Coherent structure in the turbulent wake behind a circular cylinder 2. Numerical simulation using the vortex filament model**Translated from Nagare, Journal of Japan Society of Fluid Mechanics 6 (1987) 124–131

Abstract

In the previous paper the authors reported observing the formation of a 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 Kánnán vortices. The 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 angle θ to the x–z plane (x is the mean flow direct and z the spanwise direction) with the width Zw, 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 the 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 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.