A1: Effect of the number of blades and solidity on the performance of a vertical axis wind turbine
Dr. Pierre-Luc Delafin | Cranfield University | United Kingdom
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Dr. Pierre-Luc Delafin | Cranfield University | United Kingdom
Takafumi Nishino | United Kingdom
Lin Wang | United Kingdom
Athanasios Kolios | United Kingdom
Two, three and four bladed Phi-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.
A2: Scale Adaptive Simulation Model for the Darrieus Wind Turbine
Dr. Krzysztof Rogowski | Warsaw University of Technology | Poland
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Dr. Krzysztof Rogowski | Warsaw University of Technology | Poland
Martin Hansen | Poland
Ryszard Maroński | Poland
Piotr Lichota | Poland
Accurate prediction of aerodynamic loads for the Darrieus wind turbine using more or less complex aerodynamic models is still a challenge. One of the problems is the small amount of experimental data available to validate the numerical codes. The major objective of the present study is to examine the scale adaptive simulation (SAS) approach for performance analysis of a one-bladed Darrieus wind turbine working at a tip speed ratio of 5 and at a blade Reynolds number of 40 000. The three-dimensional incompressible unsteady Navier-Stokes equations are used. Numerical results of aerodynamic loads and wake velocity profiles behind the rotor are compared with experimental data taken from literature. The level of agreement between CFD and experimental results is reasonable.
A3: Forced pitch motion of wind turbines
Vladimir Leble | University of Glasgow | United Kingdom
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Vladimir Leble | University of Glasgow | United Kingdom
The possibility of a wind turbine entering vortex ring state during pitching oscillations is explored in this paper. The aerodynamic performance of the rotor was computed using the Helicopter Multi-Block flow solver. This code solves the Navier-Stokes equations in integral form using the arbitrary Lagrangian-Eulerian formulation for time-dependent domains with moving boundaries. A 10-MW wind turbine was put to perform yawing and pitching oscillations suggesting the partial vortex ring state during pitching motion. The results also show the strong effect of the frequency and amplitude of oscillations on the wind turbine performance.
A4: Comparison of two vortex models of wind turbines using a free vortex wake scheme
Dr. Bofeng Xu | Hohai University | China
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Dr. Bofeng Xu | Hohai University | China
Yue Yuan | China
Tongguang Wang | China
Zhenzhou Zhao | China
Developing suitably generalized models for rotor blade vortices that accurately predict their evolution continues to be a challenge for wind turbine analysts. During the past few decades, several vortex models have been developed according to the theoretical analysis and the experimental research. A comparison of two different vortex models is made for predicting wind turbine aerodynamic performance using a free vortex wake (FVW) model. The two models are the Lamb-Oseen vortex model for laminar vortices and the β-Vatistas model for turbulent vortices. A new formula that approximates parameter β, which represents the degree of turbulence in the β-Vatistas model, is proposed. The formula of parameter β is validated by comparison of simulated and measured aerodynamic performances of wind turbines of different blade tip vortex Reynolds numbers. Then, the induced velocity streamlines and the distribution of the axial velocity in the rotational plane are simulated. Also, the differences due to the vortex models are discussed.
A5: A numerical analysis to evaluate Betz' Law for vertical axis wind turbines
Frederik Thönnißen | RWTH Aachen University | Germany
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Authors:
Frederik Thönnißen | RWTH Aachen University | Germany
Markus Marnett | Germany
Benedikt Roidl | Germany
Wolfgang Schröder | Germany
The upper limit for the energy conversion rate of horizontal axis wind turbines (HAWT) is known as the Betz limit. Often this limit is also applied to vertical axis wind turbines (VAWT). However, a literature review reveals that early analytical approaches predicted higher values for the maximum power output of VAWTs than the Betz limit. Thus, it can be questioned whether the application of Betz's Law to VAWTs is justified. To answer this question, the presented approach combines a free vortex model with a 2D inviscid panel code to represent the flow field of a generic VAWT. To ensure the validity of the model, an active blade pitch control system is used to avoid flow separation. An optimal pitch curve avoiding flow separation is determined for one specific turbine configuration by applying an evolutionary algorithm. The analysis yields a net power output that is slightly (6%) above the Betz limit. Besides the numerical result of an increased energy conversion rate, especially the identification of two physical power increasing mechanisms shows, that the application of Betz's Law to VAWTs is not justified.
A6: Comparison of upwind and downwind operation of the NREL Phase VI Experiment
Dr. Scott Larwood | University of the Pacific | United States
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Authors:
Dr. Scott Larwood | University of the Pacific | United States
Raymond Chow | United States
Wind tunnel data are presented comparing upwind and downwind operation of the National Renewable Energy Laboratory's Phase VI wind turbine. Power was not reduced as expected with downwind operation, which may be attributed to inboard 3-D effects. Average flap bending loads were reduced with downwind coning and compared well with prediction. Blade fatigue loads were increased with downwind operation; however, fatigue was mitigated with an aerodynamic tower shroud. The shroud needs to remain aligned with the freestream, demonstrated by an increase in fatigue loads from a 10° error in alignment. Tower wake data were acquired at the rotor location with and without the shroud. The bare-tower wake data compared well with published work. The shroud wake data at 10° alignment error showed velocity reduction and turbulence approaching the bare tower values. Downwind operation, with an aligning tower shroud, should be considered for future designs given the load benefits of downwind coning.
A7: Simulation and Optimization of an Airfoil with Leading Edge Slat
Matthias Schramm | ForWind - University of Oldenburg | Germany
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Matthias Schramm | ForWind - University of Oldenburg | Germany
Bernhard Stoevesandt | Germany
Joachim Peinke | Germany
A gradient-based optimization is used in order to improve the shape of a leading edge slat upstream of a DU 91-W2-250 airfoil. The simulations are performed by solving the Reynolds-Averaged Navier-Stokes equations (RANS) using the open source CFD code OpenFOAM. Gradients are computed via the adjoint approach, which is suitable to deal with many design parameters, but keeping the computational costs low. The implementation is verified by comparing the gradients from the adjoint method with gradients obtained by finite differences for a NACA 0012 airfoil. The simulations of the leading edge slat are validated against measurements from the acoustic wind tunnel of Oldenburg University at a Reynolds number of Re = 0.6 mio. The shape of the slat is optimized using the adjoint approach resulting in a drag reduction of 2 %. Although the optimization is done for Re = 0.6 mio , the improvements also hold for a higher Reynolds number of Re = 7.9 mio, which is more realistic at modern wind turbines.
A8: The Effect of Aerodynamic Evaluators on the Multi-Objective Optimization of Flatback Airfoils
Michael Miller | Carleton University | Canada
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Authors:
Michael Miller | Carleton University | Canada
Kenny Lee Slew | Canada
Edgar Matida | Canada
Due to the long lengths of today's wind turbine rotor blades, structurally and aerodynamically efficient airfoils are required, particularly in the inboard region of the blade where structural demands are highest. Using a genetic algorithm, the multi-objective aero-structural optimization of 30% thick flatback airfoils was systematically performed for a variety of aerodynamic evaluators such as lift-to-drag ratio (CL/CD), torque (CT), and torque-to-thrust ratio (CT/CN) to determine their influence on airfoil shape and performance. The airfoil optimized for CT possessed a 4.8% thick trailing-edge, and a rather blunt leading-edge region which creates high levels of lift and correspondingly, drag. It's ability to maintain similar levels of lift and drag under forced transition conditions proved it's insensitivity to roughness. The airfoil optimized for CL/CD displayed relatively poor insensitivity to roughness due to the rather aft-located free transition points. The CT/CN optimized airfoil was found to have a very similar shape to that of the CL/CD airfoil, with a slightly more blunt leading-edge which aided in providing higher levels of lift and moderate insensitivity to roughness. The influence of the chosen aerodynamic evaluator under the specified conditions and constraints in the optimization of wind turbine airfoils is shown to have a direct impact on the airfoil shape and performance.
A9: Validation of engineering dynamic inflow models by experimental and numerical approaches
Daniel Baldacchino | Delft University of Technology | Netherlands
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Daniel Baldacchino | Delft University of Technology | Netherlands
Vincent Hong | Netherlands
Carlos Ferreira | Netherlands
G.A.M. van Kuik | Netherlands
Wei Yu | Netherlands
The state of the art engineering dynamic in ow models of Pitt-Peters, ye and ECN have been used to correct Blade Element Momentum theory for unsteady load prediction of a wind turbine for two decades. However, their accuracy is unknown. This paper is to benchmark the performance of these engineering models by experimental and numerical methods. The experimental load and ow measurements of an unsteady actuator disc were performed in the Open Jet Facility at Delft University of Technology. The unsteady load was generated by a ramp-type variation of porosity of the disc. A Reynolds Averaged Navier-Stokes (RANS) model, a Free Wake Vortex Ring (FWVR) model and a Vortex Tube Model (VTM) simulate the same transient load changes. The velocity eld obtained from the experimental and numerical methods are compared with the engineering dynamic in ow models. Velocity comparison aft the disc between the experimental and numerical methods shows the numerical models of RANS and FWVR model are capable to predict the velocity transient behaviour during transient disc loading. Velocity comparison at the disc between the engineering models and the numerical methods further shows that the engineering models predict much faster velocity decay, which implies the need for more advanced or better tuned dynamic in ow models.
