A study of the near wake structure of a wind turbine comparing measurements from laboratory and full-scale experiments

Whale, Jonathan; Papadopoulos, Kyriakos; Anderson, C.G.; Helmis, C. G.; Skyner, D.J.

doi:10.1016/0038-092x(96)00019-9

Cited by 66 publications

(42 citation statements)

References 6 publications

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“…3a we present an instantaneous velocity field, after subtracting the snowflake settling velocity W s from the original vector field to demonstrate the quality of our velocity measurements. The resulting velocity distribution reveals the dominant wake-flow features 2,12 , such as the travelling vortex cores, the momentum entrainment between vortices (highlighted in Fig. 3c), and the shear layer delineating the lower boundary between the turbine wake and the deflected incoming flow.…”

Section: Resultsmentioning

confidence: 99%

“…Particle image velocimetery (PIV), based on tracking the displacement of tracers in an illuminated flow field 10,11 , is the only measurement technique capable of obtaining planar velocity distributions with the spatio-temporal resolution required to study flow-structure interactions. However, PIV has only been applied, so far, to small-scale turbine models, from 0.1 m to a few metres in wind tunnel experiments [12][13][14][15][16][17] . One of the main obstacles to PIV implementation on a utility-scale turbine is the requirement to seed a large flow field (B100 m) with tracers uniformly and persistently distributed, in an environmentally benign, economic and non-intrusive fashion, which makes it almost impossible to use artificial seeding methods.…”

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confidence: 99%

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Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine

et al. 2014

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To improve power production and structural reliability of wind turbines, there is a pressing need to understand how turbines interact with the atmospheric boundary layer. However, experimental techniques capable of quantifying or even qualitatively visualizing the large-scale turbulent flow structures around full-scale turbines do not exist today. Here we use snowflakes from a winter snowstorm as flow tracers to obtain velocity fields downwind of a 2.5-MW wind turbine in a sampling area of B36 Â 36 m 2 . The spatial and temporal resolutions of the measurements are sufficiently high to quantify the evolution of bladegenerated coherent motions, such as the tip and trailing sheet vortices, identify their instability mechanisms and correlate them with turbine operation, control and performance. Our experiment provides an unprecedented in situ characterization of flow structures around utility-scale turbines, and yields significant insights into the Reynolds number similarity issues presented in wind energy applications.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine

et al. 2014

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“…Particle image velocimetry (PIV) measurements are able to yield the turbulence statistics of the wake flow and also reveal the detailed vortex structure of the wake by mapping the vorticity contours. One of the earliest applications of PIV to study wind turbine wakes is by Whale et al (1997). They measured mean and turbulent wake characteristics at distances of l.l and 1.5 rotor diameters away from the model turbine in the near wake and compared their results with full-scale data collected in the field.…”

Section: Introductionmentioning

confidence: 99%

“…Knowledge of wake development behind the turbine rotors is important for the minimization of wake interference effects and the optimization of wind turbine performance in wind farms. As Whale et al (1997) pointed out, the mean wake characteristics, their relation to the incident wind field and the local topography, influence the total energy resource at a potential wind farm site. Furthermore, the turbulence structure, and particularly the turbulence intensity distribution in the wake, affects the fatigue loading of downwind turbines.…”

Section: Introductionmentioning

confidence: 99%

Near-wake flow structure downwind of a wind turbine in a turbulent boundary layer

2011

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Wind turbines operate in the surface layer of the atmospheric boundary layer, where they are subjected to strong wind shear and relatively high turbulence levels. These incoming boundary layer flow characteristics are expected to affect the structure of wind turbine wakes. The near-wake region is characterized by a complex coupled vortex system (including helicoidal tip vortices), unsteadiness and strong turbulence heterogeneity. Limited information about the spatial distribution of turbulence in the near wake, the vortex behavior and their influence on the downwind development of the far wake hinders our capability to predict wind turbine power production and fatigue loads in wind farms. This calls for a better understanding of the spatial distribution of the 3D flow and coherent turbulence structures in the near wake. Systematic wind-tunnel experiments were designed and carried out to characterize the structure of the near-wake flow downwind of a model wind turbine placed in a neutral boundary layer flow. A horizontal-axis, three-blade wind turbine model, with a rotor diameter of 13 cm and the hub height at 10.5 cm, occupied the lowest one-third of the boundary layer. High-resolution particle image velocimetry (PIV) was used to measure velocities in multiple vertical streamwise planes (x-z) and vertical span-wise planes (y-z). In particular, we identified localized regions of strong vorticity and swirling strength, which are the signature of helicoidal tip vortices. These vortices are most pronounced at the top-tip level and persist up to a distance of two to three rotor diameters downwind. The measurements also reveal strong flow rotation and a highly non-axisymmetric distribution of the mean flow and turbulence structure in the near wake. The results provide new insight into the physical mechanisms that govern the development of the near wake of a wind turbine immersed in a neutral boundary layer. They also serve as important data for the development and validation of numerical models.

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“…Phase-locked particle image velocimetry (PIV) is now widely employed to measure flow statistics such as velocity (Hirahara et al, 2005;Lee and Wu, 2013), turbulence intensity (Whale et al, 1996;Liu et al, 2010), shear stress (Angele and MuhammadKlingmann, 2006;Stafford et al, 2012), and vorticity (Whale et al, 2000;Jin et al, 2014), and to subsequently identify large-scale coherent flow structures. Compared with traditional PIV, time resolved particle image velocimetry (TRPIV) has a higher sampling frequency and can grasp more detailed information of flow structures.…”

Section: Introductionmentioning

confidence: 99%

Time resolved particle image velocimetry experimental study of the near wake characteristics of a horizontal axis wind turbine

Wang

Yuan

Dong

et al. 2015

J. Zhejiang Univ. Sci. A

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Abstract:Wind tunnel experiments at a model scale have been carried out to investigate the flow characteristics in the near wake of a wind turbine. Time resolved particle image velocimetry (TRPIV) measurements are applied to visualize the wind turbine wake flow. The instantaneous vorticity, average velocities, turbulence kinetic energy, and Reynolds stresses in the near wake have been measured when the wind turbine is operated at tip speed ratios (TSRs) in the range of 3-5. It was found that wind turbine near the wake flow field can be divided into a velocity increased region, a velocity unchanged region, and a velocity deficit region in the radial direction, and the axial average velocities at different TSRs in the wake reach inflow velocity almost at the same radial location. The rotor wake turbulent kinetic energy appears in two peaks at approximately 0.3R and 0.9R regions in the radial direction. The Reynolds shear stress is less than the Reynolds normal stresses, the axial Reynolds normal stress is larger than the Reynolds shear stress and radial Reynolds normal stress in the blade root region, while the radial Reynolds normal stress is larger than the Reynolds shear stress and axial Reynolds normal stress in the blade tip region. The experimental data may also serve as a benchmark for validation of relevant computational fluid dynamics (CFD) models.

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A study of the near wake structure of a wind turbine comparing measurements from laboratory and full-scale experiments

Abstract: A study of the near wake structure of a wind turbine comparing measurements from laboratory and fullscale experiments. Solar Energy, 56 (6). pp. 621-633.

Cited by 66 publications

References 6 publications

Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine

Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine

Near-wake flow structure downwind of a wind turbine in a turbulent boundary layer

Time resolved particle image velocimetry experimental study of the near wake characteristics of a horizontal axis wind turbine

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