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Fluid Mechanics and Turbulence in Wind Farms

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A3: Wind, Wave and Tidal Energy".

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 16548

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Dr. Richard Stevens

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Physics of Fluids Group, Max Planck Center Twente for Complex Fluid Dynamics, J. M. Burgers Center for Fluid Dynamics, and MESA+ Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
Interests: wind energy, wind farm dynamics, turbulence, atmospheric boundary layers, thermal convection, numerical simulations, large eddy simulations, direct numerical simulations, high-performance computing

Special Issue Information

Dear Colleagues,

We invite submissions to a Special Issue of the journal Energies on the topic of “Fluid Mechanics and Turbulence in Wind Farms”.

Wind energy is among the world's fastest growing renewable sources. Recent years have seen a rapid growth in the size of commercially constructed and operated wind farms, both in the turbine size used as well as the number of turbines employed. The interaction of large wind farms with the atmospheric boundary layer leads to unique wind-turbine array boundary layer dynamics, which need to be better understood. The tremendous amount of length scales involved in this problem involves huge challenges from an experimental, modeling, and simulation point of view. The aim is to obtain a better understanding of the physics that determine wind farm performance in an attempt to improve performance. To address these issues, it is necessary to perform field measurement campaigns, wind tunnel measurements, novel wind farm modeling strategies, and different wind farm simulations.

For this Special Issue, we would like to encourage original contributions regarding recent developments on and results relating to field measurements, wind tunnel experiments, analytical and engineering wind farm models, and simulations of wind farms. Potential topics include, but are not limited to, the following: wind farm performance, LiDAR and SCADA measurements, wind tunnel measurements, wake effects, effects of thermal stability conditions of the boundary layer (stable and unstable conditions), Coriolis effects, diurnal cycle, gravity waves, effects of wind–wave interactions, wind farm control strategies, wind farm frequency regulation, complex terrain effects, effects of wind farms on meso-scale weather phenomena, farm-to-farm interactions, comparison studies, and wind farm performance forecasting.

Dr. Richard Stevens
Guest Editor

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Keywords

Wind farms
Power production
Wake effects
Turbulence intensity
Atmospheric boundary layer
Thermal effects
Wind farm control
Complex terrain
Diurnal cycle
Field measurements
Wind tunnel experiments
Numerical simulations
Large eddy simulations
Reynolds-averaged Navier–Stokes
Meso-scale wind farm modeling.

Published Papers (5 papers)

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Research

20 pages, 7667 KiB

Open AccessArticle

Distinct Turbulent Regions in the Wake of a Wind Turbine and Their Inflow-Dependent Locations: The Creation of a Wake Map

by Ingrid Neunaber, Michael Hölling, Richard J. A. M. Stevens, Gerard Schepers and Joachim Peinke

Energies 2020, 13(20), 5392; https://doi.org/10.3390/en13205392 - 15 Oct 2020

Cited by 22 | Viewed by 3778

Abstract

Wind turbines are usually clustered in wind farms which causes the downstream turbines to operate in the turbulent wakes of upstream turbines. As turbulence is directly related to increased fatigue loads, knowledge of the turbulence in the wake and its evolution are important. Therefore, the main objective of this study is a comprehensive exploration of the turbulence evolution in the wind turbine’s wake to identify characteristic turbulence regions. For this, we present an experimental study of three model wind turbine wake scenarios that were scanned with hot-wire anemometry with a very high downstream resolution. The model wind turbine was exposed to three inflows: laminar inflow as a reference case, a central wind turbine wake, and half of the wake of an upstream turbine. A detailed turbulence analysis reveals four downstream turbulence regions by means of the mean velocity, variance, turbulence intensity, energy spectra, integral and Taylor length scales, and the Castaing parameter that indicates the intermittency, or gustiness, of turbulence. In addition, a wake core with features of homogeneous isotropic turbulence and a ring of high intermittency surrounding the wake can be identified. The results are important for turbulence modeling in wakes and optimization of wind farm wake control. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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13 pages, 2372 KiB

Open AccessArticle

Wind Turbines with Truncated Blades May Be a Possibility for Dense Wind Farms

by Shyuan Cheng, Yaqing Jin and Leonardo P. Chamorro

Energies 2020, 13(7), 1810; https://doi.org/10.3390/en13071810 - 09 Apr 2020

Cited by 4 | Viewed by 2085

Abstract

We experimentally explored the impact of a wind turbine with truncated blades on the power output and wake recovery, and its effects within

2 \times 3

arrays of standard units. The blades of the truncated turbine covered a fraction of the outer region [...] Read more.