A10: Simulations of wind turbine rotor with vortex generators
Dr. Niels Troldborg | Technical University of Denmark | Denmark
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Dr. Niels Troldborg | Technical University of Denmark | Denmark
Frederik Zahle | Denmark
Niels Sørensen | Denmark
This work presents simulations of the DTU 10MW wind turbine rotor equipped with vortex generators (VGs) on the inner part of the blades. The objective is to study the influence of different VG configurations on rotor performance and in particular to investigate the radial dependence of VGs, i.e. how VGs at one section of the blade may affect the aerodynamic characteristics at other radial positions. Furthermore, the performance of different sections on the blade is compared to their corresponding performance in 2D flow.
A11: Investigations of the inflow turbulence effect on rotational augmentation by means of CFD
Galih Bangga | University of Stuttgart | Germany
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Galih Bangga | University of Stuttgart | Germany
Yusik Kim | Germany
Thorsten Lutz | Germany
Pascal Weihing | Germany
Ewald Krämer | Germany
The present studies are addressed to gain more insights into the inflow turbulence effect on rotational augmentation using computational fluid dynamics. Three different cases were simulated and analysed focusing on the three-dimensional effects in the inboard blade region of a 10 MW generic wind turbine rotor. The evidence of rotational augmentation was presented and compared to two-dimensional simulations of the blade sections at consistent inflow conditions. Inflow turbulence has a very strong impact on the instantaneous blade loads and standard deviations, but the effect on the mean values is small. The amplitudes of the blade load fluctuations are amplified under turbulent inflow conditions and these are related to the blade passing frequency and the specified turbulence length scale at the inlet. Detailed examinations of these phenomena were performed and are presented in the present manuscript.
A12: LES tests on airfoil trailing edge serration
Dr. Wei Jun Zhu | Yangzhou University | China
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Authors:
Dr. Wei Jun Zhu | Yangzhou University | China
Wen Zhong Shen | China
In the present study, a large number of acoustic simulations are carried out for a low noise airfoil with different Trailing Edge Serrations (TES). The Ffowcs Williams-Hawkings (FWH) acoustic analogy is used for noise prediction at trailing edge. The acoustic solver is running on the platform of our in-house incompressible flow solver EllipSys3D. The flow solution is first obtained from the Large Eddy Simulation (LES), the acoustic part is then carried out based on the the instantaneous hydrodynamic pressure and velocity field. To obtain the time history data of sound pressure, the flow quantities are integrated around the airfoil surface through the FWH approach. For all the simulations, the chord based Reynolds number is around 1.5x106. In the test matrix, the effects from angle of attack, the TE flap angle, the length/width of the TES are investigated. Even though the airfoil under investigation is already optimized for low noise emission, most numerical simulations and wind tunnel experiments show that the noise level is further decreased by adding the TES device.
A13: Validation and comparison of aerodynamic modelling approaches for floating offshore wind turbines
Dr. Frédéric Blondel | IFPEN | France
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Authors:
Dr. Frédéric Blondel | IFPEN | France
Ronan Boisard | France
Malika Milekovic | France
Gilles Ferrer | France
David Teixeira | France
Caroline Lienard | France
The development of large capacity Floating Offshore Wind Turbines (FOWT) is an interdisciplinary challenge for the design solvers, requiring accurate modelling of both hydrodynamics, elasticity, servodynamics and aerodynamics all together. Floating platforms will induce low-frequency unsteadiness, and for large capacity turbines, the blade induced vibrations will lead to high-frequency unsteadiness. While yawed inflow conditions are still a challenge for commonly used aerodynamic methods such as the Blade Element Momentum method (BEM), the new sources of unsteadiness involved by large turbine scales and oater motions have to be tackled accurately, keeping the computational cost small enough to be compatible with design and certification purposes. In the light of this, this paper will focus on the comparison of three aerodynamic solvers based on BEM and vortex methods, on standard, yawed and unsteady inflow conditions. We will focus here on up-to-date wind tunnel experiments, such as the Unsteady Aerodynamics Experiment (UAE) database and the MexNext international project.
A14: Effects of finite aspect ratio on wind turbine airfoil measurements
Janik Kiefer | Princeton University | United States
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Authors:
Janik Kiefer | Princeton University | United States
Mark Miller | United States
Marcus Hultmark | United States
Martin Hansen | United States
Wind turbines partly operate in stalled conditions within their operational cycle. To simulate these conditions, it is also necessary to acquire 2-D airfoil data in terms of lift and drag coefficients at high angles of attack. Such data has been obtained previously, but often at low aspect ratios and only barely past the stall point, where strong wall boundary layer influence is expected. In this study, the influence of the aspect ratio on 2D airfoil data, especially in the post stall domain, is investigated. Here, a wind turbine airfoil is tested at different angles of attack and with two aspect ratios of AR = 1 and AR = 2. The tests are conducted in a wind tunnel that is pressurized up to 150 bar in order to achieve a constant Reynolds number of Re_c = 3*10^6, despite the variable chord length.
A15: Thick root airfoil design for the 10MW INNWIND.EU wind turbine
Dr. Xabier Munduate | CENER | Spain
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Authors:
Dr. Xabier Munduate | CENER | Spain
Beatriz Méndez | Spain
Arturo Muñoz | Spain
The main objective of the INNWIND.EU project is to investigate and demonstrate innovative designs for 10-20MW o shore wind turbines and their key components, such as lightweight rotors. In this context, the present paper describes the development of two new airfoils for the blade root region. From the structural point of view, the root is the region in charge of transmitting all the loads of the blade to the hub. Thus, it is very important to include airfoils with adequate structural properties in this region. The present article makes use of high-thickness and blunt trailing edge airfoils to improve the structural characteristics of the airfoils used to build this blade region. CENER's (National Renewable Energy Center of Spain) airfoil design tool uses the airfoil software XFOIL to compute the aerodynamic characteristics of the designed airfoils. That software is based on panel methods which show some problems with the calculation of airfoils with thickness bigger than 35% and with blunt trailing edge. This drawback has been overcome with the development of an empirical correction for XFOIL lift and drag prediction based on airfoil experiments. From the aerodynamic point of view, thick airfoils are known to be very sensitive to surface contamination or turbulent in ow conditions. Consequently, the design optimization takes into account the aerodynamic torque in both clean and contaminated conditions. Two airfoils have been designed aiming to improve the structural and the aerodynamic behaviour of the blade in clean and contaminated conditions. This improvement has been corroborated with Blade Element Momentum (BEM) computations.
A16: Aerodynamic analysis of clustered, diffuser-augmented wind turbines
Uli Goeltenbott | Kyushu University | Japan
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Authors:
Uli Goeltenbott | Kyushu University | Japan
Yuji Ohya | Japan
Shigeo Yoshida | Japan
Peter Jamieson | Japan
Up-scaling of wind turbines has been a major trend in order to reduce the cost of energy generation from the wind. Recent studies however show that for a given technology, the cost always rises with upscaling, notably due to the increased mass of the system. To reach capacities beyond 10 MW, multi-rotor systems (MRS) have promising advantages. On the other hand, diffuser augmented wind turbines (DAWTs) can significantly increase the performance of the rotor. Up to now, diffuser augmentation has only been applied to single small wind turbines. In the present research, DAWTs are used in a multi-rotor system. In wind tunnel experiments, the aerodynamics of two and three DAWTs, spaced in close vicinity in the same plane normal to a uniform flow, have been analysed. Power increases of up to 5% and 9% for the two and three rotor configurations are respectively achieved in comparison to a stand-alone turbine. The physical dynamics of the flows are analysed on the basis of the results obtained with a stand-alone turbine.
A17: Predictions of the cycle-to-cycle aerodynamic loads on a yawed wind turbine blade under stalled conditions using a 3D empirical stochastic model
Prof. Tonio Sant | University of Malta | Malta
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Authors:
Prof. Tonio Sant | University of Malta | Malta
Moutaz Elgammi | Malta
This paper investigates a new approach to model the cycle-to-cycle variations in the aerodynamic loads on yawed wind turbines experienced at high angles of attack. The method applies a 3D empirical stochastic model with the one-dimensional Langevin equation with the known mean values for the lift and drag data. The present analysis is based on the NREL Phase VI rotor in which the mean values for the lift and drag are derived from the pressure measurements on the blade in conjunction with a free-wake vortex model. The standard deviations of the lift and drag for the model are also required which can be determined either from measurements or numerically using CFD code. The model is an important step towards verification of several assumptions characterized as the estimated standard deviation, Gaussian white noise of the data and the estimated drift and diffusion coefficients of the Langevin equation. The results using the proposed assumptions lead to a good agreement with measurements over a wide range of operating conditions, providing motivation to implement a fully independent theoretical stochastic model for wind turbines in which the mean lift and drag force coefficients can be estimated using a dynamic stall model with a free wake vortex (FWV) model/ blade element momentum (BEM) model.
A18: Application of the lifting line vortex wake method to dynamic load case simulations
Dr. Koen Boorsma | ECN | Netherlands
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Authors:
Dr. Koen Boorsma | ECN | Netherlands
L.M. Orsi | Netherlands
M. Hartvelt | Netherlands
Within the EU AVATAR project, the added benefit of using the vortex line method is researched by calculating aero-elastic response for a variety of IEC load cases. A comparison is made to BEM to identify differences. Results are presented for yawed flow, extreme transient shear, half wake and turbulent inflow conditions. In addition to that also a dynamic pitch step case is performed including a comparison to experimental data. The aerodynamic code used for this purpose allows to easily switch between BEM and vortex line models whilst keeping the external input the same. The comparison indicates that taking into account the wake geometry yields a different aero-elastic response than BEM and often acts as a damper to fluctuations. As such estimated fatigue loads are reduced for selected load cases. Since the free vortex wake simulations come at a substantial increase of CPU-time, a hybrid approach prescribing the far wake is shown to offer a promising compromise.
