Transition zone of vortex wake modes and nonlinear dynamics in two-degree-of-freedom vortex-induced vibration of transmission conductors based on three-dimensional large eddy simulation

The vortex-induced vibration characteristics of transmission conductors under wind fields constitute a critical factor influencing structural safety. This study establishes a three-dimensional fluid–structure interaction numerical model based on the large eddy simulation method, systematically investigating the two-degree-of-freedom vibration characteristics of transmission conductors in pulsating wind fields. The vibration process evolves through four distinct stages: initial small-amplitude steady state, frequency-locked large-amplitude state, transitional modulation phase, and ultimately nonlinear chaotic stage under high wind speeds. The research reveals that within specific parameter ranges of reduced wind speed (4 < Ur< 5) and transverse displacement amplitude ratio (0.7 <Ay< 1) identified as the transition zone of vortex wake modes, the wake flow exhibits unique unsteady characteristics. This transition in vortex shedding patterns triggers significant fluid–structure interaction effects, resulting in substantial enhancement of alongwind displacement. Analysis of aerodynamic work shows that drag force performs predominantly positive work during lock-in and nonlinear stages, sustaining streamwise motion, while lift force does negative work at crosswind peaks, limiting lateral excursions. These findings clarify the multi-stage evolution of vortex-induced vibration, elucidate the wake-driven mechanism of high-amplitude vibration, and quantify the complementary roles of shear-layer instability and phase-dependent lift/drag work in governing conductor dynamics.