Experiments of Vortex-Induced Torsional Oscillation of a Flat Plate in Cross Flow

摘要

The authors describe experiments of the torsional oscillations due to vortex-induced vibrations (VIV) of a flat plate exposed to a normal cross flow. Such cross-flow VTV may be present in parked wind-turbine blades. Synchronous behavior, also known as lock-in behavior, occurs when the frequency of shedding vortices approaches a frequency of the structure, leading to a critical wind velocity at which adverse vibrations occur. The authors show lock-in behavior occurs not only at f_(vs) ≈ f_(vac) but also for a much broader wider range of frequencies. In the lock-in range, the shedding frequency from the vibrating structure synchronizes with the vibration frequency of the structure. Large-amplitude vibration may not occur in the entire lock-in range but may only occur at the relatively narrow range at which f_(vs) ≈ f_(vac) ≈f_(vib). Lock-in behavior differs from mechanical resonance behavior by considering the broad range of frequency synchronization, yet it is similar to mechanical resonance by considering the growth in the amplitude of vibration.