A19: The influence of a cubic building on a roof mounted wind turbine
Dr. Daniel Micallef | University of Malta | Malta
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Authors:
Dr. Daniel Micallef | University of Malta | Malta
Tonio Sant | Malta
Carlos Simao Ferreira | Malta
The performance of a wind turbine located above a cubic building is not well understood. This issue is of fundamental importance for the design of small scale wind turbines. One variable which is of particular importance in this respect is the turbine height above roof level. In this work, the power performance of a small wind turbine is assessed as a function of the height above the roof of a generic cubic building. A 3D Computational Fluid Dynamics model of a 10m x 10m x 10m building is used with the turbine modelled as an actuator disc. Results have shown an improvement in the average power coefficient even in cases where the rotor is partially located within the roof separation zone. This goes against current notions of small wind turbine power production. This study can be of particular importance to guide the turbine installation height on building roof tops.
A20: Numerical and experimental investigation of an airfoil with load control in the wake of an active grid
Annette Fischer | Universität Stuttgart | Germany
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Authors:
Annette Fischer | Universität Stuttgart | Germany
Thorsten Lutz | Germany
Ewald Krämer | Germany
Ulrike Cordes | Germany
Klaus Hufnagel | Germany
Cameron Tropea | Germany
Gerrit Kampers | Germany
Michael Hölling | Germany
Joachim Peinke | Germany
A new passive load reduction system, using coupled leading and trailing edge flaps, was developed at TU Darmstadt and investigated experimentally and numerically. The experiments were performed in the wind tunnel of the University of Oldenburg, where sinusoidal inflow conditions, representing for example the tower blockage effect, were created by means of an active grid. The numerical investigations were performed at the University of Stuttgart, using a quasi two-dimensional setup and a block structured CFD solver. In the present paper, a brief description of the experimental setup is given, whereas the numerical setup, in particular the realisation of the wind tunnel conditions, is presented in more detail. Moreover, a comparison between the measured and simulated loads for an airfoil with and without adaptive camber concept is discussed.
A21: Extended Glauert Tip Correction to Include Vortex Rollup Effects
Dr. Sven Schmitz | The Pennsylvania State University | United States
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Authors:
Dr. Sven Schmitz | The Pennsylvania State University | United States
David Maniaci | United States
Wind turbine loads predictions by blade-element momentum theory using the standard tip-loss correction have been shown to over-predict loading near the blade tip in comparison to experimental data. This over-prediction is theorized to be due to the assumption of light rotor loading, inherent in the standard tip-loss correction model of Glauert. A higher-order free-wake method is used to compute the rollup process of the trailing vortex sheets downstream of wind turbine blades. Results obtained serve an exact correction function to the Glauert tip correction used in blade-element momentum methods. It is found that accounting for tip vortex rollup within the Glauert tip correction indeed results in improved prediction of turbine blade tip loads computed by blade-element momentum methods.
A22: Aeroacoustic calculations of a full scale Nordtank 500kW wind turbine
Harald Debertshaeuser | Technical University of Denmark | Denmark
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Authors:
Harald Debertshaeuser | Technical University of Denmark | Denmark
Wen Zhong Shen | Denmark
Wei Jun Zhu | Denmark
The Actuator Line/ Navier-stokes technique is used to compute the incompressible flow around a full scale Nordtank 500kW wind turbine under different complex flow conditions such as atmospheric turbulence and wind shear. The flow field is used as an input to aeroacoustic calculations based on; a semi empirical noise model; and a Navier-Stokes based computational aeroacoustic code (CAA). The Navier-Stokes based approach is solving acoustic perturbation equations and is capable of taking propagation and ground effects into account, but is limited to low frequency noise due to feasible mesh resolution, and due to the simplification in the actuator line method using body forces to represent the blade. Noise levels are compared to field measurements of a Nordtank 500kW wind turbine at different wind speeds and inflow profiles.
A23: Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines
Victor Mendoza | Uppsala University | Sweden
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Authors:
Victor Mendoza | Uppsala University | Sweden
Anders Goude | Sweden
Peter Bachant | Sweden
Martin Wosnik | Sweden
Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier--Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.
A24: Investigation of wavy blade section
Dr. Martin O. L. Hansen | DTU | Denmark
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Authors:
Dr. Martin O. L. Hansen | DTU | Denmark
Cecilia M Kobæk | Denmark
A thorough literature study of the Wave blade concept is presented. Further, is shown some CFD computations on two different geometries based on the S809 airfoil.
A25: CFD computations of the second round of MEXICO rotor measurements
Prof. Niels Nørmark Sørensen | Technical University of Denmark | Denmark
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Authors:
Prof. Niels Nørmark Sørensen | Technical University of Denmark | Denmark
Frederik Zahle | Denmark
Koen Boorsma | Denmark
Gerard Schepers | Denmark
A comparison, between selected wind tunnel data from the NEW MEXICO measuring campaign and CFD computations are shown. The present work, documents that a state of the art CFD code, including a laminar turbulent transition model, can provide good agreement with experimental data. Good agreement is shown for the integral loads, radial distributions of blades forces, pressure distributions, and the velocity profiles up- and down-stream of the rotor.
A26: CFD simulations on a rotor operating in pitch fault conditions and comparison with experiments
Dr. Luca Oggiano | IFE | Norway
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Authors:
Dr. Luca Oggiano | IFE | Norway
Koen Boorsma | Norway
Menno Kloosterman | Norway
The present paper aims to simulate and reproduce the experiments on a imbalanced rotor with one blade off pitched by 20degees carried out within the IEA task 29 Mexnext Phase III. Models of increasing complexity were used (Blade Element Method simulation (BEM) lifting line with free vortex wake (FVW) and URANS CFD) and the results were compared. The rotor has a diameter of 4.5m and three different load cases corresponding to a tip speed ratio of 5.24, 7.6 and11.2 were chosen from the test matrix performed during the experiments. The rotor speed was kept constant at 324.9RPM. BEM and FVW simulations were performed using the Aero Module tool developed by ECN that offers both an advanced BEM formulation and a FVW formulation named AWSM. The commercial solver STARCCM+ was for the CFD simulations and an Unsteady RANS approach with the k-ω SST turbulence model was chosen. Loads recorded with strain gauges during the experiments and pressures on the equipped blades were compared with results from the numerical simulations. The comparison provided good agreement in the low tip speed ratio cases while differences were more noticeable for the highest tip speed ration load case.
A27: Benchmarking aerodynamic prediction of unsteady rotor aerodynamics of active flaps on wind turbine blades using ranging fidelity tools
Dr. Athanasios Barlas | DTU | Denmark
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Authors:
Dr. Athanasios Barlas | DTU | Denmark
Eva Jost | Denmark
Georg Pirrung | Denmark
Theofanis Tsiantas | Denmark
Vasilis Riziotis | Denmark
Sachin Navalkar | Denmark
Thorsten Lutz | Denmark
Jan-Willem van Wingerden | Denmark
Simulations of a stiff rotor configuration of the DTU 10MW Reference Wind Turbine are performed in order to assess the impact of prescribed flap motion on the aerodynamic loads on a blade sectional and rotor integral level. Results of the engineering models used by DTU (HAWC2), TUDelft (Bladed) and NTUA (hGAST) are compared to the CFD predictions of USTUTT-IAG (FLOWer). Results show fairly good comparison in terms of axial loading, while alignment of tangential and drag-related forces across the numerical codes needs to be improved, together with unsteady corrections associated with rotor wake dynamics. The use of a new wake model in HAWC2 shows considerable accuracy improvements.
A28: Jet flow control at the blade scale to alleviate loads
Dr. Caroline Braud | LHEEA laboratory | France
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Authors:
Dr. Caroline Braud | LHEEA laboratory | France
Emmanuel Guilmineau | France
The turbulent atmospheric boundary layer in which wind turbines are implemented is strongly inhomogeneous and unsteady. This induces unsteady mechanical loads at different characteristic time scales from seconds to minutes which limits significantly their life time. The present work focuses on the flow control strategies at the blade scale, to manipulate lift and thus alleviate fatigue loads. The design of a NACA65-4-421 airfoil profile has been modified to be able to implement jet control. Slotted jet and discrete jet configurations were implemented numerically and experimentally respectively. Results show the ability of both configurations to increase the lift by up to 30% using a significicant redistribution of the mean shear. Efficiency seems to be more important using slotted jets, which however needs to be confirmed from 3D simulations.
