Coherent vortex structures in the wake of a rigid and an externally driven disk

Coherent vortex structures were studied by comparing the large scale coherent flow structure in the wake of a rigid vertical circular disk with the turbulent structures behind the externally driven disk. The periodic vortex structures in these wakes can be decomposed via cross-correlation measurements with hot wires and microphones, particularly by using representations of coherences, phase relations, and azimuthal modes. In the very near wake, coherent periodic pressure oscillations due to pulsing of the recirculation bubble are superposed onto pressure fluctuations of the naturally occurring helical vortex structures which dominates in the entire flow region outside the recirculation bubble.