Wake and power fluctuations of a model wind turbine subjected to pitch and roll oscillations

Fu, Sizu; Jin, Yaqing; Zheng, Yuan; Chamorro, Leonardo P.

doi:10.1016/j.apenergy.2019.113605

Cited by 62 publications

(43 citation statements)

References 26 publications

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“…Hu et al (2015) utilized a 1/300 Froude-scaled wind turbine model and a 3-DOF motion simulator in a wind tunnel to assess the influence of surge motion on structural loads and its effect on the near wake (x/D < 2, PIV measurements). Wind tunnel tests were conducted by Fu et al (2019) to quantify the effect of pitch and roll oscillations on power output and wake of a turbine model. In this case, rotor thrust was not measured.…”

Section: Introductionmentioning

confidence: 99%

“…Among the goals of these experiments was to investigate the effect of aerodynamic turbine loads on the global response of the system. Goupee et al (2012) investigated at 1/50 scale the response of three 5 MW FOWTs to wind and wave excitation. The blades of the turbine model were a geometrically scaled version of the NREL 5 MW blade, and the aerodynamic performance (thrust and power) of the rotor was not representative of the full-scale turbine.…”

Section: Introductionmentioning

confidence: 99%

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UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

et al. 2021

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Abstract. Floating offshore wind turbines are subjected to large motions due to the additional degrees of freedom of the floating foundation. The turbine rotor often operates in highly dynamic inflow conditions, and this has a significant effect on the overall aerodynamic response and turbine wake. Experiments are needed to get a deeper understanding of unsteady aerodynamics and hence leverage this knowledge to develop better models and to produce data for the validation and calibration of existing numerical tools. In this context, this paper presents a wind tunnel experiment about the unsteady aerodynamics of a floating turbine subjected to surge motion. The experiment results cover blade forces, rotor-integral forces, and wake. The 2D sectional model tests were carried out to characterize the aerodynamic coefficients of a low-Reynolds-number airfoil with harmonic variation in the angle of attack. The lift coefficient shows a hysteresis cycle close to stall, which grows in strength and extends in the linear region for motion frequencies higher than those typical of surge motion. Knowledge about the airfoil aerodynamic response was utilized to define the wind and surge motion conditions of the full-turbine experiment. The global aerodynamic turbine response is evaluated from rotor-thrust force measurements, because thrust influences the along-wind response of the floating turbine. It is found that experimental data follow predictions of quasi-steady theory for reduced frequency up to 0.5 reasonably well. For higher surge motion frequencies, unsteady effects may be present. The turbine near wake was investigated by means of hot-wire measurements. The wake energy is increased at the surge frequency, and the increment is proportional to the maximum surge velocity. A spatial analysis shows the wake energy increment corresponds with the blade tip. Particle image velocimetry (PIV) was utilized to visualize the blade-tip vortex, and it is observed that the vortex travel speed is modified in the presence of surge motion.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

et al. 2021

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“…The method suggested to achieve this is individual rotor yaw since it is a well‐established technique; however, the effects of rotor tilt are also of interest 51,52 and could be examined in further works. The effects of pitch and roll in floating turbines may also be applied to the multirotor case, as has been investigated in single rotor wind tunnel studies (for example, 53‐56 ) and numerical studies of Xiao and Yang 57 . More than this, the impacts of different atmospheric boundary layers 58‐60 and wave structures 61 on turbine wakes may also be extended to multirotor studies.…”

Section: Introductionmentioning

confidence: 99%

Wake steering of multirotor wind turbines

et al. 2021

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In this paper, wake steering is applied to multirotor turbines to determine whether it has the potential to reduce wind plant wake losses. Through application of rotor yaw to multirotor turbines, a new degree of freedom is introduced to wind farm control such that wakes can be expanded, channelled or redirected to improve inflow conditions for downstream turbines. Five different yaw configurations are investigated (including a baseline case) by employing large‐eddy simulations (LES) to generate a detailed representation of the velocity field downwind of a multirotor wind turbine. Two lower‐fidelity models from single‐rotor yaw studies (curled‐wake model and analytical Gaussian wake model) are extended to the multirotor case, and their results are compared with the LES data. For each model, the wake is analysed primarily by examining wake cross‐sections at different downwind distances. Further quantitative analysis is carried out through characterisations of wake centroids and widths over a range of streamwise locations and through a brief analysis of power production. Most significantly, it is shown that rotor yaw can have a considerable impact on both the distribution and magnitude of the wake velocity deficit, leading to power gains for downstream turbines. The lower‐fidelity models show small deviation from the LES results for specific configurations; however, both are able to reasonably capture the wake trends over a large streamwise range.

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“…The quantification of wake fluctuations provides insights for estimating the unsteadiness of power outputs of downstream turbines; this information is characterized by the turbulence kinetic energy TKE = ⟨u ′2 + w ′2 ⟩ 2U 2 hub shown in Figure 9; here, u ′2 and w ′2 are the velocity fluctuations in streamwise and spanwise directions and ⟨.⟩ denotes the time-average. Due to the limitation of two-dimensional PIV measurement, the velocity fluctuations in the y-axis component is not included [35,44]. This quantity illustrates the strong fluctuations of wake velocity due to the influence of α.…”

Section: Wake Characteristicsmentioning

confidence: 99%

The Influence of Winglet Pitching on the Performance of a Model Wind Turbine: Aerodynamic Loads, Rotating Speed, and Wake Statistics

2020

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The objective of this study is to investigate the influence of winglet pitching as an aero-brake on the performance of a model wind turbine by wind tunnel experiments. Time-resolved particle image velocimetry, force sensor, and datalogger were used to characterize the coupling between wake statistics, aerodynamic loads, and rotation speed. Results highlighted that, for a winglet with 4% of the rotor diameter length, the increase of its pitching angle can significantly reduce the turbine rotation speed up to ∼28% and thrust coefficient of ∼20%. The winglet pitching induced minor influence on the velocity deficit in the very near wake regions, while its influence on accelerating the wake recovery become clear around three diameters downstream the turbine rotor. The turbulence kinetic energy exhibited a distinctive increase under large pitching angles in the near wake region at the turbine hub height due to the strong vertical flow fluctuations. Further investigation on the spectra of wake velocities revealed that the pitching of winglet can suppress the high-pass filtering effects of turbines on wake fluctuations; such large-scale turbulence facilitated the flow mixing and accelerated the wake transport.

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Wake and power fluctuations of a model wind turbine subjected to pitch and roll oscillations

Cited by 62 publications

References 26 publications

UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

Wake steering of multirotor wind turbines

The Influence of Winglet Pitching on the Performance of a Model Wind Turbine: Aerodynamic Loads, Rotating Speed, and Wake Statistics

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