Data-driven classification of flow modes in unsteady galloping and its applications in flow mechanisms

Galloping is a divergent behavior of bluff bodies under aerodynamic forces and should be strictly suppressed in civil engineering. Considering that most studies focus on unsteady vibration response and lift, neglecting the overall flow field structure and its fundamental modes, this study explores the applicability of dynamic mode decomposition in modes classification according to sources of excitation, explaining the flow mechanisms associated with galloping. First, the results of an ideal section demonstrate the presence of two distinct modes in the uniform flow involving fluid-solid coupling issues, instability-induced mode (IIM) and movement-induced mode, respectively. Second, galloping stability is primarily determined by the phase of the first movement-induced mode, which is also verified in the complex engineering sections. Third, the energy contribution of these modes is dependent on vibration amplitude. In the complex engineering section, galloping exhibits amplitude dependence near the critical state, whereas this behavior is absent in the ideal rectangular section. This difference is closely related to the complexity of the frequency components in the IIM. This study contributes to a deeper understanding of unsteady galloping dynamics, offering insights for both theoretical research and practical engineering applications.