Numerical and experimental investigation of vortex formation modes on a freely vibrating circular cylinder at high Reynolds numbers

In this article, a series of investigations into the vortex-induced vibrations (VIV) of circular cylinders in the transverse direction is performed. The examinations focus on the Transition of Shear Layer 3 (TrSL3) flow regime, encompassing Reynolds numbers within the range of 3.4 x 104 <= Re <= 2.2 x 105, and explores the VIV responses at low mass ratios including one case for the infinite synchronization range. The study has captured the infinite resonance within this high Reynolds range through both experimental observation and computational cross-checking, highlighting its novelty. The study also examines mode transitions between branches through a combined approach of experimental and numerical analyses. Notably, a special phenomenon is uncovered wherein, at sufficiently low mass ratios, the upper branch of VIV synchronization continuously maintains. The numerical investigation broadly validates the experimental findings and also provides visualization into the modes of vortex formations. The outcomes of the investigation demonstrate a trend: as the mass ratio decreases, the oscillation amplitudes of the cylinder increase. Simultaneously, the synchronization range expands, eventually leading to the emergence of an indefinite upper branch when the mass ratio falls below a critical mass ratio of m*critical = 0.54. For the first time, this phenomenon is documented in the TrSL3 flow regime. The results broadly align with previous research in TrSL2 while the differences are highlighted in the corresponding sections.