Large-eddy simulation of two-degree-of-freedom vortex-induced vibration of a circular cylinder at Reynolds number 10 000

The canonical scenario of two-degree-of-freedom vortex-induced vibration (VIV) of a circular cylinder is re-examined in this study through high-fidelity large-eddy simulations (LES) at a Reynolds number of 10 000. The in-line and cross-flow vibration amplitudes, frequency responses and hydrodynamic coefficients predicted by the present LES match classical experimental results better than previous numerical attempts. In particular, motivated by an inadequate study yet vital importance of the small-amplitude in-line response in offshore engineering design, we present the first numerical evidence for the existence of three in-line response regions. Furthermore, the present in-line response agrees well with the design guideline DNV-RP-F105. After validating the present results against DNV-RP-F105 and published experiments, the detailed LES datasets enable further analysis of new VIV characteristics and physical mechanisms that have not been explored previously. For example, we identify and explain (i) the existence of twin governing frequencies for several VIV branches with partial synchronisation, (ii) decoupled in-line and cross-flow vibrations in the first in-line branch with symmetric vortex-shedding pattern, where an in-line resonance may not induce a cross-flow resonance, (iii) existence of a new elliptic vibration trajectory for a perfectly in-line resonant condition, (iv) gradualness in the 2S ↔ 2T transition of the vortex-shedding pattern and thus a continuous variation in the vibration amplitudes and hydrodynamic coefficients amid this transition and (v) lowest spanwise correlation of vortex shedding in the super-upper and lower branches, which is induced by complex interactions among ≥4 shed vortices over a cylinder vibration period.