PHASE DYNAMICS OF KARMAN VORTICES IN CYLINDER WAKES

The temporal evolution of Karman vortex shedding patterns in the wake of a cylinder placed at right angles to a uniform flow is studied for Reynolds numbers (based on cylinder diameter) between 80 and 140. Focu sing on the dynamics of the vortex shedding phase in the wake planview (the plane spanned by the free-stream direction and the cylinder axis ) we study experimentally and model the response of shedding patterns to time-dependent boundary conditions imposed at the cylinder ends. By appropriate impulsive changes of end conditions, spanwise wave number ''shocks'' can be produced that travel along the cylinder span. These shock experiments, together with data from steady oblique shedding pa tterns, are used to determine the parameters for the spanwise Ginzburg -Landau model, which has already been used successfully to describe ma ny of the phenomena observed in cylinder wakes. We then demonstrate ex perimentally that, in analogy to gasdynamics, it is also possible to p roduce ''expansion waves'' of the spanwise wave number, which are well described by the Ginzburg-Landau model without further adjustment of its parameters. (C) 1996 American Institute of Physics.