Effect of surge motion on the dynamic stall of floating offshore wind turbine airfoils

Floating offshore wind turbines (FOWTs) experience six degrees of freedom (6-DOF) motions due to wind, waves, and currents. The surge motion significantly affects the FOWT's aerodynamic performance and the flow field around the blade. The mechanism underlying the dynamic stall of the airfoil is complex. This paper analyzes the S809 airfoil. Four coupled pitch and surge motions are produced: upward surge and downward pitch (US&DP), &DP), downward surge and downward pitch (DS&DP), &DP), upward surge and upward pitch (US&UP), &UP), and downward surge and upward pitch (DS&UP). &UP). Two surge frequencies are considered: fy y = 0.083 Hz and fy y = 0.121 Hz. The analysis focuses on the effects of different coupled motions on the hysteresis response characteristics, the separation vortex on the airfoil surface, and load changes during the dynamic stall of the airfoil. The results indicate that the surge direction affects the dynamic stall trend of the airfoil. When the surge motion is upward, the airflow near the airfoil exerts a downward force on the boundary layer, preventing the generation of the separation vortex. A downward surge motion advances the stall, creates a large separation vortex, and results in a large hysteretic response of the flow field. The surge frequency affects the lift and drag amplitude, and the unsteady lift and drag coefficients increase with the surge frequency. The research results provide theoretical information for improving the safety and stability of FOWTs and valuable references for the design, optimization, and operation of wind turbines.