Influence of attack angle on the hydrodynamic damping characteristic of a hydrofoil

The present experiments are designed to investigate how an attack angle (0 degrees-6 degrees) influences the vortex-induced vibration and the corresponding hydrodynamic damping of a hydrofoil for three main modes, with a velocity ranging from 0 to 7.53 m/s. The feasibility of the experimental equipment and methods were verified. The results show that the lock-in region is wider for a larger attack angle, while no obvious change is found in the vortex shedding frequency in the lock-off region. The natural frequencies are barely affected by the flow velocity and attack angle in the lock-off region, while they increase slightly with increasing velocity in the lock-in region. The hydrodynamic damping ratio remains almost constant at different attack angles when the velocity is below the resonance velocity. When the velocity is above the resonance velocity, the trend of the hydrodynamic damping ratio increasing linearly with increasing velocity is independent of the attack angle, while the hydrodynamic damping ratio tends to decrease as the attack angle increases. The hydrodynamic damping ratio in the lock-in region is found to be negative, and the range of negative hydrodynamic damping increases, as the attack angle increases.