavior of the longitudinal velocity fluctuations is also investigated. It is discovered that there is a special point several diameters behind the cylinder, which plays a role of a wave maker. Finally, for very small aspe ct ratio cylinders, symmetric vortex shedding is reported and interpreted u sing a system of coupled oscillators.