Vortex-Induced vibration suppression for a cylinder with random grooves inspired by rough tree bark

The vortex-induced vibration (VIV) response of a 2-degree-of-freedom cylinder with random grooves is investigated numerically based on the Reynolds Average Navier-Stokes (RANS) method. The Newmark-beta method is used to solve the equations of motion of the cylinder. The effects of the random groove on VIV suppression are discussed in detail. The coverage ratios (k) of the random groove include 0%, 25%, 50%, 75%, and 100%. The vibration suppression effect of k = 75% and k = 100% is not significant. However, the VIV amplitude of the cylinders with k = 25% is greatly suppressed. In particular, the cross-flow amplitude ratio is reduced from 1.50 (k = 0%, a smooth cylinder) to 0.65 (k = 25%). First, the boundary-layer separation point of the grooves is fixed, so the random grooves destroy the normal separation and development of the main vortices. Therefore, two rows of vortices with different sizes are generated on both sides of the cylinder, which may cause unstable vibration. Meanwhile, a series of small vortices are formed in the grooves. These small vortices cannot merge synchronously into the main vortices and further reduced the strength of the main vortices. Consequently, the driving force of the vibration, which is generated by the main vortices, is reduced. As a result, the VIV responses are suppressed.