Abstract
In the previous paper the authors have observed the formation of spoon-shaped vortex chain in a wake behind a circular cylinder as a coherent structure in turbulence. In this report numerical simulation is carried out based on the assumption that the structure is formed by deformation of the Kármán vortices. Basic equation is the localized induction equation for a single vortex filament with an influence of the background mean flow. The vortex filament is given an initial deformation within a plane at an angleθ to x-z plane (x is the mean flow direction and z the spanwise direction) with the widthZw, and the further deformation process of the filament is numerically traced. The first calculation is made with fixed Zw, and various values of θ. The result shows that the vortex filament finally reaches a structure lying on a plane with a constant angle of 30°-45° to x-z plane irrespective of the initial values of θ. The second calculation is made with fixed θ and various values of Zw. In this case the final spanwise scale of the deformed region of the filament has an almost constant values of about 4d-6d (d is diameter of the cylinder). These results indicate that the final structure of the vortex filament is stable and definite irrespective of the initial disturbances.