A29: Analysis of high Reynolds numbers effects on a wind turbine airfoil using 2D wind tunnel test data
Dr. Xabier Munduate | CENER | Spain
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Authors:
Dr. Xabier Munduate | CENER | Spain
Oscar Pires | Spain
Ozlem Ceyhan | Spain
Markus Jacobs | Spain
Herman Snel | Spain
The aerodynamic behaviour of a wind turbine airfoil has been measured in a dedicated 2D wind tunnel test at DNW High Pressure Wind Tunnel in Gottingen (HDG), Germany. The tests have been performed on the DU00W212 airfoil at different Reynolds numbers: 3, 6, 9, 12 and 15 million, and at low Mach numbers (below 0.1). Both clean and tripped conditions of the airfoil have been measured. An analysis of the impact of a wide Reynolds number variation over the aerodynamic characteristics of this airfoil has been performed
A30: Discontinuous Galerkin methodology for Large-Eddy Simulations of wind turbine airfoils
Ariane Frère | Cenaero - Université catholique de Louvain | Belgium
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Authors:
Ariane Frère | Cenaero - Université catholique de Louvain | Belgium
Niels N. Sørensen | Belgium
Koen Hillewaert | Belgium
Philippe Chatelain | Belgium
Grégoire Winckelmans | Belgium
This paper aims at evaluating the potential of the Discontinuous Galerkin (DG) methodology for Large-Eddy Simulation (LES) of wind turbine airfoils. The DG method has shown high accuracy, excellent scalability and capacity to handle unstructured meshes. It is however not used in the wind energy sector yet. This present work studies blade section aerodynamics at low and large Reynolds numbers (Re) on the Eppler 387 and the NACA4412 airfoils. As wall-resolved LES is still unaffordable at high Re, a wall-modeled LES (WMLES) approach is used. Both LES and WMLES are compared to experiments as well as state-of-the-art models, namely XFOIL and Reynolds Averaged Navier-Stokes (RANS). At low Re, the LES agree slightly better with the experiment than both XFOIL and RANS. At high Re, although the wall-model approach used is very basic, all three methods provide equivalent accuracy. The present work is hence considered as a strong step forward in the use of LES at high Reynolds numbers.
A31: Effect of Wavy Trailing Edge on 100-meter Flatback Wind Turbine Blade
Seung Joon Yang | University of Maryland | United States
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Authors:
Seung Joon Yang | University of Maryland | United States
Prof. James D Baeder | University of Maryland | Germany
The flatback trailing edge design for modern 100meter wind turbine blade has been developed and proposed to make wind turbine blade to be slender and lighter. On the other hand, it will increase aerodynamic drag; consequently the increased drag diminishes turbine power generation. Thus, an aerodynamic drag reducing technique should be accompanied with the flatback trailing edge in order to prevent loss of turbine power generation. In this work, a drag mitigation design, span-wise wavy trailing edge blade, has been applied to a modern 100meter blade. The span-wise trailing edge acts as a vortex generator, and breaks up the strong span-wise coherent trailing edge vortex structure at the flatback airfoil trailing edge which is a major source of large drag. Three-dimensional unsteady Computational Fluid Dynamics (CFD) simulations have been performed for sections of real scale wind turbine blade geometries. Delayed Detached Eddy Simulation (DDES) with the modified laminar-turbulent transition model has been applied to obtain accurate flow field predictions. Graphical Processor Unit (GPU)-accelerated computation has been conducted to reduce computational costs of the real scale wind turbine blade simulations. To verify the structural reliability of the wavy modification of the blade a simple Eigen buckling analysis has been performed in the current study.
A32: On the influence of airfoil deviations on the aerodynamic performance of wind turbine rotors
Jan Winstroth | ForWind - Institute of Turbomachinery and Fluid Dynamics | Germany
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Authors:
Jan Winstroth | ForWind - Institute of Turbomachinery and Fluid Dynamics | Germany
Joerg R. Seume | Germany
The manufacture of large wind turbine rotor blades is a difficult task. Due to the complexity, airfoil deviations between the design airfoils and the manufactured blade are certain to arise. Presently, the understanding of the impact of manufacturing uncertainties on the aerodynamic performance is still incomplete. The present work analyzes the influence of a series of airfoil deviations likely to occur by means of CFD and FAST. The average power production of the NREL 5MW wind turbine is used to evaluate the different airfoil deviations. The most severe influences are observed for mold tilt towards the leading and thick bond lines. By applying the cantilever correction, the influence of thick bond lines is almost compensated. Airfoil waviness is very dependent on amplitude height and the location along the surface of the airfoil. Increased influence is observed for backward facing steps, once they are high enough to trigger boundary layer transition close to the leading edge.
A33: On the aero-elastic design of the DTU 10MW wind turbine blade for the LIFES50+ wind tunnel scale model
Dr. Luca Bernini | POLITECNICO DI MILANO | Italy
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Authors:
Dr. Luca Bernini | POLITECNICO DI MILANO | Italy
Ilmas Bayati | Italy
Marco Belloli | Italy
Luca Bernini | Italy
Robert Mikkelsen | Italy
Alberto Zasso | Italy
This paper illustrates the aero-elastic optimal design, the realization and the veri cation of the wind tunnel scale model blades for the DTU 10 MW wind turbine model, within LIFES50+ project. The aerodynamic design was focused on the minimization of the di erence, in terms of thrust coe cient, with respect to the full scale reference. From the Selig low Reynolds database airfoils, the SD7032 was chosen for this purpose and a proper constant section wing was tested at DTU red wind tunnel, providing force and distributed pressure coe cients for the design, in the Reynolds range 30-250 E3 and for di erent angles of attack. The aero-elastic design algorithm was set to de ne the optimal spanwise thickness over chord ratio (t/c), the chord length and the twist to match the rst apwise scaled natural frequency. An aluminium mould for the carbon bre was CNC manufactured based on B-Splines CAD de nition of the external geometry. Then the wind tunnel tests at Politecnico di Milano con rmed successful design and manufacturing approaches.
A34: Noise model for serrated trailing edges compared to wind tunnel measurements
Prof. Wen Zhong Shen | Technical University of Denmark | Denmark
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Authors:
Prof. Wen Zhong Shen | Technical University of Denmark | Denmark
Frank Bertagnolio | Denmark
Jesper Madsen | Denmark
Andreas Fischer | Denmark
A new CFD RANS based method to predict the far field sound pressure emitted from an aerofoil with serrated trailing edge has been developed. The model was validated by comparison to measurements conducted in the Virginia Tech Stability Wind Tunnel. The model predicted 3 dB lower sound pressure levels, but the tendencies for the different configurations were predicted correctly. Therefore the model can be used to optimise the serration geometry. A disadvantage of the new model is that the computational costs are significantly higher than for the Amiet model for a straight trailing edge. However, it is by decades faster than LES methods.
A35: Fluid-structure coupled computations of the NREL 5MW wind turbine blade during standstill
Bastian Dose | ForWind - University of Oldenburg | Germany
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Authors:
Bastian Dose | ForWind - University of Oldenburg | Germany
Hamid Rahimi | Germany
Iván Herráez | Germany
Joachim Peinke | Germany
Bernhard Stoevesandt | Germany
This work is aimed at investigating the aero-elastic behavior of a wind turbine blade subjected to strong wind speeds during standstill. This type of investigation still remains a challenge for most wind turbine simulation codes. For this purpose, a new developed high fidelity framework for fluid-structure coupled computations of wind turbines is presented and numerical simulations are conducted on the NREL 5MW reference wind turbine. The framework couples the open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM with an in-house beam solver, based on the Geometrically Exact Beam Theory (GEBT). The obtained results are compared to the aero-elastic tool FAST, which can be considered as a state-of-the-art wind turbine simulation code. The evaluation of the fluid-structure coupled CFD simulations reveals clear differences in the results compared to FAST. While the mean deflections show a reasonable agreement, the dynamics of the edgewise deflections differ significantly.
A36: Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays
Daniel Baldacchino | Delft University of Technology | Netherlands
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Authors:
Daniel Baldacchino | Delft University of Technology | Netherlands
Daniele Ragni | Netherlands
Carlos Ferreira | Netherlands
Gerard van Bussel | Netherlands
In this work, we present a simple point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the infinite vortex cascade, a compound numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, without imposing the constraint of equal vortex strength. By parametrising the resulting system of equations using the vortex strength ratio and the vortex row separation, the qualitative features of the ensuing motion are mapped. A translating and an orbiting regime are identified for different cascade separations. The latter regime occurs for all unequal strength vortex pairs. Thus, the motion is further classified by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are sufficiently large such as to appear, in the short term, as translational, or linear. However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential flow model show qualitative agreement and the presence of viscous effects account for the major discrepancies. Despite this, the model appears to capture the orbital mode observed in the measurements.
A37: Wind Turbine Blade Design for Subscale Testing
Prof. Jonathan Naughton | University of Wyoming | United States
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Authors:
Prof. Jonathan Naughton | University of Wyoming | United States
Arash Hassanzadeh | United States
Chris Kelley | United States
David Maniaci | United States
Two different inverse design approaches are proposed for developing wind turbine blades for sub-scale wake testing. In the first approach, dimensionless circulation is matched for full scale and sub-scale wind turbine blades for equal shed vorticity in the wake. In the second approach, the normalized normal and tangential force distributions are matched for large scale and small scale wind turbine blades, as these forces determine the wake dynamics and stability. The two approaches are applied for the same target full scale turbine blade, and the shape of the blades are compared. The results show that the two approaches have been successfully implemented, and the designed blades are able to produce the target circulation and target normal and tangential force distributions.
A39: What is the critical height of leading edge roughness for aerodynamics?
Christian Bak | DTU Wind Energy | Denmark
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Authors:
Christian Bak | DTU Wind Energy | Denmark
Mac Gaunaa | Denmark
Anders Olsen | Denmark
Niels Sørensen | Denmark
Emil Olsen | Denmark
In this paper the critical leading edge roughness height is analyzed in two cases: 1) leading edge roughness influencing the lift-drag ratio and 2) leading edge roughness influencing the maximum lift. The analysis was based on wind tunnel measurements on the airfoils NACA0015, Risoe-B1-18 and Risoe-C2-18 and at three different Reynolds numbers with two different leading edge roughness tape heights. First, an analysis of the momentum thickness as function of Reynolds number was carried out based on the boundary layer theory by Thwaites. Secondly, the wind tunnel measurements combined with panel code predictions of the boundary layer momentum thickness created the basis for determining the impact of roughness on the aerodynamic performance. The critical heights were related to the Reynolds numbers and thereby the size of the wind turbines.
