A vortex-based tip/smearing correction for the actuator line

Forsting, Alexander Meyer; Pirrung, Georg Raimund; Ramos‐García, Néstor

doi:10.5194/wes-2018-76

Cited by 11 publications

(26 citation statements)

References 15 publications

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“…The smearing length scale is twice the grid size as recommended by Troldborg to guarantee numerical stability. The force smearing leads to overpredictions in the blade forces, which is counteracted by the correction of Meyer Forsting et al To ensure that the blade tip remain inside a single cell during one time step,

normalΔ t < 2 normalΔ x false/ false(normalΩ D false)

, with mesh spacing

normalΔ x

and rotational speed

normalΩ

.…”

Section: Methodology For Validationmentioning

confidence: 72%

A simple improvement of a tip loss model for actuator disc simulations

et al. 2020

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The loading of a wind turbine decreases towards the blade tip because of the velocities induced by the tip vortex. This tip loss effect has to be taken into account when performing actuator disc simulations, where the single blades of the turbine are not modeled. A widely used method applies a factor on the axial and tangential loading of the turbine. This factor decreases when approaching the blade tip. It has been shown that the factor should be different for the axial and tangential loading of the turbine to model the rotation of the resulting force vector at the airfoil sections caused by the induced velocity. The present article contains the derivation of a simple correction for the tangential load factor that takes this rotation into account. The correction does not need any additional curve fitting but just depends on the local airfoil characteristics and angle of attack. Actuator disc computations with the modified tip loss correction show improved agreement with results from actuator line, free wake lifting line, and blade element momentum simulations.

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normalΔ t < 2 normalΔ x false/ false(normalΩ D false)

, with mesh spacing

normalΔ x

and rotational speed

normalΩ

.…”

Section: Methodology For Validationmentioning

confidence: 72%

A simple improvement of a tip loss model for actuator disc simulations

et al. 2020

Self Cite

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“…An adequate and physical filtering may be achieved using subgrid scale models and proper account of viscous diffusion -but such models are not readily available for a filament-based vortex method and are hard to achieve unless the topology and connectivity of the wake are modified. The topic of regularization is being actively researched for actuator line CFD (Martínez-Tossas and Meneveau, 2019;Meyer Forsting et al, 2019) and vortex-based methods (Li et al, 2020). Future work should focus on the convergence of the lifting-line method with blade discretization and convergence of the filament-based vortex method, through comparisons with measurements and blade-resolved simulations.…”

Section: Discussion On Regularizationmentioning

confidence: 99%

A multipurpose lifting-line flow solver for arbitrary wind energy concepts

Branlard

Brownstein²,

Strom³

et al. 2022

Wind Energ. Sci.

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Abstract. In this work, we extend the AeroDyn module of OpenFAST to support arbitrary collections of wings, rotors, and towers. The new standalone AeroDyn driver supports arbitrary motions of the lifting surfaces and complex turbulent inflows. Aerodynamics and inflow are assembled into one module that can be readily coupled with an elastic solver. We describe the features and updates necessary for the implementation of the new AeroDyn driver. We present different case studies of the driver to illustrate its application to concepts such as multirotors, kites, or vertical-axis wind turbines. We perform verification and validation of some of the new features using the following test cases: elliptical wings, horizontal-axis wind turbines, and 2D and 3D vertical-axis wind turbines. The wind turbine simulations are compared to existing tools and field measurements. We use this opportunity to describe some limitations of current models and to highlight areas that we think should be the focus of future research in wind turbine aerodynamics.

