bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and evaluation of rotor blades for fluid structure interaction studies in wind tunnel conditions
Authors: Langidis A , Nietiedt S , Berger F , Kröger L , Petrović V , Wester T T B , Gülker G , Göring M , Rofallski R , Luhmann T , Kühn M
Published: June 2022

Wind tunnel experiments with wind turbine models are a promising method for investigating fluid structure interaction (FSI) phenomena. However, the lack of suitable models that feature properly scaled blades and the complexity of aeroelastic and fluid dynamic measurements during turbine operation is challenging. In this paper, the design methodology for aeroelastically scaled blades which are intended for Model Wind Turbine Oldenburg (MoWiTO) 1.8 is presented. The scaling relations are formulated, initiating from the existing turbines’ design. Next, the manufactured blades are equipped on MoWiTO and are subsequently evaluated, during operation under gusty wind fields produced by an active grid. The tip deflection is recorded using an innovative photogrammetry setup. Simulations of an OpenFAST model, which has properties extracted from the scaling formulation, are used as reference. The recorded loads and blade deformations show similar dynamics, compared to the reference. These results prove the design successful, and the capability of measuring FSI phenomena in wind tunnel environment is showcased.
WindsPT e-Science platform for wind measurement campaigns
Authors: Gomes D F , Lopes J C , Palma J M L M , Senra F , Dias S , Coimbra I L
Published: June 2022

Experimental field campaigns for collecting wind data, essential for academic research and the wind energy industry, are non-trivial due to the complex equipment and infrastructure required. This paper reports the latest developments of the WindsPT e-Science platform for planning, executing, and disseminating wind measurement campaign data. Existing e-Science platforms have been developed for more generic domains, preventing them from capturing the details and requirements of the field. Additionally, we propose a protocol for transferring large volumes of data from the in-site devices to our platform, ensuring data replication. With an easy-to-use Web interface, WindsPT promotes collaboration between participants, disseminates results among the stakeholders, publishes metadata, uses DOI, and includes metadata that enables machine-to-machine communication. The platform has multiple sections, with maps, images, and documents, where there is information about the location of the stations, positioning of the sensors, operating dates, photos, technical sheets, calibration documents, among others. The WindsPT platform has been used to host the Perdigão 2017 experimental campaign and proved to be a valuable tool during all the phases of this large field experiment. A new version of WindsPT, designed to be FAIR, host multiple campaigns, and include multiple cross-campaign shared features, as full-text search capabilities, is now developed and tested.
Wind Tunnel Experiment to Study Aerodynamics and Control of H-Rotor Vertical Axis Wind Turbine
Authors: Jafari M , Sakib M S , Griffith D T , Brownstein I , Strom B , Cooney J
Published: June 2022

This study focuses on wind tunnel testing of a 3-bladed H-rotor vertical axis wind turbine (VAWT) under various conditions. Different performance metrics such as power coefficient (CP
), thrust load coefficient (CX
), and lateral load coefficient (CY
) are presented at four wind speeds. Parked loads, which are key parameters in designing VAWTs, are reported for the baseline case. Apart from presenting the benchmark results for the baseline model, the impact of two control strategies to boost the energy production of the VAWT are investigated. First, the effect of installing the plasma actuators on all blades is tested at four plasma input voltages. The results indicate that plasma actuators are an efficient approach to enhance the aerodynamic efficiency of VAWTs through modification of drag and lift loads acting on the blades. The second control strategy evaluated is intracycle RPM control. In this control method, the rotational speed of the turbine is varied with the azimuthal location of blades at each cycle so that the power production is increased. The results observed for this control strategy encourage further research development to expand the limited knowledge on its application for VAWTs.
POD analysis of the wake dynamics of an offshore floating wind turbine model
Authors: Raibaudo C. , Piquet T. , Schliffke B. , Conan B. , Perret L.
Published: June 2022