A40: Numerical Study of Aerodynamic Characteristics of a Symmetric NACA Section with Simulated Ice Shapes
Narges Tabatabaei | Luleå tekniska universitet | Sweden
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Authors:
Narges Tabatabaei | Luleå tekniska universitet | Sweden
Michel Cervantes | Sweden
Chirag Trivedi | Sweden
Jan-Olov Aidanpaa | Sweden
To develop a numerical model of icing on wind turbine blades, a CFD simulation was conducted to investigate the effect of critical ice accretions on the aerodynamic characteristics of a 0.610 m chord NACA 0011 airfoil section. Aerodynamic performance coefficients and pressure profile were calculated and compared with the available measurements for a chord Reynolds number of 1.83×106. Ice shapes were simulated with flat plates (spoiler-ice) extending along the span of the wing. Lift, drag, and pressure coefficients were calculated in zero angle of attack through the steady state and transient simulations. Different approaches of numerical studies have been applied to investigate the icing conditions on the blades. The simulated separated flow over the sharp spoilers is challenging and can be seen as a worst test case for validation. It allows determining a reliable strategy to simulate real ice shapes for which the detailed validation cannot easily be provided.
C1: Large Wind Turbine Rotor Design using an Aero-Elastic / Free-Wake Panel Coupling Code
Matias Sessarego | Technical University of Denmark | Denmark
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Authors:
Matias Sessarego | Technical University of Denmark | Denmark
Nestor Ramos-Garcia | Denmark
Wen Zhong Shen | Denmark
Jens Norkaer Sorensen | Denmark
Despite the advances in computing resources in the recent years, the majority of large wind-turbine rotor design problems still rely on aero-elastic codes that use blade element momentum (BEM) approaches to model the rotor aerodynamics. The present work describes an approach to wind-turbine rotor design by incorporating a higher-fidelity free-wake panel aero-elastic coupling code called MIRAS-FLEX. The optimization procedure includes a series of design load cases and a simple structural design code. Due to the heavy MIRAS-FLEX computations, a surrogate-modeling approach is applied to mitigate the overall computational cost of the optimization. Improvements in cost of energy, annual energy production, maximum flap-wise root bending moment, and blade mass were obtained for the NREL 5MW baseline wind turbine.
C2: Reduction of fatigue loads on jacket substructure through blade design optimization for multi-megawatt wind turbines at 50 m water depths
Wilfried Njomo Wandji | Technical University of Denmark | Denmark
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Authors:
Wilfried Njomo Wandji | Technical University of Denmark | Denmark
Christian Pavese | Denmark
Anand Natarajan | Denmark
Frederik Zahle | Denmark
This paper addresses the reduction of the fore-aft damage equivalent moment at the tower base for multi-megawatt offshore wind turbines mounted on jacket type substructures at 50 m water depths. The study investigates blade design optimization of a reference 10 MW wind turbine under standard wind conditions of onshore sites. The blade geometry and structure is optimized to yield a design that minimizes tower base fatigue loads without significant loss of power production compared to that of the reference setup. The resulting blade design is then mounted on a turbine supported by a jacket and placed under specific offshore site conditions. The new design achieves alleviate fatigue damage equivalent loads also in the jacket members, showing the possibility to prolong its design lifetime or to save material in comparison to the reference jacket. Finally, the results suggest additional benefit on the efficient design of other components such as the constituents of the nacelle.
C3: Aeroelastic measurements and simulations of a small wind turbine operating in the built environment
Samuel Evans | The University of Newcastle, Australia | Australia
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Authors:
Samuel Evans | The University of Newcastle, Australia | Australia
David Bradney | Australia
Philip Clausen | Australia
Small wind turbines, when compared to large commercial scale wind turbines, often lag behind with respect to research investment, technological development, and experimental verification of design standards. In this study we assess the simplified load method (SLM) outlined in IEC 61400.2 for use in determining fatigue loading of small wind turbine blades. We compare these calculated loads to fatigue damage cycles from both measured in-service operation, and aeroelastic modelling of a small 5 kW Aerogenesis wind turbine. Damage cycle ranges and corresponding stress ratios show good agreement when comparing both aeroelastic simulations and operational measurements. Loads calculated via SLM were shown to significantly overpredict load ranges while underpredicting the occurrence of damage cycles by 89%. Due to the difficulty in measuring and acquiring operational loading, we recommend the use of aeroelastic modelling as a method of mitigating the over-conservative SLM for fatigue loading.
C4: A method to find the 50-year extreme load during production
René Bos | Delft University of Technology | Netherlands
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Authors:
René Bos | Delft University of Technology | Netherlands
Dick Veldkamp | Netherlands
An important yet difficult task in the design of wind turbines is to assess the extreme load behaviour, most notably finding the 50-year load. Where existing methods often focus on ways to extrapolate from small sample sizes, this paper proposes a different approach. It combines generating constrained gusts in turbulence fields, Delaunay tessellation to assign probabilities and a genetic algorithm to find the desired load in an efficient way. The individual parts of the method are verified and the results are compared to both crude Monte Carlo and importance sampling. We found that using a genetic algorithm is a promising approach to find the 50-year load, with only a small number of load cases (~103) to be evaluated and requiring no user input but an appropriate fitness function.
C5: Stall-Induced Vibrations of the AVATAR Rotor Blade
Dr. Martin Stettner | GE Global Research Europe | Germany
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Authors:
Dr. Martin Stettner | GE Global Research Europe | Germany
Marianne Jacoba Reijerkerk | Germany
Alexander Lünenschloß | Germany
Vasilis Riziotis | Germany
Alessandro Croce | Germany
Luca Sartori | Germany
Riccardo Riva | Germany
Johan M. Peeringa | Germany
In the course of the AVATAR project, partner predictions for key load components in storm/idle conditions separated in two groups. One group showed large loading due to edgewise instability, the other group damped edgewise oscillation and lower load levels. To identify the cause for this separation, the impact of structural and aerodynamic modeling options on damping of stall-induced vibrations is investigated for two simplified operating conditions of a single AVATAR blade. The choice of the dynamic stall model is found to be the primary driver, and is therefore most likely also the reason for previously observed differences in AVATAR storm load predictions. Differences in structural dynamics, mode shapes, structural and dynamic twist, as well as wake model are only secondary in terms of impact on damping. Resolution suffered from failure of system identification methods to extract reliable damping values from various non-linear response simulations.
C6: Frequency analysis of tangential force measurements on a vertical axis wind turbine
Morgan Rossander | Uppsala University | Sweden
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Authors:
Morgan Rossander | Uppsala University | Sweden
Anders Goude | Uppsala University | Sweden
Hans Bernhoff | Uppsala University | Germany
Sandra Eriksson | Uppsala University | Sweden
This paper presents experimental results of the torque ripple obtained from a three bladed 12 kW H-rotor prototype. The measurements are performed by means of load cells installed on the base of the struts and by electrical measurements on the generator. The resulting torques are analysed in terms of frequency spectrum and order spectrum synchronized with rotation). The measurements are compared to aerodynamic simulations of the turbine. The expected large torque ripple at three times the rotational speed (3p) is only weakly represented at the hub and in the generator. This suggests that the system is filtering the ripple and/or that the simulations are overestimating the 3p component. The torque ripple loads on the drive train are therefore lower than anticipated. Even if highly attenuated, most of the low frequencies correlating to aerodynamics are still represented in the generator electrical torque. This opens for possible online monitoring of unbalances in the turbine.
C7: A MIMO Periodic ARX identification algorithm for the Floquet stability analysis of wind turbines
Riccardo Riva | POLITECNICO DI MILANO | Italy
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Authors:
Riccardo Riva | POLITECNICO DI MILANO | Italy
Dr. Stefano Cacciola | Italy
Carlo Luigi Bottasso | Italy
The paper presents a new stability analysis approach applicable to wind turbines. At first, a reduced order periodic model is identified from response time histories, and then stability is assessed using Floquet theory. The innovation of the proposed approach is in the ability of the algorithm to simultaneously consider multiple response time histories, for example in the form of measurements recorded both on the rotor and in the stand still system. As each different measurement carries a different informational content on the system, the simultaneous use of all available signals improves the quality and robustness of the analysis. The identification algorithm has guaranteed stability properties, and allows for the mitigation of mode contamination problems. The accuracy of the algorithm has been tested on a simplified wind turbine model, in the entire partial load region II.
C8: A novel method of strain - bending moment calibration for blade testing
Dr. Peter Greaves | ORE Catapult | United Kingdom
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Authors:
Dr. Peter Greaves | ORE Catapult | United Kingdom
Raul Prieto | United Kingdom
Paul McKeever | United Kingdom
Cornelis van Beveren | United Kingdom
Robert Dominy | United Kingdom
Grant Ingram | United Kingdom
A new method of interpreting strain data in full scale static and fatigue tests has been implemented as part of the Offshore Renewable Energy Catapult’s ongoing development of biaxial fatigue testing of wind turbine blades. During bi-axial fatigue tests, it is necessary to be able to distinguish strains arising from the flapwise motion of the blade from strains arising from the edgewise motion. The method exploits the beam-like structure of blades and is derived using the equations of beam theory. It has been demonstrated to offer two principal advantages over the current state of the art method of calibrating strain gauges - It allows more than four strain gauge readings to be taken into account and it also considers the angle of the winch cables.
