A BEM-Based Actuator Disk Model for Wind Turbine Wakes Considering Atmospheric Stability

Atmospheric stability affects wind turbine wakes significantly. High-fidelity approaches such as large eddy simulations (LES) with the actuator line (AL) model which predicts detailed wake structures, fail to be applied in wind farm engineering applications due to its expensive cost. In order to make wind farm simulations computationally affordable, this paper proposes a new actuator disk model (AD) based on the blade element method (BEM) and combined with Reynolds-averaged Navier–Stokes equations (RANS) to model turbine wakes under different atmospheric stability conditions. In the proposed model, the upstream reference velocity is firstly estimated from the disk averaged velocity based on the one-dimensional momentum theory, and then is used to evaluate the rotor speed to calculate blade element forces. Flow similarity functions based on field measurement are applied to limit wind shear under strongly stable conditions, and turbulence source terms are added to take the buoyant-driven effects into consideration. Results from the new AD model are compared with field measurements and results from the AD model based on the thrust coefficient, the BEM-AD model with classical similarity functions and a high-fidelity LES approach. The results show that the proposed method is better in simulating wakes under various atmospheric stability conditions than the other AD models and has a similar performance to the high-fidelity LES approach however in much lower computational cost.

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LES of wind farm response to transient scenarios using a high fidelity actuator disk model

Journal of Physics Conference Series ◽

10.1088/1742-6596/753/3/032053 ◽

2016 ◽

Vol 753 ◽

pp. 032053 ◽

Cited By ~ 2

Author(s):

M Moens ◽

M Duponcheel ◽

G Winckelmans ◽

P Chatelain

Keyword(s):

Wind Farm ◽

High Fidelity ◽

Disk Model ◽

Actuator Disk

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Fatigue Life Analysis of Offshore Wind Turbine Support Structures in an Offshore Wind Farm

ASME 2018 1st International Offshore Wind Technical Conference ◽

10.1115/iowtc2018-1061 ◽

2018 ◽

Author(s):

Bryan Nelson ◽

Yann Quéméner

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Wind Farm ◽

The Body ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Analysis Tool ◽

Support Structures ◽

Offshore Wind Farm ◽

Actuator Disk

This study evaluated, by time-domain simulations, the fatigue lives of several jacket support structures for 4 MW wind turbines distributed throughout an offshore wind farm off Taiwan’s west coast. An in-house RANS-based wind farm analysis tool, WiFa3D, has been developed to determine the effects of the wind turbine wake behaviour on the flow fields through wind farm clusters. To reduce computational cost, WiFa3D employs actuator disk models to simulate the body forces imposed on the flow field by the target wind turbines, where the actuator disk is defined by the swept region of the rotor in space, and a body force distribution representing the aerodynamic characteristics of the rotor is assigned within this virtual disk. Simulations were performed for a range of environmental conditions, which were then combined with preliminary site survey metocean data to produce a long-term statistical environment. The short-term environmental loads on the wind turbine rotors were calculated by an unsteady blade element momentum (BEM) model of the target 4 MW wind turbines. The fatigue assessment of the jacket support structure was then conducted by applying the Rainflow Counting scheme on the hot spot stresses variations, as read-out from Finite Element results, and by employing appropriate SN curves. The fatigue lives of several wind turbine support structures taken at various locations in the wind farm showed significant variations with the preliminary design condition that assumed a single wind turbine without wake disturbance from other units.

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Utility-Scale Wind Turbine Wake Characterization Using Nacelle-Based Long-Range Scanning Lidar

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00218.1 ◽

2014 ◽

Vol 31 (7) ◽

pp. 1529-1539 ◽

Cited By ~ 25

Author(s):

Matthew L. Aitken ◽

Julie K. Lundquist

Keyword(s):