The wake dynamics of a floating wind turbine model experiencing realistic surge motion and immersed within a properly scaled atmospheric boundary layer is studied through wind tunnel experiments. The turbine is modelled by a porous disk representing the floating 2MW wind turbine located at the offshore test site in Le Croisic (France). Experiments were conducted in the LHEEA’s atmospheric wind tunnel. A surge motion is imposed on the model, using a linear actuator, to replicate realistic behaviors under wave swell. Realistic frequencies of actuation are considered to study their effects on the wake properties. The wake is characterized using Stereoscopic Particle Image Velocimetry (SPIV) measurements in a y - z plane normal to the flow, at two different streamwise locations x = 4.6D and 8.1D. In addition to the documentation of the main wake statistics, the velocity fields are analyzed using Proper Orthogonal Decomposition (POD). The velocity field is decomposed into a set of spatial and temporal modes. The eigenvalues convergence is shown to be relatively slow, due to the high Reynolds number turbulent boundary layer within which the model is immersed. When varying the surge motion frequency, the spatial modes do not show any significant change in shape and amplitude. However, the spectral analysis performed on the temporal modes shows the emergence of peaks at the surge motion frequency and the overall increase of the low-frequency energy content in the Power Spectral Density, in particular for the highest frequencies of motion tested.
An experimental system to acquire aeroacoustic properties on wind turbine blades
Authors: Deparday J , Müller H , Polonelli T , Barber S
Published: June 2022

Wind turbine noise is a key issue preventing the successful exploitation of the full potential of wind energy throughout the world, especially in urban areas. To better assess and predict wind turbine noise, several aeroacoustic simulations and models have been developed over the past. Many semi-empirical models for noise emission and propagation rely on aeroacoustic properties at the blade level, including the pressure gradient, the spectrum of the pressure fluctuations, the convection velocity and the coherence lengths. Field measurements of these local quantities on operating wind turbines are valuable to improve the accuracy of the models. In the Aerosense project, a cost-effective smart measurement system is being developed that is thin, easy to install without damaging the blade, low power, self-sustaining and wirelessly transmitting. This measurement system uses MEMS sensors, which require some calibrations and corrections to obtain sufficiently accurate data. This paper describes the experimental system and its workflow, which has been developed within the Aerosense project to obtain sufficiently accurate measurements for semi-empirical noise emission and propagation models. The experimental system and its workflow are then validated in an anechoic wind tunnel on a NACA63-418 airfoil. The results show that this experimental system is able to acquire relevant aeroacoustic properties on operating wind turbines.
A comprehensive procedure to process scanning lidar data for engineering wake model validation
Authors: Hung Lin-Ya , Santos Pedro , Gottschall Julia
Published: June 2022

We propose a comprehensive methodology to incorporate filtering, interpolation and uncertainties estimation in the processing of scanning wind lidar data. A full-scale wake measurement campaign has been carried out at an 8-MW prototype wind turbine in Bremerhaven, Germany, to apply and demonstrate the procedure. The filtering and interpolation of the scanning lidar data results in an average scan that fully covers the turbine rotor swept area. Once the filtered scans are processed, all observations are clustered in a capture matrix, where each bin can be ensemble-averaged according to wind direction, atmospheric stability and turbulence intensity. The final bin-averaged results were compared to an engineering wake model projected onto the lidar’s beam directions, along with an uncertainty model which combines the contributions both from observations and simulation inputs. The results reveal the overall wake characteristics and the ability of the selected model to predict the wake under neutral conditions, with RMSE = 0.532 ms−1. Under stable conditions the model overestimates the wake deficit with greater RMSE = 1.108 ms−1. Nevertheless, we show that this post-processing methodology is effective and can be further applied in other long-range scanning lidar datasets, e.g., for offshore cluster wakes or blockage effect studies.
Contrast enhancement in thermographic flow visualization on wind turbines in operation
Authors: Gleichauf Daniel , Sorg Michael , Fischer Andreas
Published: June 2022

