Spectral behaviour of the turbulence-driven power fluctuations of wind turbines

Tobin, Nicolas; Zhu, Hongni; Chamorro, Leonardo P.

doi:10.1080/14685248.2015.1031242

Cited by 51 publications

(74 citation statements)

References 36 publications

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“…The mean incoming velocity for all cases was U 0 = 8.5 m·s −1 , giving a Reynolds number based on the rotor diameter of Re = Ud/ν ∼ 7 × 10 4 , where ν is the kinematic viscosity, and a tip-speed ratio λ = ΩR/U 0 = 5. More details on the model turbine and its performance can be found in Tobin et al [22]. An active turbulence generator (TG) was used to induce large-scale and energetic coherent motions, resulting in high-turbulence (henceforth HT) intensity I HT = σ u /U 0 ≈ 11.5% at the turbine location.…”

Section: Methodsmentioning

confidence: 99%

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Effects of Freestream Turbulence in a Model Wind Turbine Wake

et al. 2016

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Abstract:The flow structure in the wake of a model wind turbine is explored under negligible and high turbulence in the freestream region of a wind tunnel at Re ∼ 7 × 10 4 . Attention is placed on the evolution of the integral scale and the contribution of the large-scale motions from the background flow. Hotwire anemometry was used to obtain the streamwise velocity at various streamwise and spanwise locations. The pre-multiplied spectral difference of the velocity fluctuations between the two cases shows a significant energy contribution from the background turbulence on scales larger than the rotor diameter. The integral scale along the rotor axis is found to grow linearly with distance, independent of the incoming turbulence levels. This scale appears to reach that of the incoming flow in the high turbulence case at x/d ∼ 35-40. The energy contribution from the turbine to the large-scale flow structures in the low turbulence case increases monotonically with distance. Its growth rate is reduced past x/d ∼ 6-7. There, motions larger than the rotor contribute ∼50% of the total energy, suggesting that the population of large-scale motions is more intense in the intermediate field. In contrast, the wake in the high incoming turbulence is quickly populated with large-scale motions and plateau at x/d ∼ 3.

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Section: Methodsmentioning

confidence: 99%

“…In the third region-dominated by very large scales-the power fluctuations are found to be directly influenced by the flow. Recently, Tobin et al [22] established a tuning-free model for the transfer function G( f ), which shows robust performance across wind turbine sizes spanning from laboratory models to MW scales.…”

Section: Introductionmentioning

confidence: 99%

Effects of Freestream Turbulence in a Model Wind Turbine Wake

et al. 2016

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“…The tower was made of a 4 mm diameter threaded steel rod. Refer to Tobin et al [17] for similar setup. The winglets are made by extending and bending the blade's tip with a 4 mm radius of curvature and 4 mm out-of-plane height, giving a winglet length ∼ 6.7% of the turbine radius, while maintaining the rotor radius as projected in the axial direction.…”

Section: Model Turbinesmentioning

confidence: 99%

An Experimental Study on the Effects ofWinglets on the Wake and Performance of a ModelWind Turbine

2015

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Wind tunnel experiments were performed to investigate the effects of downstream-facing winglets on the wake dynamics, power and thrust of a model wind turbine. Two similar turbines with and without winglets were operated under the same conditions. Results show an increase in the power and thrust coefficients of 8.2% and 15.0% for the wingletted case. A simple theoretical treatment of a two-turbine system suggests a possible positive tradeoff between increasing power and thrust coefficients at a wind farm scale. The higher thrust coefficient created a region of enhanced mean shear and turbulence in the outer portion of the wake. The winglets did not significantly change the tip-vortex strength, but higher levels of turbulence in the far wake decreased the tip-vortex strength. Because of the increased mean shear in the wingletted turbine's wake, the Reynolds stresses were higher, potentially leading to a higher energy flux downstream.

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“…They suggested that the spectral content of the power fluctuations, Φ P , and that of the incoming flow, Φ u , exhibit a relationship that can be characterized by a nonlinear transfer function G( f ) ∝ f −2 across relevant length scales. Recently, Tobin et al [8] introduced a tuning-free model for such transfer function G( f ) for single turbines, which was tested across turbine sizes. Overall, this implies that accurate estimation of Φ u is essential for the estimation of the corresponding structure of the power fluctuations of wind turbines.…”

Section: Introductionmentioning

confidence: 99%

On the Evolution of the Integral Time Scale within Wind Farms

et al. 2018

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A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale (T u ) within, and in the vicinity of, two model wind farms. The turbine arrays were placed over a rough wall and operated under high turbulence. The two layouts consisted of aligned units distinguished only by the streamwise spacing (∆x T ) between the devices, set at five and ten rotor diameters d T (or S x = ∆x T /d T = 5 and 10). They shared the same spanwise spacing between turbines of 2.5d T ; this resulted in arrays of 8 × 3 and 5 × 3 horizontal-axis turbines. Hotwire anemometry was used to characterize the instantaneous velocity at various vertical and transverse locations along the central column of the wind farms. Results show that T u was modulated by the wind farm layout. It was significantly reduced within the wind farms and right above them, where the internal boundary layer develops. The undisturbed levels above the wind farms were recovered only at ≈d T /2 above the top tip. This quantity appeared to reach adjusted values starting the fifth row of turbines in the S x = 5 wind farm, and earlier in the S x = 10 counterpart. Within the adjusted zone, the distribution of T u at hub height exhibited a negligible growth in the S x = 5 case; whereas it underwent a mild growth in the S x = 10 wind farm. In addition, the flow impinging the inner turbines exhibited T u /T u inc < 1, where T u inc is the integral time scale of the overall incoming flow. Specifically, T u → βT u inc at z = z hub , where β < 1 within standard layouts of wind farms, in particular β ≈ 0.5 and 0.7 for S x = 5 and 10.

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Spectral behaviour of the turbulence-driven power fluctuations of wind turbines

Cited by 51 publications

References 36 publications

Effects of Freestream Turbulence in a Model Wind Turbine Wake

Effects of Freestream Turbulence in a Model Wind Turbine Wake

An Experimental Study on the Effects ofWinglets on the Wake and Performance of a ModelWind Turbine

On the Evolution of the Integral Time Scale within Wind Farms

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