Streamwise evolution of an inclined cylinder wake

Abstract

The streamwise evolution of an inclined circular cylinder wake was investigated by measuring all three velocity and vorticity components using an eight-hotwire vorticity probe in a wind tunnel at a Reynolds number Red of 7,200 based on free stream velocity (U ∞) and cylinder diameter (d). The measurements were conducted at four different inclination angles (α), namely 0°, 15°, 30°, and 45° and at three downstream locations, i.e., x/d = 10, 20, and 40 from the cylinder. At x/d = 10, the effects of α on the three coherent vorticity components are negligibly small for α ≤ 15°. When α increases further to 45°, the maximum of coherent spanwise vorticity reduces by about 50%, while that of the streamwise vorticity increases by about 70%. Similar results are found at x/d = 20, indicating the impaired spanwise vortices and the enhancement of the three-dimensionality of the wake with increasing α. The streamwise decay rate of the coherent spanwise vorticity is smaller for a larger α. This is because the streamwise spacing between the spanwise vortices is bigger for a larger α, resulting in a weak interaction between the vortices and hence slower decaying rate in the streamwise direction. For all tested α, the coherent contribution to $$ \overline{{v^{2}}} $$ is remarkable at x/d = 10 and 20 and significantly larger than that to $$ \overline{{u^{2}}} $$ and $$ \overline{{w^{2}}}. $$ This contribution to all three Reynolds normal stresses becomes negligibly small at x/d = 40. The coherent contribution to $$ \overline{{u^{2}}} $$ and $$ \overline{{v^{2}}} $$ decays slower as moving downstream for a larger α, consistent with the slow decay of the coherent spanwise vorticity for a larger α.