Thermographic flow visualization is a non-contact, non-invasive approach for assessing the aerodynamic state of wind turbine rotor blades and, as a result, the overall efficiency of the wind turbine. The distinguishability between the laminar and turbulent flow regimes in operating wind turbines cannot be easily increased intentionally and is totally dependent on the energy input from the sun. To deal with low-contrast measurement conditions and improve the distinguishability between flow regimes, advanced image processing using the feature extraction method principal component analysis is used. The image processing is applied to an image series of thermographic flow visualizations of a steady flow situation in a free-field experiment on a wind turbine in operation with a low distinguishability between the laminar and turbulent flow regime. The resulting feature images, based on the temporal intensity fluctuations in the images, are evaluated with regard to the global distinguishability between the laminar and turbulent flow regime. By applying the principal component analysis, the contrast-to-noise ratio was increased by a factor of 2.5. Furthermore, the resulting flow visualizations enable a localization of the laminar-turbulent flow transition, that is not possible in the raw data due to missing features in the intensity profile that allow a clear separation.
Wind tunnel study: is turbulent intensity a good candidate to help in bypassing low Reynolds number effects on 2d blade sections?
Authors: Mishra Rishabh , Neunaber Ingrid , Guilmineau Emmanuel , Braud Caroline
Published: June 2022

Wind turbines operate in the turbulent atmospheric boundary layer and can be additionally exposed to the wakes of upstream wind turbines. Hence the inflow encountered by wind turbine rotor blades is turbulent. One way to gain more knowledge on the impact of the turbulence on the airfoil aerodynamics is by studying a 2d airfoil section of a real wind turbine blade against inflows of various turbulence intensities and Reynolds numbers. Therefore, for the purpose of this paper, experiments were performed and aerodynamic coefficients were calculated for chord based Reynolds numbers between 1.3 × 105 and 3 × 105 and angles of attack between -10° and 24° for inflows of three different averaged turbulence intensities, 0.3%, 3% and 5.5%. Results were compared with the already available result of measurements done at a higher chord based Reynolds number of 4.7×106 for the same airfoil type. The results show that, for a given Reynolds number, an increase in turbulence intensity suppresses the flow separation. It was also found that an increase in the turbulence intensity of the inflow does reduce the dependence of aerodynamic coefficients on the Reynolds number. The Comparison between experimental results for lower chord-based Reynolds numbers and high chord-based Reynolds numbers shows differences which implies that an increase of the turbulence intensity is not enough to bypass the low Reynolds number effect completely.
Wind tunnel benchmark tests of airfoils
Authors: Bak Christian , Olsen Anders S. , Fischer Andreas , Lylloff Oliver , Mikkelsen Robert , Gaunaa Mac , Beckerlee Jimmie , Ildvedsen Sigurd , Vronsky Tomas , Grasso Francesco , Loeven Alex , Broersma Liekele , Akay Busra , Madsen Jesper , Hansen Rolf , Kommer Robert
Published: June 2022

This paper describes a benchmark of four airfoils in the Poul la Cour Tunnel (PLCT). The wind tunnel, the corrections used and the method of making adapters for the airfoils are also described. Very good agreement was in general observed between the measurements in PLCT and in other high quality wind tunnels. Some deviations were seen, but they were mainly attributed to the differences in separation on the airfoil. Apart from the benchmarking, this paper also highlights the challenges in testing airfoils in general such as obtaining 2D flow on thick airfoils that inherently shows separated flow and how to make adapters for airfoils tested in other wind tunnels.
Adaptive measuring trajectory for scanning lidars: proof of concept
Authors: Chen Yiyin , Yu Wei , Guo Feng , Cheng Po Wen
Published: June 2022

Application of nacelle-mounted long-range scanning lidars is facing the challenge that the nacelle motion causes deviations in the measuring trajectories. Such lidars are very sensitive to even the slightest trajectory deviation due to its long measuring range. Motivated by this need, we propose the concept of adaptive measuring trajectory and explore its use for eliminating the effect of the rotational motion of the lidar on the target measuring trajectory. This work first aims to experimentally test the performance of adaptive measuring trajectory under ideal conditions by installing a scanning lidar on a 6DOF motion platform to model the lidar motion on the turbine nacelle. The real trajectory with and without correction is measured by a camera. The comparison confirms that the adaptive measuring trajectory could stablize the target measuring trajectory given the lidar motion. Then, the possibility of using Kalman filter to estimate lidar motion given noisy motion measurements is investigated. The results show great potential of Kalman filter for lidar motion estimation, which could be very useful for its future application.
Detection and localization of flow separation on wind turbines by means of unsteady thermographic flow visualization
Authors: Oehme Felix , Sorg Michael , Fischer Andreas
Published: June 2022