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“…The governing equations obtained by filtering the N‐S equations are expressed as:

\frac{∂ρ}{∂t} + \frac{\partial}{\partial x_{i}} ((), normalρ {\overset{false~}{normalu}}_{i}) = 0,

\frac{\partial {\overset{false~}{normalu}}_{i}}{∂t} + \frac{\partial {\overset{false~}{normalu}}_{i} {\overset{false~}{normalu}}_{j}}{\partial x_{j}} = - \frac{1}{ρ} \frac{\partial \overset{p}{true}}{\partial x_{i}} + normalμ \frac{\partial}{\partial x_{j}} ((), \frac{\partial {\overset{u}{true}}_{normali}}{\partial {normalx}_{normali}}) + \frac{\partial {\overset{false~}{normalτ}}_{ij}}{\partial x_{j}} + f_{i},

where, ρ denotes the density,

\overset{p}{true}

is the fitted pressure,

{\overset{false~}{u}}_{i}

represents the fitted velocities (

\overset{u}{true}

\overset{v}{true}

\overset{w}{true}

), μ is the viscosity,

{\overset{false~}{τ}}_{ij}

denotes the SGS stress, and f i is the source term representing the external force because of the effects of the wind turbine, which is determined by ALM . In the present LES, the Gaussian smearing technology capable of improving the accuracy and the stability of the simulation when using ALM was not applied. But the comparison between the present numerical simulation and the experiment is good as presented below.…”

Section: Wind Turbine Wake Simulationmentioning

confidence: 99%

Numerical simulations of fatigue loads on wind turbines operating in wakes

Liu

Ishihara

et al. 2020

Wind Energy

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Wake effects increase the fatigue loads on wind turbines in operation. However, the wake flow is considerably different from the traditional boundary layer flow, and poses many challenges in determining the fatigue loads on wind turbines operating in a wake. Therefore, in the present study, the actuator-line model was adopted to numerically simulate the wake flow and an in-house code named AOWT, which is based on a generalized coordinate method, was developed for analyzing the dynamics of wind turbines under an arbitrary distribution of the turbulent flow field varying in time and space. Using the numerically modeled instantaneous wake flow fields and AOWT, the dynamic response of a wind turbine, located at specified positions in both tandem and staggered arrangements in a wake, was examined, and the fatigue loads were determined. Furthermore, to determine the major contributions to the fatigue loads, the loads induced by the spatial variation of the mean flow fields were predicted. To the best of the authors' knowledge, no such analysis has been conducted thus far. Importantly, it was found that in the near-wake region, the mean flow field had a significant influence on the fatigue loads, especially in the staggered layout. However, there is no analytical wake model available in the literature capable of predicting the near-wake mean flow fields. Therefore, in this study, a near-wake model was proposed, which yielded satisfactory predictions of the mean velocities in the near-wake region. K E Y W O R D Sblade element method, dynamic response, fatigue load, LES, wake flow, wake model | INTRODUCTIONWind turbines are usually installed as wind farms, in which the upstream wind turbines disturb the upcoming flow field and increase the downstream turbulence. 1-7 Consequently, the fatigue loads on the downstream wind turbines owing to the wake effects are different from those created by a traditional boundary layer flow. 8,9 A method using the effective turbulence intensity 10,11 has been commonly employed to assess the wake effects on the fatigue loads on wind turbines. However, the flow field in a wake is strongly distorted in terms of both the turbulence intensity and the mean flow. As a result, detailed examinations of the wake effects on the fatigue loads are needed. Whereas, the researches 12-15 considering this issue are not as many as those about the fatigue loads induced by the traditional boundary layer. [16][17][18][19][20] This could be owing to the fact that the wind turbine wake flow is much different with the traditional boundary layer flow, failing the applications of the conventional approaches for the turbulent flow generations, 11,21 posing many challenges in determining the fatigue loads on a wind turbine operating in wakes. In recent years, the engineering models, such as

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A vortex-based tip/smearing correction for the actuator line

Cited by 11 publications

References 15 publications

A simple improvement of a tip loss model for actuator disc simulations

A simple improvement of a tip loss model for actuator disc simulations

A multipurpose lifting-line flow solver for arbitrary wind energy concepts

Numerical simulations of fatigue loads on wind turbines operating in wakes

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