Wind Turbine ◽

Long Range ◽

Wind Farm ◽

Thrust Coefficient ◽

Velocity Deficit ◽

Scanning Lidar ◽

Range Scanning ◽

Utility Scale ◽

Turbine Wake ◽

Wind Turbine Wake

Abstract To facilitate the optimization of turbine spacing at modern wind farms, computational simulations of wake effects must be validated through comparison with full-scale field measurements of wakes from utility-scale turbines operating in the real atmosphere. Scanning remote sensors are particularly well suited for this objective, as they can sample wind fields over large areas at high temporal and spatial resolutions. Although ground-based systems are useful, the vantage point from the nacelle is favorable in that scans can more consistently transect the central part of the wake. To the best of the authors’ knowledge, the work described here represents the first analysis in the published literature of a utility-scale wind turbine wake using nacelle-based long-range scanning lidar. The results presented are of a field experiment conducted in the fall of 2011 at a wind farm in the western United States, quantifying wake attributes such as the velocity deficit, centerline location, and wake width. Notable findings include a high average velocity deficit, decreasing from 60% at a downwind distance x of 1.8 rotor diameters (D) to 40% at x = 6D, resulting from a low average wind speed and therefore a high average turbine thrust coefficient. Moreover, the wake width was measured to expand from 1.5D at x = 1.8D to 2.5D at x = 6D. Both the wake growth rate and the amplitude of wake meandering were observed to be greater for high ambient turbulence intensity and daytime conditions as compared to low turbulence and nocturnal conditions.

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Evaluation of Tip Loss Corrections to AD/NS Simulations of Wind Turbine Aerodynamic Performance

Applied Sciences ◽

10.3390/app9224919 ◽

2019 ◽

Vol 9 (22) ◽

pp. 4919 ◽

Cited By ~ 1

Author(s):

Wei Zhong ◽

Tong Guang Wang ◽

Wei Jun Zhu ◽

Wen Zhong Shen

Keyword(s):

Wind Turbine ◽

Wind Farm ◽

Relative Difference ◽

Superior Performance ◽

Navier Stokes ◽

Special Focus ◽

Actuator Disc ◽

Blade Tip ◽

Blade Loads ◽

Blade Element

The Actuator Disc/Navier-Stokes (AD/NS) method has played a significant role in wind farm simulations. It is based on the assumption that the flow is azimuthally uniform in the rotor plane, and thus, requires a tip loss correction to take into account the effect of a finite number of blades. All existing tip loss corrections were originally proposed for the Blade-Element Momentum Theory (BEMT), and their implementations have to be changed when transplanted into the AD/NS method. The special focus of the present study is to investigate the performance of tip loss corrections combined in the AD/NS method. The study is conducted by using an axisymmetric AD/NS solver to simulate the flow past the experimental NREL Phase Ⅵ wind turbine and the virtual NREL 5MW wind turbine. Three different implementations of the widely used Glauert tip loss function F are discussed and evaluated. In addition, a newly developed tip loss correction is applied and compared with the above implementations. For both the small and large rotors under investigation, the three different implementations show a certain degree of difference to each other, although the relative difference in blade loads is generally no more than 4%. Their performance is roughly consistent with the standard Glauert correction employed in the BEMT, but they all tend to make the blade tip loads over-predicted. As an alternative method, the new tip loss correction shows superior performance in various flow conditions. A further investigation into the flow around and behind the rotors indicates that tip loss correction has a significant influence on the velocity development in the wake.

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On Predicting the Phenomenon of Surface Flow Convergence in Wind Farms

Volume 3B: Oil and Gas Applications; Organic Rankine Cycle Power Systems; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2014-25307 ◽

2014 ◽

Cited By ~ 2

Author(s):

Suganthi Selvaraj ◽

Anupam Sharma

Keyword(s):

Wind Farm ◽

Wind Farms ◽

Surface Flow ◽

Maximum Efficiency ◽

Horizontal Axis Wind Turbine ◽

Disk Model ◽

Systematic Analysis ◽

Actuator Disk ◽

Momentum Theory ◽

Flow Convergence

A systematic analysis of a single-rotor horizontal axis wind turbine aerodynamics is performed to obtain a realistic potential maximum efficiency. It is noted that by including the effects of swirl, viscosity and finite number of blades, the maximum aerodynamic efficiency of a HAWT is within a few percentage points of the efficiency of commercially-available turbines. The need for investigating windfarm (as a unit) aerodynamics is thus highlighted. An actuator disk model is developed and implemented in the OpenFOAM software suite. The model is validated against 1-D momentum theory, blade element momentum theory, as well as against experimental data. The validated actuator disk model is then used to investigate an interesting microscale meteorological phenomenon called “flow convergence” caused by an array of wind turbines. This phenomenon is believed to be caused by the drop of pressure in wind farms. Wind farm numerical simulations are conducted with various approximations to investigate and explain the flow convergence phenomenon.

