Numerical simulation of transverse flow-induced vibrations of a D-section cylinder at low Reynolds number with varying angles of attack

Flow-induced vibrations (FIVs) of noncircular cylinders, particularly D-section bodies, frequently occur under low Reynolds number and low mass ratio conditions in applications, such as cables, risers, and microscale structures. Compared to circular cylinders, these configurations exhibit greater dynamic complexity and higher safety risks. At low Reynolds numbers, the interaction and transition between vortex-induced vibration (VIV) and galloping are still not sufficiently understood. This study numerically investigates the transverse FIV of a D-section cylinder at a Reynolds number of 100 and a mass ratio of 10, through reduced velocities from 2 to 20 and angles of attack from 0° to 180°. Five distinct vibration regimes are identified: typical VIV; transitional response I; small-amplitude VIV (S-VIV); transitional response II; and galloping. The results reveal that increasing the angle of attack progressively drives the system through multiple vibration regimes, transitioning from typical VIV, through intermediate states, to galloping. Lock-in, beating phenomena, and 2S vortex shedding dominate in the VIV regimes, while galloping exhibits persistent frequency separation, rising amplitudes, and multiple vortex shedding within one vibration cycle. Energetic analysis shows strong coupling between vibration and wake evolution, with frequency harmonics inducing anomalous amplitude peaks. These findings elucidate the underlying mechanisms that govern VIV–galloping transitions and underscore the critical role of angle of attack in determining the dynamic response.