Parameter Study of Dynamic Stall under High Reynolds Numbers

The increasing demand for renewable energy is driving the development of offshore wind turbines rating close to 20 MW. This results in an enormously large structure, challenging the verification prediction of aerodynamic loading and resulting structural integrity in the early design phase. Due to the pitching control and the modal motion of the long rotor blades, wind turbines are susceptible to dynamic stall. Large wind turbines are characterized as high Reynolds number and low modal frequencies, which have been scarcely studied. The recent studies describe distinct dynamic stall at these flow conditions, the delayed stall onset attributed to the enhanced flow attachment due to the early transition. In this study, extensive numerical simulations have been conducted to investigate the characteristics of dynamic stall in high Reynolds numbers. The URANS simulations feature FFA-W3-211 profile at Reynolds numbers of 3.75 − 15 × 10⁶ and reduced frequencies of 0.069 ≤ k ≤ 0.550, relevant to the large-scale wind turbines. Considering the large variation in altitude that large turbines encounter, different turbulent boundary conditions are examined as well. The the parameter study reveals that the sensitivity of dynamic stall to the parameter variations agrees well with the low Reynolds number studies. These findings can be used in the future to calibrate reduced-order models, which are applicable to offshore wind turbines in a large range of design and operating conditions.