Evaluation and Control of Loads on Wind Turbines under Different Operating Conditions by Means of CFD

Schulz, Christoph; Fischer, Annette; Weihing, Pascal; Lutz, Thorsten; Krämer, Ewald

doi:10.1007/978-3-319-24633-8_30

Cited by 11 publications

(5 citation statements)

References 10 publications

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“…In the region close to the turbine, it is refined to a cell size of 1m. All values of the domain size and grid spacings emerged from grid convergence studies and showed reliable results in other simulations published . The boundary conditions chosen are a slip wall at the ground and far‐field conditions at all other edges.…”

Section: Numerical Realizationmentioning

confidence: 68%

CFD study on the impact of yawed inflow on loads, power and near wake of a generic wind turbine

Schulz¹,

Letzgus²,

Lutz³

et al. 2016

Wind Energy

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This article deals with the influence of yawed inflow conditions on the performance of a single generic 2.4 MW wind turbine. It presents the results of studies performed at the Institute of Aerodynamics and Gas Dynamics by means of computational fluid dynamics, using a fully meshed wind turbine with all boundary layers being resolved. The block-structured flow solver FLOWer is used; a dual-time stepping method for temporal discretization and a second-order Jameson-Schmidt-Turkel method for the calculation of the convective fluxes are applied. All simulations are carried out using a detached eddy simulation approach. In detail, two different wind speeds and a yaw angle range between 50 ı and C50 ı are evaluated in the paper. Based on these data, it is shown that the reduction of power output follows a cosine to the power of X function of the yaw angle. Furthermore, the growing azimuthal non-uniformity of the load distributions with increasing yaw angle magnitude is analysed by spanwise load distributions. As a central influence on the load distributions, the advancing and retreating blade effect is identified. Moreover, the deflection of the wake as a result of the inflow is investigated, and the deflection angles are compared with a modelling approach. A connection line between wake deflection and load asymmetry is drawn. The results are of particular importance for wind park situations with downstream turbines facing the distorted inflow created from upstream ones. 253CFD study on the impact of yawed inflow on a generic wind turbine C. Schulz et al.dynamics solvers using, among others, actuator disc approaches. Several years later, the measurements performed within the Model Experiment in Controlled Conditions (MEXICO) project enlarged the yaw database. 6 This time, a three-bladed model wind turbine was investigated, collecting data of the near wake as well as blade loads and pressure distributions. 6 Within several follow-up projects, the data have been analysed and recent publications 8,9,14 showed reasonable agreement between measurements and simulations. In detail, the simulated wake deflection was investigated and the distortion of the wake was discussed. Even though a great success, none of the measurements were able to describe all effects occurring from yaw misalignment. The reduction of power and mean loads of the turbine, the changing angle of attack over one revolution, the varying induction, the wake distortion and how the different effects correlate with each other. The NASA-Ames measurements cover a wide operational range but provide only little information about the rotor wake. MEXICO and its wide range of particle image velocimetry data provide more information about the near-wake flow field, but lacks the wide range of yaw angles and faces some limitations in turbine set-up as the rotor is not tilted and the tower far downstream the rotor compared with a full-scale turbine. 6,7 Looking at the costs, it is hardly feasible to collect all data needed to investigate most of the yaw effects and cover...

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Section: Numerical Realizationmentioning

confidence: 68%

CFD study on the impact of yawed inflow on loads, power and near wake of a generic wind turbine

Schulz¹,

Letzgus²,

Lutz³

et al. 2016

Wind Energy

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“…A CFD reference solution using the AVATAR 10 MW rotor was calculated with the process chain for simulations of wind turbines developed at the Institute of Aerodynamics and Gas Dynamics (IAG, USTUTT) in the last years (i.e., Schulz et al, 2016). The main part of the chain is the CFD code FLOWer, which is complemented by different preprocessing and post-processing tools.…”

Section: Flowermentioning

confidence: 99%

Validation and accommodation of vortex wake codes for wind turbine design load calculations

Boorsma

Wenz

Lindenburg³

et al. 2020

Wind Energ. Sci.

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Abstract. The computational effort for wind turbine design load calculations is more extreme than it is for other applications (e.g., aerospace), which necessitates the use of efficient but low-fidelity models. Traditionally the blade element momentum (BEM) method is used to resolve the rotor aerodynamic loads for this purpose, as this method is fast and robust. With the current trend of increasing rotor size, and consequently large and flexible blades, a need has risen for a more accurate prediction of rotor aerodynamics. Previous work has demonstrated large improvement potential in terms of fatigue load predictions using vortex wake models together with a manageable penalty in computational effort. The present publication has contributed towards making vortex wake models ready for application to certification load calculations. The observed reduction in flapwise blade root moment fatigue loading using vortex wake models instead of the blade element momentum (BEM) method from previous publications has been verified using computational fluid dynamics (CFD) simulations. A validation effort against a long-term field measurement campaign featuring 2.5 MW turbines has also confirmed the improved prediction of unsteady load characteristics by vortex wake models against BEM-based models in terms of fatigue loading. New light has been shed on the cause for the observed differences and several model improvements have been developed, both to reduce the computational effort of vortex wake simulations and to make BEM models more accurate. Scoping analyses for an entire fatigue load set have revealed the overall fatigue reduction may be up to 5 % for the AVATAR 10 MW rotor using a vortex wake rather than a BEM-based code.

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“…The CFD computations were performed using the process chain for wind turbine simulation of the Institute of Aerodynamics and Gas Dynamics (IAG), University of Stuttgart . The main part constitutes the CFD code FLOWer, which originates from the German Aerospace Center (DLR) .…”

Section: Cfd Simulationsmentioning

confidence: 99%

Extracting the angle of attack on rotor blades from CFD simulations

et al. 2018

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In today's wind energy research, comparisons of low‐fidelity aerodynamic models with CFD simulations are common practice. While the approach for loads with respect to the rotor‐plane coordinate system such as distributed driving force or thrust is straightforward, a comparison of aerodynamic characteristics is more challenging. The radial distributions of lift, drag, and moment coefficient depend on the local angle of attack and inflow velocity, which cannot be directly determined from the flow field. It requires the elimination of the influence of the rotor blade's bound circulation and also involves the step from a three‐dimensional flow field to quantities, which depend on the blade radius. The present investigation analyzes 4 different approaches to determine the angle of attack and inflow velocity from three‐dimensional rotor simulations. In addition to 3 existing methods, a new line average technique is presented. It eliminates the effect of bound circulation by averaging along a closed shape, which is symmetric to the quarter‐chord point. All methods are assessed in cases with successively increasing complexity. The observed discrepancies are assigned to a different consideration of trailing and shed vortices. The line average approach was found to be a valuable alternative to existing approaches especially in unsteady cases and regarding the outer or tip sections of the rotor blade.

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Evaluation and Control of Loads on Wind Turbines under Different Operating Conditions by Means of CFD

Cited by 11 publications

References 10 publications

CFD study on the impact of yawed inflow on loads, power and near wake of a generic wind turbine

CFD study on the impact of yawed inflow on loads, power and near wake of a generic wind turbine

Validation and accommodation of vortex wake codes for wind turbine design load calculations

Extracting the angle of attack on rotor blades from CFD simulations

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