Modification of effective angle of attack on hydrofoil power extraction. (15th November 2021)

• Record Type: Journal Article
• Authors: He, Guanghua; Mo, Weijie; Gao, Yun; Zhang, Zhigang; Wang, Jiadong; Wang, Wei; Liu, Pengfei; Ghassemi, Hassan
• Is Part Of: Ocean engineering. Volume 240(2021)
• Publication Date: 2021-11-15
• Subjects: Oscillating hydrofoil turbine -- OpenFOAM -- Sliding interface -- Effective angle of attack; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2021.109919
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: A hydrofoil turbine with simultaneous heaving and pitching is found to have an ability to achieve a high power extraction. An OpenFOAM-based numerical model combined with a non-conformal sliding interface is employed to study the power extraction efficiency of a two-dimensional single hydrofoil. The developed numerical model is validated with the published experimental and numerical results. For Re = 500, 000, the energy extraction efficiencies of a single hydrofoil are mapped in the frequency and pitching amplitude domain. The numerical results show that the maximum of energy extraction efficiency can be reached up to 39%. The effective AoA (angle of attack) has a significant effect on the efficiency of energy extraction. The lift coefficient can be predicted much better based on the expression of the effective AoA considering the pitching angular velocity. Therefore, the pitching trajectory is calculated iteratively, and the better synchronization between the lift and the heaving velocity can improve the efficiency of energy extraction very effectively. When the effective AoA profiles are changed to the trapezoid ones, the higher efficiencies are achieved. Furthermore, the pitching trajectory obtained by the iteration is fitted to the harmonic function, and the phase differences between the fitted pitching and the heaving motion are ranged from 105° to 110° when the reduced frequency and heaving amplitude ratio are 0.14 and 1.0, respectively. Highlights: An OpenFOAM-based model is established to investigate the influence of the effective AoA on the energy extraction efficiency. It is found that the pitch rate has a non-negligible effect in the formula of effective AoA. A well-phased lift coefficient and a higher efficiency are achieved by adjusting pitching trajectory.