C9: Assessment of fatigue load alleviation potential through blade trailing edge morphing
Dr. Dimitris Manolas | National Technical University of Athens | Greece
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Authors:
Dr. Dimitris Manolas | National Technical University of Athens | Greece
Theofanis Tsiantas | Greece
Theodore Machairas | Greece
Anargyros Karakalas | Greece
Vasilis A. Riziotis | Greece
Dimitrios Saravanos | Greece
Spyros Voutsinas | Greece
The possibility of alleviating wind turbine loads through blade trailing edge shape morphing is investigated in the present paper. Emphasis is put on analyzing the effect of the trailing edge flap geometry on load reduction levels. The choice of the shape deformation of the camber line as well as the chordwise and spanwise dimensions of the trailing edge flap are addressed. The analysis concerns the conceptual DTU 10 MW RWT. Aeroelastic control of loads is materialized through a standard individual flap controller. Furthermore, a combined individual pitch-flap controller is evaluated and found to present advantages compared to the flap only controller. Flapwise fatigue load reduction ranging from 10% to 20%, depending on wind velocity and configuration considered, is obtained. Better performance is achieved by the combined pitch-flap controller.
C10: Assessment of synthetic winds through spectral modelling and validation using FAST
Abhijit Chougule | University of Agder | Norway
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Authors:
Abhijit Chougule | University of Agder | Norway
Surya Kandukuri | Norway
Hans Georg Beyer | Norway
In this paper, we analyse the simulated and measured wind data with respect to their spectral characteristics and their effect on wind turbine loads. The synthetic data is generated from a stochastic full-field turbulent wind simulator - TurbSim for neutral stability conditions. We first investigate a model for velocity spectra and, a coherence model, by comparing the model results with the measurements. In the second part we analyse the synthetic data via spectra and coherence for two cases; without and with adding coherent events. Finally, we compare wind turbine loads calculated by using FAST simulation of 5 MW reference wind turbine on the basis of simulated and measured data for the given mean wind speed.
C11: Effect of Turbulence on Power for Bend-Twist Coupled Blades
Alexander Stäblein | Technical University of Denmark | Denmark
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Authors:
Alexander Stäblein | Technical University of Denmark | Denmark
Morten H. Hansen | Denmark
Bend-twist coupling of wind turbine blades reduces the structural loads of the turbine but it also results in a decrease of the annual energy production. The main part of the power loss can be mitigated by pretwisting the blade, but some power loss remains and previous studies indicate that it might be related to the dynamic response of bend-twist coupled blades in turbulent flow. This paper contains estimations of the power curve from nonlinear time simulations, a linear frequency domain based method and a normal distribution weighted average method. It is shown that the frequency domain based estimation is highly dependant on the validity of the linearized model, thus estimations are poor for operational points close to rated wind speed. The weighted average method gives good results if an appropriate standard deviation is known a priori. The nonlinear time simulations show that changes in power due to turbulence are similar for coupled and uncoupled blades.
C12: Simulating the dynamic behavior of a vertical axis wind turbine operating in unsteady conditions
Enrico Benini | University of Trento | Italy
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Authors:
Enrico Benini | University of Trento | Italy
Lorenzo Battisti | Italy
Marco Raciti Castelli | Italy
Alessandra Brighenti | Italy
Giuseppe Soraperra | Italy
The present work aims at assessing the reliability of a simulation tool capable of computing the unsteady rotational motion and the associated tower oscillations of a variable speed VAWT immersed in a coherent turbulent wind. As a matter of fact, since the dynamic behaviour of a variable speed turbine strongly depends on unsteady wind conditions (wind gusts), a steady state approach can't accurately catch transient correlated issues. The simulation platform proposed here is implemented using a lumped mass approach: the drive train is described by resorting to both the polar inertia and the angular position of rotating parts, also considering their speed and acceleration, while rotor aerodynamic is based on steady experimental curves. The ultimate objective of the presented numerical platform is the simulation of transient phenomena, driven by turbulence, occurring during rotor operation, with the aim of supporting the implementation of efficient and robust control algorithms.
E1: Yawing characteristics during slippage of the nacelle of a multi MW wind turbine
Moo-Gyn Manuel Kim | Hamburg University of Applied Sciences | Germany
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Authors:
Moo-Gyn Manuel Kim | Hamburg University of Applied Sciences | Germany
Peter Dalhoff | Germany
Peter Gust | Germany
High aerodynamic yaw loads coupled with electrical failures in the wind turbine can result to a slippage of the nacelle, due to limited braking capabilities of the yaw system. A slippage on the other hand can lead to a mechanical malfunction of the yaw system. To analyse the yawing characteristics of a wind turbine during nacelle slippage situations, a detailed multibody system model of the yaw system has been developed and incorporated in a multibody system model of a wind turbine based on a 3.3 MW turbine. Extreme load cases which lead to a nacelle slippage have been simulated. The dynamics and loads on dierent wind turbine components are presented and discussed. First results show minimal load increases of the rotor torque and the bending moments of the blade root sections during slippage but unfavourable rotational speeds of the yaw drives.
E2: Impact of Wind Turbine Yaw misalignment on the Loads and Wind Farm Levelized Cost of Energy
Mike van Dijk | TU Delft | Netherlands
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Authors:
Mike van Dijk | TU Delft | Netherlands
Jan-Willem van Wingerden | Netherlands
Turaj Ashuri | Netherlands
Yaoyu Li | Netherlands
Mario Rotea | Netherlands
To make wind energy cost competitive with traditional resources, wind turbines are commonly placed in groups. Aerodynamic interaction between the turbines causes sub-optimal energy production. A control strategy to mitigate these losses is by redirecting the wake by yaw misalignment. This paper aims to assess the influence of load variations of the rotor due to partial wake overlap and presents a combined optimization of the power and loads using wake redirection. For this purpose, a computational framework is designed which computes the wind farm power production and the wind turbine rotor loads based on the yaw settings. The simulation results show that partial wake overlap can significantly increase asymmetric loading of the rotor disk and that yaw misalignment is beneficial in situations where the wake can be sufficiently directed away from the downstream turbine.
E3: Roadmap to the multidisciplinary design, analysis and optimisation of wind energy systems
Sebastian Sanchez Perez-Moreno | TU Delft | Netherlands
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Authors:
Sebastian Sanchez Perez-Moreno | TU Delft | Netherlands
Michiel Bastiaan Zaayer | Netherlands
Carlo Luigi Bottasso | Netherlands
Frederik Zahle | Netherlands
Gerardus Joseph Wilhelmus van Bussel | Netherlands
Katherine Dykes | Netherlands
Karl Otto Merz | Netherlands
Pierre-Elouan Réthoré | Netherlands
Sebastian Sanchez Perez-Moreno | Netherlands
A research agenda is described to further encourage the application of Multidisciplinary Design Analysis and Optimisation (MDAO) methodologies to wind energy systems. As a group of researchers closely collaborating within the International Energy Agency (IEA) Wind Task 37 for Wind Energy Systems Engineering: Integrated Research, Design and Development, we have identied challenges that will be encountered by users building an MDAO framework. This roadmap comprises 17 research questions and activities recognised to belong to three research directions: model fidelity, system scope and workflow architecture. It is foreseen that sensible answers to these questions will enable to more easily apply MDAO in the wind energy domain. Beyond the agenda, this work also promotes the use of systems engineering to design, analyse and optimise wind turbines and wind farms, to complement existing compartmentalised research and design paradigms.
E4: Optimization Under Uncertainty of Site-Specific Turbine Configurations
Katherine Dykes | United States
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Authors:
Julian Quick | National Renewable Energy Laboratory | United States
Fredrik Zahle | United States
Peter Grad | United States
Katherine Dykes | United States
Uncertainty affects many aspects of wind energy plant performance and cost. In this study, we explore opportunities for site-specific turbine configuration optimization that accounts for uncertainty in the wind resource. As a demonstration, a simple empirical model for wind plant cost of energy is used in an optimization under uncertainty to examine how different risk appetites affect the optimal selection of a turbine configuration for sites of different wind resource profiles. If there is unusually high uncertainty in the site wind resource, the optimal turbine configuration diverges from the deterministic case and a generally more conservative design is obtained with increasing risk aversion on the part of the designer.
E5: Analysis of different blade architectures on VAWT performance
Prof. Lorenzo Battisti | University of Trento | Italy
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Authors:
Prof. Lorenzo Battisti | University of Trento | Italy
Marco Raciti Castelli | Italy
Enrico Benini | Italy
Alessandra Brighenti | Italy
The present paper aims at describing and comparing different small Vertical Axis Wind Turbine (VAWT) architectures, in terms of performance and loads. These characteristics can be highlighted by resorting to the Blade Element-Momentum (BE-M) model, commonly adopted for rotor pre-design and controller assessment. After validating the model with experimental data, the paper focuses on the analysis of VAWT loads depending on some relevant rotor features: blade number (2 and 3), airfoil camber line (comparing symmetrical and asymmetrical profiles) and blade inclination (straight versus helical blade). The effect of such characteristics on both power and thrusts (in the streamwise direction and in the crosswise one) as a function of both the blades azimuthal position and their Tip Speed Ratio (TSR) are presented and widely discussed.
G2: Determining Diffuser Augmented Wind Turbine performance using a combined CFD/BEM method
Joss Kesby | The University of Newcastle, Australia | Australia
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Authors:
Joss Kesby | The University of Newcastle, Australia | Australia
Philip Clausen | Australia
David Bradney | Australia
Mu Chu | Australia
The optimisation of a Diffuser Augmented Wind Turbine has traditionally focused on maximising its power output. Optimising the design of the blade and the shape of the diffuser for maximum turbine power over a range of wind velocities is a complex process as each will influence the others flow regime. In this paper we propose a method that combines the predictions of flow through a diffuser, using computational fluid dynamics, and the flow from a turbine blade using a modified blade element theory to predict the power output of a diffuser augmented wind turbine. Good agreement was found between the predictions from this new method and experimental data from the literature.
