Due to the development of intermittent renewable energy resources, hydropower plants are mostly operated under off-design conditions. This may lead to natural frequency excitation shortening the turbine life-span. To accurately estimate the fatigue life, it is necessary to evaluate the hydrodynamic damping parameters. In the present study, different flow regimes and their relationship with hydrodynamic damping are analyzed numerically using the 3 - Reθt transition SST ĸ - ω turbulence model. The test case is a NACA0009 hydrofoil pitching around its center of mass. A good agreement between the present and previous numerical results is obtained. Consistent with the literature, hydrodynamic damping coefficient demonstrate consistently two different regions. The phase shift between the displacement and moment increases with the rise of the pitching frequency. After reaching a peak value at a reduced frequency of around κ = 5, the phase shift starts to decrease, and eventually approaches zero again. The damping behavior demonstrates an opposite trend. First, it reduces in spite of the phase shift increase, and after the inflection point, where the flow field changes from the drag mode to the thrust mode, it rises due to the torque development. The maximum of the damping occurs at the low frequencies.

This study investigates the physical mechanisms behind added mass and added damping during the transverse oscillation of a two-dimensional (2D) plate in a quiescent fluid. Added mass and added damping are defined as the components of the force in-phase and out-of-phase with the solid's acceleration, respectively. To achieve this goal, the force between the fluid and the solid is decomposed into physically meaningful components, establishing a direct link between the phenomena responsible for force generation and the added parameters. The study reveals that the added damping is solely dependent on vortex-induced and viscous forces, while added mass is predominantly influenced by inertia but also exhibits a significant contribution from vortex-induced and viscous forces. The results show that dimensionless frequency (⁠ β⁠) significantly influences added mass and added damping at low frequencies, with its impact decreasing as frequency increases. Additionally, added damping increases as the plate thickness ratio decreases, primarily due to the enhancement of the vortex-induced force mechanism. Reducing the thickness ratio (Δ) from Δ = 0.04 to Δ = 0.01 results in an increase in the damping coefficient by up to 60% within the intermediate range of the Keulegan–Carpenter (⁠KC⁠) number studied.