Vortex-induced vibration of a sinusoidal wavy cylinder: The effect of wavelength

While considerable research has addressed flow around stationary sinusoidal wavy cylinders, studies on vortex-induced vibration (VIV) of elastic-supported wavy cylinders still remain limited. This study aims to address this gap through a series of water tunnel experiments, focusing on the effects of the cylinder's spanwise wavelength. Three typical spanwise wavelengths (λ* = 1.8, 3.6, and 6.0) are considered, with the first and third identified as the optimal for reducing fluid forces (lift forces by over 90%) in previous stationary cylinder studies. The cylinder oscillates transversally at a range of reduced velocities Ur = 3.0–12.0, corresponding to the Reynolds numbers (1.5–7.0) × 103. Results indicate that, compared with a smooth cylinder, the λ* = 1.8 cylinder experiences reduced oscillation throughout the VIV regime, while the cylinders with λ* = 3.6 or 6.0 undergo enhanced oscillation over a broader lock-in range. The oscillation of the wavy cylinders with λ* = 3.6 or 6.0 tend to occur at a higher Ur, leading to an extension of the lower branch. Frequency analysis shows that, despite affecting vibration amplitude, the wavy surface retains typical VIV features. These results reveal a notable dependence of fluid forces and force-displacement phase lag on the cylinder's wavelength. Finally, we provide a detailed discussion of the phase-averaged and time-averaged flow structures from the time-resolved particle image velocimetry measurement. Overall, this study addresses the research gap concerning the impact of wavelength on the behavior of elastically supported wavy cylinders, providing significant insights for the development of practical strategies for VIV suppression and enhancement.