Vortex dynamics in a wire-disturbed cylinder wake

The effect of a thin control wire on the wake properties of the flow around a circular cylinder has been investigated numerically. The governing equations are solved using a spectral element method for a Reynolds number of Re(D)=100. The diameter ratio of the main cylinder and the wire equals D/d=50 so no vortex shedding is expected to occur for the wire. However, the vorticity introduced by the wire in the vicinity of the upper shear layer of the cylinder still affects the vortex dynamics in the wake of the main cylinder. The primary effect of the wire is the reduction of the velocity fluctuations in the vortex formation region of the main cylinder. The maximum decrement occurs at a wire position of y(w)/D=0.875. The secondary effect of the wire is observed in the kinematics of the vortices, leading to a modified vortex arrangement and strength difference between the upper and lower vortices. Due to these effects, for y(w)/D <= 0.875, a downward wake deflection is observed, while for larger values of y(w)/D>0.875, an upward deflection is found. The maximum downward deflection occurs at wire position y(w)/D=0.75 where the maximum positive mean lift coefficient, minimum drag coefficient, and minimum fluctuating lift coefficient are seen. Based on the observations, it is concluded that the deflection of the wake is primarily caused by a modification of the vortex arrangement in the wake. This modified vortex arrangement is caused by different formation times of the upper and lower vortices, by different vortex strengths, or by both. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466659]