Kármán vortex formation from a cylinder: Role of phase-locked Kelvin–Helmholtz vortices

Abstract
The formation length of Kármán vortices can be drastically reduced by small‐amplitude excitation at a frequency much higher than the natural frequency of Kármán vortex formation, namely the Kelvin–Helmholtz (KH) frequency of the separating shear layer. Phase‐locked patterns of KH vortices are attainable. These spatially stationary patterns coexist, however, with the spatial and temporal development of the Kármán vortices.