Numerical study on aerodynamic characteristics and flow field of a circular cylinder equipped with a C-ring behind at Re=1000

Slender cylindrical structures such as cables and signal poles often experience vortex-induced vibrations. Recently, scholars have developed a novel mitigating measure by equipping a C-ring on the structures, where the C-ring is always behind the cylinder by tail rudder, but the mitigation mechanism is still unclear. To this end, the OpenFOAM((c)), an open source software, has been adopted in this study to carry out the large-eddy simulations (LES) to investigate the influence of a C-ring on the aerodynamic forces, surface pressure, and flow around a circular cylinder at Re = 1000, where the dynamic k-equation LES model is employed. Although the Re is far smaller than that in the reality, the aerodynamic characteristics and flow is also representative and worth studying in this subcritical range. Furthermore, to determine the appropriate radii (R) and arc lengths (theta) of the C-ring, various values of R (0.7D, 0.8D, 0.9D, and 1.0D, where D is diameter of the cylinder) and theta (60 degrees, 90 degrees, 120 degrees, 150 degrees, and 180 degrees) are considered and studied herein. The results indicate that a C-ring can reduce the SD of the lift coefficient by 40%-90% compared to that of a bare cylinder, whereas it has an unremarkable effect on the mean drag coefficient. The C-ring also has a significant influence on the fluctuating pressure coefficients, resulting in a small SD of the fluctuating lift. The spanwise flow on the leeward side of the cylinder under the influence of C-rings with different radii and arc lengths can be categorized into three modes. Meanwhile, the C-ring mitigates wind-induced vibrations by enhancing the spanwise flow on the leeward side of the cylinder. Finally, the appropriate parameters for the C-ring are recommended as follows: R = 0.7D and theta = 180 degrees; R = 0.8D and theta = 150 degrees; R = 0.9D and theta = 150 degrees; R = 1.0D and theta = 120 degrees, 150 degrees.