On the spectral behaviour of the turbulence-driven power fluctuations of horizontal-axis turbines

• Published in: Journal of fluid mechanics Vol. 904
• Main Authors: Deskos, Georgios, Payne, Grégory S., Gaurier, Benoît, Graham, Michael
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.12.2020; Cambridge University Press (CUP)
• Subjects: Aerodynamics; Axial flow; Computational fluid dynamics; Deceleration; Diameters; Energy; Energy spectra; ENGINEERING; Engineering Sciences; Flow velocity; Fluctuations; Fluid flow; Fluids mechanics; Flumes; horizontal-axis turbines; Hydrodynamics; Hypotheses; JFM Papers; Low pass filters; Mathematical models; Mechanics; power fluctuations; Power spectra; rotationally-sampled spectra; Rotors; Spectra; Turbine engines; Turbines; Turbulence; Velocity; Wind farms; Wind power; flow–structure interactions
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2020.681

In this article we consider the spectral behaviour of turbulence-driven power fluctuations for a single horizontal-axis turbine. To this end, a small-scale instrumented axial-flow hydrokinetic turbine model ($\textrm {diameter}=0.724\ \textrm {m}$) is deployed in the long water flume situated in the laboratory facilities of IFREMER in Boulogne-sur-Mer, France, and synchronous measurements of the upstream velocity and the rotor are collected for different tip-speed ratios. The study confirms previous findings suggesting that the power spectra follow the velocity spectra behaviour in the large scales region and a steeper power law slope behaviour ($-11/3$) over the inertial frequency sub-range. However, we show that both the amplitude of the power spectra and low-pass filtering effect over the inertial sub-range also depend on the rotor aero/hydrodynamics (e.g. $\mathrm {d}C_L/\mathrm {d}\alpha$) and the approaching flow deceleration and not solely on the rotational effects. In addition, we present a novel semi-analytical model to predict the dominant blade-passing frequency harmonics in the high-frequency regime using the rotationally sampled spectra technique. For all calculations, the distortion of incoming turbulence is taken into account.