We experimentally explored the impact of a wind turbine with truncated blades on the power output and wake recovery, and its effects within

2 \times 3

arrays of standard units. The blades of the truncated turbine covered a fraction of the outer region of the rotor span and replaced with a zero-lift structure around the hub, where aerodynamic torque is comparatively low. This way, the incoming flow around the hub may be used as a mixing enhancement mechanism and, consequently, to reduce the flow deficit in the wake. Particle image velocimetry was used to characterize the incoming flow and wake of various truncated turbines with a variety of blade length ratios

L / R = 0.6

, 0.7, and 1, where L is the length of the working section of the blade of radius R. Power output was obtained at high frequency in each of the truncated turbines, and also at downwind units within

2 \times 3

arrays with streamwise spacing of

Δ x / d_{T} = 4,

5, and 6, with

d_{T}

being the turbine diameter. Results show that the enhanced flow around the axis of the rotor induced large-scale instability and mixing that led to substantial power enhancement of wind turbines placed 4

d_{T}

downwind of the

L / R = 0.6

truncated units; this additional power is still relevant at 6

d_{T}

. Overall, the competing factors defined by the expected power reduction of truncated turbines due to the decrease in the effective blade length, the need for reduced components of the truncated units, and enhanced power output of downwind standard turbines suggest a techno-economic optimization study for potential implementation. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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25 pages, 7284 KiB

Open AccessArticle

Dynamics of Large Scale Turbulence in Finite-Sized Wind Farm Canopy Using Proper Orthogonal Decomposition and a Novel Fourier-POD Framework

by Tanmoy Chatterjee and Yulia T. Peet

Energies 2020, 13(7), 1660; https://doi.org/10.3390/en13071660 - 02 Apr 2020

Cited by 5 | Viewed by 2475

Abstract

Large scale coherent structures in the atmospheric boundary layer (ABL) are known to contribute to the power generation in wind farms. In order to understand the dynamics of large scale structures, we perform proper orthogonal decomposition (POD) analysis of a finite sized wind turbine array canopy in the current paper. The POD analysis sheds light on the dynamics of large scale coherent modes as well as on the scaling of the eigenspectra in the heterogeneous wind farm. We also propose adapting a novel Fourier-POD (FPOD) modal decomposition which performs POD analysis of spanwise Fourier-transformed velocity. The FPOD methodology helps us in decoupling the length scales in the spanwise and streamwise direction when studying the 3D energetic coherent modes. Additionally, the FPOD eigenspectra also provide deeper insights for understanding the scaling trends of the three-dimensional POD eigenspectra and its convergence, which is inherently tied to turbulent dynamics. Understanding the behaviour of large scale structures in wind farm flows would not only help better assess reduced order models (ROM) for forecasting the flow and power generation but would also play a vital role in improving the decision making abilities in wind farm optimization algorithms in future. Additionally, this study also provides guidance for better understanding of the POD analysis in the turbulence and wind farm community. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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23 pages, 14080 KiB

Open AccessArticle

An Induction Curve Model for Prediction of Power Output of Wind Turbines in Complex Conditions

by Mohsen Vahidzadeh and Corey D. Markfort

Energies 2020, 13(4), 891; https://doi.org/10.3390/en13040891 - 17 Feb 2020

Cited by 6 | Viewed by 2468

Abstract

Power generation from wind farms is traditionally modeled using power curves. These models are used for assessment of wind resources or for forecasting energy production from existing wind farms. However, prediction of power using power curves is not accurate since power curves are based on ideal uniform inflow wind, which do not apply to wind turbines installed in complex and heterogeneous terrains and in wind farms. Therefore, there is a need for new models that account for the effect of non-ideal operating conditions. In this work, we propose a model for effective axial induction factor of wind turbines that can be used for power prediction. The proposed model is tested and compared to traditional power curve for a 2.5 MW horizontal axis wind turbine. Data from supervisory control and data acquisition (SCADA) system along with wind speed measurements from a nacelle-mounted sonic anemometer and turbulence measurements from a nearby meteorological tower are used in the models. The results for a period of four months showed an improvement of 51% in power prediction accuracy, compared to the standard power curve. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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18 pages, 9401 KiB

Open AccessEditor’s ChoiceArticle

Large-Eddy Simulation of Yawed Wind-Turbine Wakes: Comparisons with Wind Tunnel Measurements and Analytical Wake Models

by Mou Lin and Fernando Porté-Agel

Energies 2019, 12(23), 4574; https://doi.org/10.3390/en12234574 - 30 Nov 2019

Cited by 32 | Viewed by 4519

Abstract

In this study, we validated a wind-turbine parameterisation for large-eddy simulation (LES) of yawed wind-turbine wakes. The presented parameterisation is modified from the rotational actuator disk model (ADMR), which takes account of both thrust and tangential forces induced by a wind turbine based on the blade-element theory. LES results using the yawed ADMR were validated with wind-tunnel measurements of the wakes behind a stand-alone miniature wind turbine model with different yaw angles. Comparisons were also made with the predictions of analytical wake models. In general, LES results using the yawed ADMR are in good agreement with both wind-tunnel measurements and analytical wake models regarding wake deflections and spanwise profiles of the mean velocity deficit and the turbulence intensity. Moreover, the power output of the yawed wind turbine is directly computed from the tangential forces resolved by the yawed ADMR, in contrast with the indirect power estimation used in the standard actuator disk model. We found significant improvement in the power prediction from LES using the yawed ADMR over the simulations using the standard actuator disk without rotation, suggesting a good potential of the yawed ADMR to be applied in LES studies of active yaw control in wind farms. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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