Investigation of wake characteristics for the offshore floating vertical axis wind turbines in pitch and surge motions of platforms

Pitch and surge motions of platforms are two main movements of offshore floating vertical axis wind turbines when they are faced with wind and wave loads. These two movements can not only affect the aerodynamic loads, but also may influence the wake characteristics of the wind turbines. In the present study, the computational fluid dynamics approach with the improved delayed detached eddy simulation (IDDES) and the overset mesh are employed to investigate the wake characteristics of an H-rotor floating vertical axis wind turbine under the platform's pitch and surge motions. The wake profiles and structures between pitch and non-pitch conditions, and surge and non-surge conditions are compared. Then, the wake characteristics under different pitching amplitudes and periods and different surging amplitudes and periods are investigated. It is shown that pitch motion can enlarge the peak values of wake deficits and shift the positions of the mainstream of the wake in the vertical direction. The amplitudes and periods of the 'wake wave' under different pitching amplitudes and periods show regular variations. A 'Spindle' -type of wake structure is formed in the wake region under a platform's surge motion, and the strength and core zone of the 'Spindle' also regularly change with different surging amplitudes and periods. These changes cause wake profile's diversity at certain motion stages for the same downwind distance under different periods and amplitudes of surge and pitch. (C) 2018 Elsevier Ltd. All rights reserved.