G3: Analysis of Dynamic Interactions between Different Drivetrain Components in a Detailed Wind Turbine Model
Arne Bartschat | Fraunhofer IWES | Germany
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Authors:
Arne Bartschat | Fraunhofer IWES | Germany
Marcel Morisse | Germany
Axel Mertens | Germany
Jan Wenske | Germany
The presented work describes a detailed analysis of the dynamic interactions among mechanical and electrical drivetrain components of a modern wind turbine under the influence of parameter variations, different control mechanisms and transient excitations. For this study, a detailed model of a 2MW wind turbine with a gearbox, a permanent magnet synchronous generator and a full power converter has been developed which considers all relevant characteristics of the mechanical and electrical subsystems. The analysis shows that, considering control measures based on active torsional damping, interactions between mechanical and electrical subsystems can significantly affect the loads and thus the individual lifetime of the components.
G4: Comparison of computational modelling and field testing of a small wind turbine operating in unsteady flows
Samuel Evans | The University of Newcastle | Australia
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Authors:
Samuel Evans | The University of Newcastle | Australia
David Bradney | Australia
Philip Clausen | Australia
Samuel Evans | Australia
Mariana Salles Pereira Da Costa | Australia
Small horizontal-axis wind turbines are likely to operate in a broad range of operating flow conditions, often in highly turbulent flow, due, in part, to their varied site placements. This paper compares the computational simulations of the performance of a 5 kW horizontal-axis wind turbine to detailed field measurements, with a particular focus on the impact of unsteady operating conditions on the drivetrain performance and generator output. Results indicate that the current Blade Element Momentum Theory based aerodynamic models under-predict the effect of high turbine yaw on the rotor torque, leading to a difference between predicted and measured shaft speed and power production. Furthermore, the results show discrepancies between the predicted instantaneous turbine yaw performance and measurements.
G5: Derivation and analysis of the analytical velocity and vortex stretching expressions for an O(N logN)-FMM
Tom Berdowski | Delft University of Technology | Netherlands
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Authors:
Tom Berdowski | Delft University of Technology | Netherlands
Jens Walther | Netherlands
Carlos Ferreira | Netherlands
Fanzhong Meng | Netherlands
A method for deriving the analytical expressions for the velocity and vortex stretching terms as a function of the spherical multipole expansion approximation of the vector potential is presented. These terms are essential in the context of 3D Lagrangian Vortex Particle Methods combined with fast summation techniques. The convergence and computational efficiency of this approach is assessed in the framework of an Nlog N-type Fast Multipole Method (FMM), by using vorticity particles to simulate a system of coaxial vortex rings for which also the exact results are known. It is found that the current implementation converges rapidly to the exact solution with increasing expansion order and acceptance factor. An investigation into the computational efficiency demonstrated that the Nlog N-type FMM is already viable for a particle size of only several thousands and that this speedup increases significantly with the number of particles. Finally, it is shown that the implementation of the FMM with the current analytical expressions is at least twice as fast as when opting for using even the simplest implementation of finite differences instead.
G6: CFD modeling of a large dimension WF cluster using precursor inlet condition
Prof. José M.L.M. Palma | University of Porto /Faculty of Engineering (NIF 501413197) | Portugal
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Authors:
Prof. José M.L.M. Palma | University of Porto /Faculty of Engineering (NIF 501413197) | Portugal
Vitor Gomes | Portugal
The accuracy of Computational Fluid Dynamics (CFD) models for Atmospheric Boundary Layer (ABL) flows relies largely on the placement of the domain boundaries and the quality of the imposed flow conditions, the inlet boundary in particular. Exploiting the parabolic nature of many ABL flows and of CFD modelled ABL flow in particular, a precursor simulation is used as source of flow data to improve the target domain's inlet flow description over the standard synthetic boundary conditions, one-directionally coupling the solutions to the two simulations. Using the approach, a case of flow over a two wind farm offshore cluster is modelled using two small coupled simulations, matching the results of a single simulation including the full cluster at a significant computational time saving, in the order of 70%. Further savings were shown to be possible by reducing the resolution of the precursor simulation, with negligible impact on the results at the target domain.
G7: Calibration of the γ−Equation Transition Model for High Reynolds Flows at Low Mach
Dr. Simone Colonia | University of Glasgow | United Kingdom
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Authors:
Dr. Simone Colonia | University of Glasgow | United Kingdom
Vladimir Leble | United Kingdom
Rene Steijl | United Kingdom
George Barakos | United Kingdom
The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients that need tuning. In this paper, the one-equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications.
G8: Wake modeling in complex terrain using a hybrid Eulerian-Lagrangian approach
Dr. Franz Georg Fuchs | SINTEF | Norway
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Authors:
Dr. Franz Georg Fuchs | SINTEF | Norway
Mandar Tabib | Norway
Adil Rasheed | Norway
Eivind Fonn | Norway
Wake vortices (WV) generated by aircraft are a source of risk to the following aircraft. The probability of WV related accidents increases in the vicinity of airport runways due to the shorter time of recovery after a WV encounter. Hence, solutions that can reduce the risk of WV encounters are needed to ensure increased flight safety. In this work we propose an interesting approach to model such wake vortices in real time using a hybrid Eulerian-Lagrangian approach. We derive an appropriate mathematical model, and show a comparison of the different types of solvers. We will conclude with a real life application of the methodology by simulating how wake vortices left behind by an aircraft at the Værnes airport in Norway get transported and decay under the influence of a background wind and turbulence field. Although the work demonstrates the application in an aviation context the same approach can be used in a wind energy context.
G9: Coupling of electromagnetic and structural dynamics for a wind turbine generator
Daniel Matzke | RWTH Aachen University | Germany
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Authors:
Daniel Matzke | RWTH Aachen University | Germany
Sebastian Hollas | Germany
Ralf Schelenz | Germany
Georg Jacobs | Germany
Sebastian Rick | Germany
Kay Hameyer | Germany
This contribution presents a model interface of a wind turbine generator to represent the reciprocal effects between the mechanical and the electromagnetic system. Therefore, a multi-body-simulation (MBS) model in Simpack is set up and coupled with a quasi-static electromagnetic (EM) model of the generator in Matlab/Simulink via co-simulation. The MBS model and the interface are set up in such a way that the EM forces can be applied to the structure and the response of the structure can be fed back to the EM model. Finally the results of this co-simulation are presented in this contribution and possible future work is discussed.
G10: Floating substructure flexibility of large-volume 10MW offshore wind turbine platforms
Michael Borg | Technical University of Denmark | Denmark
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Authors:
Michael Borg | Technical University of Denmark | Denmark
Anders Melchior Hansen | Denmark
Henrik Bredmose | Denmark
Designing floating substructures for the next generation of 10MW and larger wind turbines has introduced new challenges in capturing relevant physical effects in dynamic simulation tools. In achieving technically and economically optimal floating substructures, structural flexibility may increase to the extent that it becomes relevant for wind turbine loads, which has so far been has not been included in dynamic simulations. This paper describes a method for the inclusion of substructural flexibility in aero-hydro-servo-elastic dynamic simulations for large-volume substructures, including wave-structure interactions, to form the basis of deriving sectional loads and stresses within the substructure. The method is applied to a case study to illustrate the implementation and relevance.
G11: Modelling of Vortex-Induced Loading on a Single-Blade Installation Setup
Dr. Witold Skrzypiński | DTU | Denmark
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Authors:
Dr. Witold Skrzypiński | DTU | Denmark
Mac Gaunaa | Denmark
Joachim Christian Heinz | Denmark
Vortex-induced integral loading fluctuations on a single suspended blade at various inflow angles were modeled in the presents work by means of stochastic modelling methods. The reference time series were obtained by 3D DES CFD computations carried out on the DTU 10MW reference wind turbine blade. The reference time series varied significantly, depending on the inflow angle. This made the modelling of all the time series with a single and relatively simple engineering model challenging. In order to find model parameters, optimizations were carried out, based on the root-mean-square error between the Single-Sided Amplitude Spectra of the reference and modelled time series. In order to model well defined frequency peaks present at certain inflow angles, optimized sine functions were superposed on the stochastically modelled time series. The modelled and reference time series showed a satisfactory agreement.
G12: Numerical simulations of the NREL s826 airfoil
Kristian Sagmo | NTNU | Norway
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Authors:
Kristian Sagmo | NTNU | Norway
Lars Roar Sætran | Norway
Jan Michael Simon Bartl | Norway
2D and 3D steady state simulations were done using the commercial CFD package Star-CCM+ with three different RANS turbulence models. Lift and drag coefficients were simulated at different angles of attack for the NREL S826 airfoil at a Reynolds number of 100 000, and compared to experimental data obtained at NTNU and at DTU. A grid refinement study allowed an estimation of simulation errors due to numerical discretization. The Spalart-Allmaras turbulence model reproduced experimental results from wing surface pressure measurements well in the 2D simulations. The 3D simulations with Realizable two-layer k-epsilon model predicted essentially the same lift coefficients as Spalart-Allmaras. From the conducted 3D simulations surface pressure predictions along the wing span were presented, along with volumetric renderings. Both showed a high degree of span wise flow variation when going into the stall region, and predicted a flow field resembling that of stall cells for angles of attack above 8.5 degrees.
