Flow-induced vibration of a locally rough cylinder with two symmetrical strips attached on its surface: effect of the location and shape of strips

The flow induced vibration of a circular cylinder selectively roughened with two strips is numerically investigated using a two-way fluid-structure interaction (FSI) approach at high Reynolds numbers (30480 ≤ Re ≤ 304800). The main purpose of the study is to evaluate the effect of the location and shape of strips on the vibration response. The numerical model is validated with the experimental and numerical results reported in previous studies. The results indicate that the response is sensitive to the placement angle and shape of strips. The 12 in. cylinder with rectangular strips at α = 20° has the similar response trend as the 3.5 in. cylinder. The gap between VIV and galloping is filled by placing strips in the front surface of the cylinder. Hard galloping zone 1 (HG1) appears at α = 20° and 60° where the amplitude grows quickly after the onset of galloping, and hard galloping zone 2 (HG2) appears at α = 0° and 74° where the amplitude grows relatively slowly. Among them, placing strips at α = 20° has the best performance in enhancing vibration. However, the vibration is suppressed by placing the rectangular strips at α = 120°, where the boundary layer separation point transfers to the strip surface. The galloping is observed using trapezoid I and II strips, while it is not achieved by placing triangular or arc strips. The changes in turbulent intensity, vortex shedding mode and wake width reflect the transition from VIV to galloping.