Spanwise modulation of a three-dimensional wake using distributed forcing

Synthetic jets that are spatially distributed in the spanwise direction are used to control the flow over a circular cylinder. The Reynolds number based on the cylinder diameter and the free-stream velocity is Re = 500. To reveal how the finite spanwise forcing is coupled with the flow around the cylinder, three spanwise forcing wavelengths are considered, namely one, two, and three times of the cylinder diameter. Through distributed control, both the morphologic and dynamic features of the near wake are changed. The vortex shedding mode downstream of the forcing section can be converted from the original asymmetric form to a symmetric form, whereas the wake downstream of the no-forcing section is less influenced by the synthetic jets. Thus, the near-wake patterns and vortex dynamics vary in the spanwise direction according to the distributed forcing. In particular, the original large-scale Kármán vortex and streamwise vortex become smaller-scale vortices, and their spanwise characteristic length scale resembles the distributed forcing wavelength. This spanwise modulation by the proposed control strategy demonstrates that the lift fluctuations could be suppressed and the mean drag could be reduced, though this will be affected by the spanwise forcing wavelength.