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Developing the Actuator Disk Model to Predict the Fluid–Structure Interaction in Numerical Simulation of Multimegawatt Wind Turbine Blades

Journal of Energy Resources Technology ◽

10.1115/1.4044576 ◽

2019 ◽

Vol 142 (3) ◽

Author(s):

Ali Behrouzifar ◽

Masoud Darbandi

Keyword(s):

Numerical Methods ◽

Wind Turbine ◽

Fluid Structure Interaction ◽

Cone Angle ◽

Disk Model ◽

Fluid Structure ◽

Aerodynamic Loads ◽

Structure Interaction ◽

Actuator Disk ◽

Analytical Approaches

Abstract The fluid–structure interaction (FSI) is generally addressed in multimegawatt wind turbine calculations. From the fluid flow perspective, the semi-analytical approaches, like actuator disk (AD) model, were commonly used in wind turbine rotor calculations. Indeed, the AD model can effectively reduce the computational cost of full-scale numerical methods. Additionally, it can substantially improve the results of pure analytical methods. Despite its great advantages, the AD model has not been developed to simulate the FSI problem in wind turbine simulations. This study first examines the effect of constant (rigid) cone angle on the performance of the chosen benchmark wind turbine. As a major contribution, this work subsequently extends the rigid AD model to nonrigid applications to suitably simulate the FSI. The new developed AD-FSI solver uses the finite-volume method to calculate the aerodynamic loads and the beam theory to predict the structural behaviors. A benchmark megawatt wind turbine is simulated to examine the accuracy of the newly developed AD-FSI solver. Next, the results of this solver are compared with the results of other researchers, who applied various analytical and numerical methods to obtain their results. The comparisons indicate that the new developed solver calculates the aerodynamic loads reliably and predicts the blade deflection very accurately.

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A Simulation Study on Risks to Wind Turbine Arrays from Thunderstorm Downbursts in Different Atmospheric Stability Conditions

Energies ◽

10.3390/en14175407 ◽

2021 ◽

Vol 14 (17) ◽

pp. 5407

Author(s):

Nan-You Lu ◽

Lance Manuel ◽

Patrick Hawbecker ◽

Sukanta Basu

Keyword(s):

Boundary Layer ◽

Wind Turbine ◽

Transition Period ◽

Atmospheric Stability ◽

Bending Moment ◽

Stability Conditions ◽

Wind Fields ◽

Worst Case ◽

Large Eddy Simulation Model ◽

Turbine Arrays

Thunderstorm downbursts have been reported to cause damage or failure to wind turbine arrays. We extend a large-eddy simulation model used in previous work to generate downburst-related inflow fields with a view toward defining correlated wind fields that all turbines in an array would experience together during a downburst. We are also interested in establishing what role contrasting atmospheric stability conditions can play on the structural demands on the turbines. This interest is because the evening transition period, when thunderstorms are most common, is also when there is generally acknowledged time-varying stability in the atmospheric boundary layer. Our results reveal that the structure of a downburst’s ring vortices and dissipation of its outflow play important roles in the separate inflow fields for turbines located at different parts of the array; these effects vary with stability. Interacting with the ambient winds, the outflow of a downburst is found to have greater impacts in an “average” sense on structural loads for turbines farther from the touchdown center in the stable cases. Worst-case analyses show that the largest extreme loads, although somewhat dependent on the specific structural load variable considered, depend on the location of the turbine and on the prevailing atmospheric stability. The results of our calculations show the highest simulated foreaft tower bending moment to be 85.4 MN-m, which occurs at a unit sited in the array farther from touchdown center of the downburst initiated in a stable boundary layer.

