Wake Dynamics and VIV Suppression Mechanisms of Wavy Cylinders at Subcritical Reynolds Numbers

The wake formations behind wavy cylinders are numerically investigated in this study using large-eddy simulations. The drag force, lift fluctuations, velocity profiles, vortex formation length, and wake pressure coefficient are examined at a Reynolds number (Re = 3.9 × 10³) based on the mean diameter of the cylinder. Five wavy cylinder models, including single and double wavy configurations, are investigated with wavelength-to-diameter ratios (λ/Dₘ) ranging from 3.79 to 6.82. The numerical results of the wavy cylinders are compared with those of a smooth circular cylinder having an equivalent diameter. Significant differences in vortical structure patterns are observed between the wavy cylinders and the smooth circular cylinder. Owing to its wavy configuration, the double wavy cylinder achieves maximum reductions in drag and lift coefficients of 14.13% and 89.12%, respectively, compared with the smooth circular cylinder at λ/Dₘ = 6.06. This indicates that vortex-induced vibrations can be significantly suppressed at specific combinations of λ/Dₘ and a/Dₘ. The wake width of the double wavy (DW) cylinder expands in the downstream region compared with that of the single wavy (SW) cylinder, which in turn is larger than that of the smooth circular (SC) cylinder. The flow separation line along the wavy cylinders varies in the spanwise direction. The free shear layers of the wavy cylinders are more stable and extend further downstream than those of the SC cylinder, rolling up into vortices at a greater downstream distance as λ/Dₘ increases to 6.06. As a result, the vortex formation length is increased, and lift fluctuations are significantly suppressed through drag reduction. The fundamental mechanisms of force reduction, including the associated flow features, are discussed for different λ/Dₘ values.