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

Deskos, Georgios; Payne, Grégory S.; Gaurier, Benoît; Graham, J. M. R.

doi:10.1017/jfm.2020.681

Cited by 24 publications

(23 citation statements)

References 43 publications

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“…The phase relationship between the three blades ensures that the effect of the profile is negated at this frequency in the combined rotor load measurements-however, the effect of the profile can be observed in rotor quantities at the third harmonic of the rotational speed. This agrees with the findings of Section 4.3 and the findings of [19,39]. Given the effect of the profile on generating the dominant amplitude within the BRBM structures, it was expected that discrepancies between the amplitudes measured at the differing depths (and hence differing positions within the profiled flow) would be observed-however, this was not the case, suggesting that a more drastic profile is required before such significant changes in the BRBM spectra occur.…”

Section: Power Spectral Densitysupporting

confidence: 87%

“…There have been many laboratory studies into differing aspects of the three flow artefacts discussed above. There have been many articles focused on quantifying and modelling HATT power production under turbulent flow cases with a focus on spectral characterisation and modelling of loading and power production [6,14,15,[18][19][20][21][22][23][24][25][26]. Many laboratoryscale experiments detail the effects of upstream devices both in low turbulence and high turbulence scenarios with results presented in a phenomenological sense [6,14,15,17,27,28].…”

Section: Introductionmentioning

confidence: 99%

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A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

Allmark

Martínez

Ordóñez-Sánchez

et al. 2021

JMSE

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Tidal devices are likely to faced with shear flows and subjected to various wave climates. The paper presents an experimental study of the combined impacts of shear profile and irregular waves on the loading of a 1/20th scale device operating at peak power extraction. The experiments presented were conducted at various depths to facilitate analysis of the effects of the shear flow and wave impact on the device at various positions in the water column. The fluid field was measured at three different upstream positions and at three depths (top, middle and bottom of the rotor) for each experiment; in doing so, data from the device were captured three times. The fluid measurements were of a high quality and were analysed to present the structure flow upstream of the device, which contained velocity and turbulence profiles. The upstream measurement was utilised to understand the development of flow structures in the approach to the device, and the impact of the flow structures measured was confirmed via cross-covariance calculations. The long datasets gathered were used to produce full rotational probability density functions for the blade-root-bending moments for three blades. The spectral characteristics were also considered, and showed that rotor loading quantities are less reactive to smaller scale flow structures.

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Section: Power Spectral Densitysupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

Allmark

Martínez

Ordóñez-Sánchez

et al. 2021

JMSE

Self Cite

View full text Add to dashboard Cite

show abstract

“…In particular, it appears that the mean power generated by the turbine is insensitive to the inflow timescales at low tip-speed ratios, with the power curves resulting from the family of flows at constant I σ matching considerably for stalled flow around the blades. This turbine behaviour is unexpected, as previous research in the topic 21 finds that the turbine low-pass behaviour is not a property of the operating conditions.…”

Section: Fig 16 Dependence Of Power Due To Torque and Angular Velocmentioning

confidence: 63%

The effects of free-stream turbulence on the performance of a model wind turbine

Gambuzza

Ganapathisubramani

2021

Journal of Renewable and Sustainable Energy

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Free-stream turbulence characteristics play an important role in the mechanisms of power harvesting for wind turbines. Acquisitions of power and thrust from a model wind turbine of diameter 0.18 m have been carried out in a wind tunnel for a wide range of turbulent base flows, with varying free-stream turbulence intensity in the range between 3 % and 16 % and integral time scale spanning from 0.1 to 10 times the turbine rotation period. The results demonstrate that power is significantly affected both by the inflow turbulence scales and its intensity, while thrust is scarcely affected by free-stream turbulence. Fluctuations in the generated torques are also measured, with their behaviour dominated by the free-stream turbulence scale, and only moderately affected by turbulence intensity. The frequency response of thrust fluctuations has been measured for a selected subset of operating conditions, demonstrating that the turbine thrust is unaffected by high-frequency components in the inflow. Conclusions are drawn on the necessity to match both turbulence intensity and base flow frequency content in wind-tunnel studies if realistic results are to be obtained from small-scale studies.

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“…Earlier studies with tidal turbines reported a slope of −5/3 from the spectrum of the power output signal (e.g. Deskos et al 2020) resulting from the ambient turbulence governing the power fluctuation. However, our power spectra in figure 18 suggest that low-frequency changes in the power output of turbines in a large tidal array could be strongly affected by the wake meandering, depending on the turbine spacing and array layout.…”

Section: Turbine Loading Unsteadinessmentioning

confidence: 99%

Performance and wake characteristics of tidal turbines in an infinitely large array

Ouro

Nishino

2021

J. Fluid Mech.

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The efficiency of tidal stream turbines in a large array depends on the balance between negative effects of turbine-wake interactions and positive effects of bypass-flow acceleration due to local blockage, both of which are functions of the layout of turbines. In this study we investigate the hydrodynamics of turbines in an infinitely large array with aligned or staggered layouts for a range of streamwise and lateral turbine spacing. First, we present a theoretical analysis based on an extension of the linear momentum actuator disc theory for perfectly aligned and staggered layouts, employing a hybrid inviscid-viscous approach to account for the local blockage effect within each row of turbines and the viscous (turbulent) wake mixing behind each row in a coupled manner. We then perform large-eddy simulation (LES) of open-channel flow for 28 layouts of tidal turbines using an actuator line method with doubly periodic boundary conditions. Both theoretical and LES results show that the efficiency of turbines (or the power of turbines for a given bulk velocity) in an aligned array decreases as we reduce the streamwise turbine spacing, whereas that in a staggered array remains high and may even increase due to the positive local blockage effect (causing the local flow velocity upstream of each turbine to exceed the bulk velocity) if the lateral turbine spacing is sufficiently small. The LES results further reveal that the amplitude of wake meandering tends to decrease as we reduce the lateral turbine spacing, which leads to a lower wake recovery rate in the near-wake region. These results will help to understand and improve the efficiency of tidal turbines in future large arrays, even though the performance of real tidal arrays may depend not only on turbine-to-turbine interactions within the array but also on macro-scale interactions between the array and natural tidal currents, the latter of which are outside the scope of this study.

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

Abstract: Abstract

Cited by 24 publications

References 43 publications

A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

The effects of free-stream turbulence on the performance of a model wind turbine

Performance and wake characteristics of tidal turbines in an infinitely large array

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