Dynamic response estimation for a variable-camber NACA0012 hydrofoil of a flapping-type tidal stream turbine

In this research, a camber changing mechanism feasible for use in a flapping hydrofoil tidal stream turbine is suggested to generate high lift force and subsequently a large flapping angle as a dynamic response. The hydrodynamic characteristics of rigid and variable-camber hydrofoils, which mainly affect the response, were numerically obtained using XFOIL. The flapping responses of the hydrofoils were estimated by a validated nonlinear dynamic model with the hydrodynamic characteristics. The estimated responses of a variable-camber hydrofoil were compared with the measured responses of the rigid hydrofoil from a previous study as well as the estimated responses of a rigid hydrofoil. It was shown from these comparisons that the variable-camber hydrofoil produced a much higher flapping angle amplitude with the same pitch angle relative to that of the rigid wing due to the cambered shape of the former. Moreover, the variable-camber hydrofoil could generate considerable flapping responses compared to experimental data, even when a relative small input pitch angle was applied in the estimation.