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Full HAWT rotor CFD simulations using different RANS turbulence models compared with actuator disk and experimental measurements

10.5194/wes-2017-6 ◽

2017 ◽

Author(s):

Nikolaos Stergiannis ◽

Jeroen van Beeck ◽

Mark C. Runacres

Keyword(s):

Experimental Data ◽

Wind Turbine ◽

Turbine Rotor ◽

Operating Conditions ◽

Experimental Measurements ◽

Horizontal Axis Wind Turbine ◽

Cfd Simulations ◽

Disk Model ◽

Actuator Disk ◽

Wind Turbine Rotor

Abstract. The development of large-scale wind energy projects has created the demand for increasingly accurate and efficient models that limit a project's uncertainties and risk. Wake effects are of great importance and are relevant for the optimization of wind farms. Despite a growing body of research, there are still many open questions and challenges to overcome. In computational modelling, there are always numerous input parameters such as material properties, geometry, boundary conditions, initial conditions, turbulence modelling etc. whose estimation is difficult and their values are often inaccurate or uncertain. Due to the lack of information of several sources, e.g., uncertainties present in operating conditions as well as in the mathematical modelling, the computational output is also uncertain. It is therefore very important to validate the mathematical models with experiments performed in controlled conditions. In the present paper, the single wake characteristics of a Horizontal-Axis Wind Turbine Rotor (HAWT) and their spatial evolution are investigated with different Computational Fluid Dynamics (CFD) modelling approaches and compared to experimental measurements. The steady state 3-D Reynolds-Averaged Navier Stokes (RANS) equations are solved in the open-source platform OpenFOAM, using different turbulence closure schemes. For the full-rotor CFD simulations, the Multiple Reference Frames (MRF) approach was used to model the rotation of the blades. For the simplified cases, an actuator disk model was used with the experimentally measured thrust (CT) and power (CP) coefficient values. The performance of each modelling approach is compared with experimental wind tunnel wake measurements from the 4th blind test organized by NOWITECH and NORCOWE in 2015. Numerical results are compared with experimental data along three horizontal lines downstream, covering all the wake regions. Wake predictions are shown to be very sensitive to the choice of the RANS turbulence model. For most cases, the ADM under-predicts the velocity deficit, except for the case of RNG k-ε which showed a superb performance in the mid and far wake. The full wind turbine rotor simulations showed good agreement to the experimental data, mainly in the near wake, amplifying the differences between the simplified models.

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Analytical model for the power–yaw sensitivity of wind turbines operating in full wake

Wind Energy Science ◽

10.5194/wes-5-427-2020 ◽

2020 ◽

Vol 5 (1) ◽

pp. 427-437 ◽

Cited By ~ 2

Author(s):

Jaime Liew ◽

Albert M. Urbán ◽

Søren Juhl Andersen

Keyword(s):

Wind Turbines ◽

Wind Farm ◽

Power Production ◽

Wake Flow ◽

High Fidelity ◽

Combined Effects ◽

Wind Farm Optimization ◽

Computational Fluid Dynamics Simulations ◽

Dynamics Simulations ◽

Blade Element

Abstract. Wind turbines are designed to align themselves with the incoming wind direction. However, turbines often experience unintentional yaw misalignment, which can significantly reduce the power production. The unintentional yaw misalignment increases for turbines operating in the wake of upstream turbines. Here, the combined effects of wakes and yaw misalignment are investigated, with a focus on the resulting reduction in power production. A model is developed, which considers the trajectory of each turbine blade element as it passes through the wake inflow in order to determine a power–yaw loss exponent. The simple model is verified using the HAWC2 aeroelastic code, where wake flow fields have been generated using both medium- and high-fidelity computational fluid dynamics simulations. It is demonstrated that the spatial variation in the incoming wind field, due to the presence of wakes, plays a significant role in the power loss due to yaw misalignment. Results show that disregarding these effects on the power–yaw loss exponent can yield a 3.5 % overestimation in the power production of a turbine misaligned by 30∘. The presented analysis and model is relevant to low-fidelity wind farm optimization tools, which aim to capture the combined effects of wakes and yaw misalignment as well as the uncertainty on power output.

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