Wind Turbine Wakes Research Papers (original) (raw)

Flow past a square cylinder with and without corner modifications is carried out numerically by using CFD
fluent. The wake is generated by a uniform flow of Reynolds number (Re) 150 based on the characteristic
length of the cylinder, D. 2D unsteady numerical simulation is done using FVM employing pressure based
solver and PISO scheme. A computational grid independence study has been done to obtain a grid resolution
which predicts the results without any discrepancies. The flow separation point for the square cylinder with and
without corner modifications is obtained. The pressure distribution in the near wake region and around the
square cylinder surface is also investigated for different corner geometries. The results are presented in the
form of coefficient of pressure Vs Domain length/D, Coefficient of pressure along the cylinder wall and wall
shear stress along the cylinder wall. The results indicate that the flow separation in case of square cylinder
without sharp corners is delayed. The adverse pressure gradient along the surface of the cylinder and in the
near wake region is smaller for round corners. The tangential velocity of square cylinder with sharp corners is
large when compared with modified corners.
Keywords: Square Cylinder, Corner modifications, Reynolds number, wake, grid independence, flow
separation point, Pressure distribution, Lift coefficient, Drag coefficient.

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- CFD and numerical grid generation, Wind Turbine Wakes, Lift Coefficient, Drag Coefficient

This work deals with wind energy exploitation in complex terrain. The topic in general poses several scientific challenges about the comprehension of wind flow on its own and of the interaction of the wind flow with the wind turbines. In particular, in this work the focus is about wake effects in complex terrain. The selected test case is a cluster of four 2.3 MW wind turbines sited in Italy a very complex terrain. Their behavior is analyzed through Supervisory Control And Data Acquisition (SCADA) data mining and the relevant role of the terrain in distorting the wake of the upstream turbines is observed. These experimental evidences stimulate a deeper comprehension through numerical modeling: Computational Fluid Dynamics (CFD) simulations are run, where the presence of the wind turbines is accounted for through the Actu-ator Disk (AD) model. A novel way of elaborating the output of the simulations is proposed in this work, providing insight into the three-dimensional evolution of the wake proceeding downstream. The main outcome of the numerical analysis is that the terrain distorts the wind flow so that the wake profile is severely asymmetric with respect to the lateral displacement. These results identify the selected test case as an ideal testing ground for further analysis about yawing, mechanical loads and fatigue behavior in complex terrain.

- by Davide Astolfi
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- Engineering, Mechanical Engineering, Renewable Energy, Wind Energy

Wind turbine wakes in the atmosphere are three-dimensional (3D) and time dependent. An important question is how best to measure atmospheric wake properties, both for characterizing these properties observationally and for verification of numerical, conceptual, and physical (e.g., wind tunnel) models of wakes. Here a scanning, pulsed, coherent Doppler lidar is used to sample a turbine wake using 3D volume scan patterns that envelop the wake and simultaneously measure the inflow profile. The volume data are analyzed for quantities of interest, such as peak velocity deficit, downwind variability of the deficit, and downwind extent of the wake, in a manner that preserves the measured data. For the case study presented here, in which
the wake was well defined in the lidar data, peak deficits of up to 80% were measured 0.6–2 rotor diameters (D) downwind of the turbine, and the wakes extended more than 11D downwind. Temporal wake variability over periods of minutes and the effects of atmospheric gusts and lulls in the inflow are demonstrated in the analysis. Lidar scanning trade-offs important to ensuring that the wake quantities of interest are adequately sampled by the scan pattern, including scan coverage, number of scans per volume, data resolution, and scancycle repeat interval, are discussed.

- by Robert Banta and +2
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- Wind Energy, LiDAR, Wind turbine, Wake Turbulence
- by kiran bhaganagar
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- Engineering, Physical sciences, Wind Turbine Wakes, ENERGIES

Even if wind energy technology is nowadays fully developed, the use of wind energy in very complex terrain is still challenging. In particular, it is challenging to characterize the combination effects of wind flow over complex terrain and wake interactions between nearby turbines and this has a practical relevance too, for the perspective of mitigating anomalous vibrations and loads as well improving the farm efficiency. In this work, a very complex terrain site has been analyzed through a Reynolds-averaged CFD (Computational Fluid Dynamics) numerical wind field model; in the simulation the influence of wakes has been included through the Actuator Disk (AD) approach. In particular, the upstream turbine of a cluster of 4 wind turbines having 2.3 MW of rated power is studied. The objective of this study is investigating the full three-dimensional wind field and the impact of three-dimensionality on the evolution of the waked area between nearby turbines. A post-processing method of the output of the CFD simulation is developed and this allows to estimate the wake lateral deviation and the wake width. The reliability of the numerical approach is inspired by and crosschecked through the analysis of the operational SCADA (Supervisory Control and Data Acquisition) data of the cluster of interest.