G13: Modeling the transient aerodynamic effects during the motion of a flexible trailing edge
Torben Wolff | ForWind - Institute of Turbomachinery and Fluid Dynamics | Germany
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Authors:
Torben Wolff | ForWind - Institute of Turbomachinery and Fluid Dynamics | Germany
Joerg R. Seume | Germany
Wind turbine blades have been becoming longer and more slender during the last few decades. The longer lever arm results in higher stresses at the blade root. Hence, the unsteady loads induced by turbulence, gust, or wind shear increase. One promising way to control these loads is to use flexible trailing edges near the blade tip. The unsteady effects which appear during the motion of a flexible trailing edge must be considered for the load calculation during the design process because of their high influence on aeroelastic effects. This is not yet possible in most of the wind turbine simulation environments. Consequently, an empirical model is developed in the present study which accounts for unsteady effects during the motion of the trailing edge. The model is based on Fourier analyses of results generated with Reynolds-Averaged Navier-Stokes (RANS) simulations of a typical thin airfoil with a deformable trailing edge.
G15: Modelling Horns Rev wind farm with the Actuator Line Model with coarse resolution
Dr. Martín Draper | Universidad de la República | Uruguay
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Authors:
Dr. Martín Draper | Universidad de la República | Uruguay
Andrés Guggeri | Uruguay
Gabriel Usera | Uruguay
Actuator models have been used to represent the presence of wind turbines in a simulation in the past few years. The Actuator Line Model (ALM) has shown to reproduce with reasonable accuracy the wind flow through wind turbines under different operational conditions. Nevertheless, there are not many simulations of wind farms performed with the ALM mainly because of its computational cost. The aim of the present paper is to evaluate the ALM in spatial resolutions coarser than what is generally recommended, also using larger time steps, in a simulation of a real wind farm. To accomplish this, simulations of one row of Horns Rev wind farm are performed, for different wind directions. It is concluded that the ALM is able to capture the main features of the interaction between wind turbines relaxing its resolution requirements. A sensitivity analysis is performed to assess the influence of the smearing factor and the spatial resolution.
G17: Modelling flows within forested areas using the k-epsilon RaNS model
Prof. José M.L.M. Palma | University of Porto /Faculty of Engineering (NIF 501413197) | Portugal
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Authors:
Prof. José M.L.M. Palma | University of Porto /Faculty of Engineering (NIF 501413197) | Portugal
Joao Viana Lopes | Portugal
Alexandre Silva Lopes | Portugal
A new canopy model for the RaNS method with the k-epsilon turbulence model was developed. To derive the effect of vegetation on the transport of turbulent quantities, it uses a Taylor series expansion of the velocity magnitude and assumes that the turbulent kinetic energy is much smaller than the kinetic energy of the mean flow. The resultant model is composed by a sum of velocity moments of increasing order. It was expected that a truncated sum, including only terms that can be expressed using quantities available within the k-epsilon model, would provide better accuracy than traditional models based on dimensional arguments. However, the results mimic those obtained with a model based on dimensional arguments, calibrated using results of large-eddy simulations, proving the validity of both approaches and showing that the accuracy in the modelling of the flows over vegetation is limited by the k-epsilon model itself and not by the modelling of vegetation effects on turbulence.
G18: Reliability of numerical wind tunnels for VAWT simulation
Dr. Marco Raciti Castelli | University of Padova | Italy
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Authors:
Dr. Marco Raciti Castelli | University of Padova | Italy
Massimo Masi | Italy
Lorenzo Battisti | Italy
Enrico Benini | Italy
Alessandra Brighenti | Italy
Vincenzo Dossena | Italy
Giacomo Persico | Italy
Computational Fluid Dynamics (CFD) based on the Unsteady Reynolds Averaged Navier Stokes (URANS) equations have long been widely used to study vertical axis wind turbines (VAWTs). Following a comprehensive experimental survey on the wakes downwind of a troposkien-shaped rotor, a campaign of 2D simulations is presented here, with the aim of assessing its reliability in reproducing the main features of the flow, also identifying areas needing additional research. Starting from both a well consolidated turbulence model (k-omega SST) and an unstructured grid typology, the main simulation settings are here manipulated in a convenient form to tackle rotating grids reproducing a VAWT operating in an open jet wind tunnel. The dependence of the numerical predictions from the selected grid spacing is investigated, thus establishing the less refined grid size that is still capable of capturing some relevant flow features such as integral quantities (rotor torque) and local ones (wake velocities).
G19: Enhanced method for multi-scale wind simulations over complex terrain for wind resource assessment
Dr. Alex Flores-Maradiaga | Technical University Federico Santa Maria | Chile
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Authors:
Dr. Alex Flores-Maradiaga | Technical University Federico Santa Maria | Chile
Robert Benoit | Chile
Christian Masson | Chile
Due to the natural variability of the wind and its heavy reliance on local atmospheric conditions, it is necessary to conduct thorough wind resource assessments to determine how much energy can be extracted from the wind at a given site. Usually advanced high resolution multiscale models capable of simulating wind patterns over steep complex terrain are required to evaluate this fluctuating energy potential. For this purpose, an enhanced numerical method was devised and adapted in the compressible non-hydrostatic atmospheric model MC2 of Environment Canada, with imbedded large-eddy simulation (LES) capabilities for wind modeling over topography. This implementation has been verified and validated numerically by simulating the neutrally stratified atmospheric boundary layer (ABL) over idealized flat and mountainous terrain. From these tests it has been found that this new multiscale method yields good results when compared with similar models that employ computationally intensive methods. This enhanced method now has the ability to solve multiscale structures using new wind initialization and time discretization schemes that allow more stable and accurate numerical modeling. The resulting model can be used to assess the wind resource at local, regional and subcontinental scales, reducing significantly the wind speed overestimation in mountainous areas.
I1: Fluid-Structure interaction analysis and performance evaluation of a membrane blade
Mehran Saeedi | TU München | Germany
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Authors:
Mehran Saeedi | TU München | Germany
Roland Wüchner | Germany
Kai-Uwe Bletzinger | Germany
Examining the potential of a membrane blade concept is the goal of the current work. The surface of the membrane blade is made from pre-tensioned membranes meeting at the pre-tensioned cable at the trailing edge. Two-way coupled fluid-structure interaction analysis is necessary for evaluation of the aerodynamic performance of such a configuration. The main aerodynamic characteristics of the membrane blade including lift coefficient, drag coefficient and lift to drag ratio are compared with its rigid counterpart. A single non-rotating NREL phase VI blade is studied as a first step towards analyzing the concept for the rotating case. The membrane blade has a higher slope of the lift curve. For higher angles of attack, lift and drag coefficients as well as the lift to drag ratio is higher for the membrane blade. A single non-rotating blade is studied here as a first step towards analyzing the concept for the rotating case.
I2: CFD Analysis of a Finite Linear Array of Savonius Wind Turbines
Prof. Marius Paraschivoiu | Concordia University | Canada
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Authors:
Prof. Marius Paraschivoiu | Concordia University | Canada
Belabes Belkacem | Canada
Vertical axis wind turbines such as Savonius rotors have been shown to be suitable for low wind speeds normally associated with wind resources in all corners of the world. However, the efficiency of the rotor is low. This paper presents results of Computational Fluid Dynamics (CFD) simulations for an array of Savonius rotors that show a significant increase in efficiency. It looks at identifying the effect on the energy yield of a number of turbines placed in a linear array. Results from this investigation suggest that an increase in the energy yield could be achieved which can reach almost two times than the conventional Savonius wind turbine in the case of an array of 11turbines with a distance of 1.4R in between them. The effect of different TSR values and different wind inlet speeds on the farm has been studied for both a synchronous and asynchronous wind farm.
I3: Numerical Study on the Effect of Swept Blade on the Aerodynamic Performance of Wind Turbine at High Tip Speed Ratio
Prof. Hua Yang | Yangzhou University | China
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Authors:
Prof. Hua Yang | Yangzhou University | China
Feng Wang | China
Hongmei zuo | China
Chao Liu | China
The current situation is that the development of high speed wind energy saturates gradually, therefore, it is highly necessary to develop low speed wind energy. This paper, based on a specific straight blade and by using Isight which integrates ICEM and CFD, optimizes the blade stacking line and acquires the best swept blade shape. It is found that power coefficient Cp of swept blade is 3.2% higher than that of straight blade at the tip speed ratio of 9.82, that the thrust of swept blade receives is obviously less than that of straight blade, better stabilizing wind turbine, and that inflow angle of attack increases producing 'wing tip effect' in favor of improving the output torque of swept blade at low speed condition.
I4: Evaluation of an Integrated Roof Wind Energy System for urban environments
Diana Kiss | IBIS Power | Netherlands
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Authors:
Diana Kiss | IBIS Power | Netherlands
Balkrishna Patankar | Netherlands
Ramavtar Tyagi | Netherlands
Alexander B. Suma | Netherlands
Integrating renewable energy in the urban environment is of importance for the renewable energy goals set by the European Union. This research is to study and evaluate wind energy potential for an Integrated Roof Wind Energy System on the rooftop of the buildings of different heights and in different locations with the help of numerical modelling (CFD). The Navier-Stokes equations are solved using the SIMPLE algorithm while the turbulence is modelled using the k-ω-SST equations. All the simulations are performed using OpenFOAM. Results shows that wind speed can be accelerated by ~1.4 times till it reaches the periphery of the turbine inside the unit, which will increase wind power output considerably. This results in power factor increase of 1.7 for tall buildings. Therefore, enabling combined micro wind and solar energy systems to be a viable option for urban environments.