- by Davide Astolfi and +1
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- Engineering, Mechanical Engineering, Renewable Energy, Wind Energy

- by Nezmin Kayedpour
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- Wind Energy, Wind Farm, Wind Turbine Wakes
- by Arne Gravdahl and +1
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- Wind Energy, Wind Turbine Wakes, Offshore Wind Farm
- by Bughsin Djath
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- Wind Energy, Atmospheric sciences, Offshore Wind Energy, Wind Farms
- by Giorgio Crasto
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- Wind Energy, Wind Turbine Wakes, Offshore Wind Farm, Elsevier

Turbulence structure in the wake behind a full-scale horizontal-axis wind turbine
under the influence of real-time atmospheric inflow conditions has been investigated using
actuator-line-model based large-eddy-simulations. Precursor atmospheric boundary layer
(ABL) simulations have been performed to obtain mean and turbulence states of the
atmosphere under stable stratification subjected to two different cooling rates. Wind
turbine simulations have revealed that, in addition to wind shear and ABL turbulence,
height-varying wind angle and low-level jets are ABL metrics that influence the structure
of the turbine wake. Increasing stability results in shallower boundary layers with stronger
wind shear, steeper vertical wind angle gradients, lower turbulence, and suppressed vertical
motions. A turbulent mixing layer forms downstream of the wind turbines, the strength and
size of which decreases with increasing stability. Height dependent wind angle and
turbulence are the ABL metrics influencing the lateral wake expansion. Further, ABL
metrics strongly impact the evolution of tip and root vortices formed behind the rotor.
Two factors play an important role in wake meandering: tip vortex merging due to the
mutual inductance form of instability and the corresponding instability of the turbulent
mixing layer

The present work considers an experimental investigation of wind turbine near wake by using Particle Image Velocimetry (PIV) visualization technique. The PIV technique gives a complete picture of all points at the domain under consideration. The study is focused on the effect of tip speed ratio () and Reynolds number (Re c ) on the near wake characteristics. A threeblade model of wind turbine with airfoil SG 6040 16% is tested in water channel at Re c range between 1.28 ×10 . Various tip speed ratios are tested between =2 and =12. Experiments are also performed at constant =8 and variable Re c 4 and 7.68 ×10 4 1 in the range between 2.56 ×10 and 5.12 ×10 4 . The results show that as  increases both wake width and length increase up to =9. For higher values of l, the wake width remains constant. The turbulence intensity measurements show that an increase of causes an increase of turbulence intensity in the wake. Experiments at constant tip speed ratio λ = 8 and variable Reyno...

Large-scale offshore wind farms are growing considerably fast in Europe. Optimal operational strategies are needed to improve the economic and reliability conditions of these sources. Maximising the total energy production, minimising the operating costs, and providing grid balancing services to transmission system operators are potential objectives of the optimal problem. This paper deals with an optimal operation strategy, which intends to optimise the operation of the whole wind farm by operating some wind turbines at sub-optimum points instead of optimising the power extraction of each wind turbine individually without considering the wake effect inside the wind farm. The wake formation can be minimised by reducing the wind turbine thrust force. Therefore, the axial induction based wake control can be achieved by adjusting the pitch angle and rotor speed, which results in an optimal tip speed ratio. In this work, we use the FLORIS model, which predicts the time-averaged three-dimensional flow field and turbine power capture of a wind farm as a function of the turbine control settings and the incoming wind field. The proposed approach is performed to analyse the axial induction control results in increased energy production. The analysis of the simulations of the C-Power phase one offshore wind farms in the North Sea indicates that the wake controlled strategy using axial induction control results in increased energy production.

- by Lieven Vandevelde and +1
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- Wind Energy, Wind Farm, Wind Turbine Wakes

This work deals with wind flow over complex terrain. The phenomenon is investigated by the point of view of wind farms operating in harsh environments. Therefore, peculiar attention is devoted to the combination effects of the complexity of the terrain and of wake effects and, for this reason, the proposed approach is numerical as well and experimental. Actually, this work deals with a test case wind farm sited in Italy in a very complex terrain. A cluster of 4 turbines having 2.3 MW of rated power is studied when the wind blows from West. Computational Fluid Dynamics (CFD) simulations are run on different set ups, in order to disentangle the effect of the terrain from that of wakes. Supervisory Control And Data Acquisition (SCADA) data sets are post processed in order to resemble experimentally the numerical set ups. It is shown that the numerical and experimental frameworks agree in the interpretation of the effects of terrain and wakes: the terrain distorts northward the wake of the upstream turbine, while multiple wakes contribute with an opposite tendency.

- by Davide Astolfi
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- Engineering, Mechanical Engineering, Computational Fluid Dynamics, Wind Energy