For the first time, a thermographic detection and localization of turbulent flow separation on an operating wind turbine is presented and verified. Flow separation on wind turbine rotor blades causes power reduction, structural loads and increased noise emissions. In contrast to established methods for stall detection, the presented infrared thermographic measurement approach is non-invasive, in-process capable and provides a high spatial resolution. With respect to the state of the art for thermographic stall detection in wind tunnel experiments, the thermal surface response to unsteady inflow conditions is evaluated for measurements on an operating wind turbine, in order to achieve unambiguous thermographic features for the detection of flow separation. The evaluation of the thermodynamic response behavior shows a clear detection of flow separation by means of temperature fluctuation maxima in the regions of flow transition as well as an increasing temperature fluctuation within the separated flow region. In addition, a geometric assignment is conducted which enables a localization of the separation point with an uncertainty of 0.6% of the chord length. The detection and localization of flow separation is verified by means of tufts visualization.
Cross validation of the aerodynamic and acoustic measurements in two Kevlar-walled wind tunnels
Authors: Fischer Andreas , Bak Christian , Lylloff Oliver , Olsen Anders S. , Mikkelsen Robert F. , Ildvedsen Sigurd B. , Beckerlee Jimmy S. , Borgoltz Aurelien , Kuester Matthew , Intaratep Nanyaporn
Published: June 2022

The wind tunnel with Kevlar walls is becoming more and more popular for aeroacoustic measurements, because the necessary corrections to convert aerodynamic coefficients to free field values are moderate and at the same time the signal to noise ratio of acoustic measurements are in the same order as in an open jet configuration. Yet, the technology is new and the correction methods for aerodynamic and acoustic coefficients are not well established. This paper aims on bench-marking two of the largest Kevlar-walled wind tunnels by cross validation of the measurements performed on a NACA633018 aerofoil model. The measured aerodynamic coefficients showed and excellent agreement in the attached flow regime. Maximum lift was predicted differently in the two facilities. The differences might be due to three-dimensional effects for separated flow and the fact that the aspect ration was different in the two facilities. The difference of the measured overall sound pressure levels was less ± 1 dB for attached flow conditions. However, we observed a difference in the slope of the sound pressure spectra and recommend to further investigate the acoustic correction methods.
Comparison of different fidelity aerodynamic solvers on the IEA 10 MW turbine including novel tip extension geometries
Authors: Behrens de Luna R , Marten D , Barlas T , Horcas S G , Ramos-García N , Li A , Paschereit C O
Published: June 2022

Lifting-line based solvers could supersede the blade element momentum (BEM) method as the industry standard in the near future as rotor sizes of modern wind turbines and computational resources continue to increase. A comparison study between both methods is presented where the IEA 10 MW wind turbine is evaluated in the aero-servo-elastic simulation tool QBlade, comparing the lifting-line free vortex wake method to an unsteady blade element momentum solver. Besides the baseline rotor of the IEA 10 MW turbine, the comparison includes several blade tip extensions, including a swept and a dihedral geometry, to further differentiate capabilities between both methods in aerodynamically complex flow fields. As a reference serve results from equivalent simulations performed with multiple fidelity solvers of the simulation tool HAWC2. Results of a rigid load case demonstrate considerable improvement regarding the aerodynamic accuracy of lifting-line based methods in below rated conditions over BEM codes. The aerodynamic loads on geometrically complex tip extensions in steady conditions prove good capabilities of lower fidelity codes to predict out-of-plane bend shapes but also clear limitations regarding loads on swept geometries. A quasi-steady aeroelastic load case further demonstrates the capability of both QBlade codes to produce comparable results to similar fidelity solvers of the HAWC2 tool on an integral level. A detailed comparison in the time domain shows a larger dependency of the results on the type of structural solver that is used in contrast to the fidelity level of the aerodynamic method.
Structural Design of Wind Turbine Blades with an Additively Manufactured Graded Lattice Core using Topology Optimisation
Authors: Moss A , Macquart T , Panesar A , Forrest M , Greaves P , Pirrera A
Published: June 2022

Conventional wind turbine blade manufacture relies on large, expensive moulds. Instead, using additive manufacturing to print the internal structure of blades, upon which it would be possible to lay composite plies, could significantly reduce manufacturing costs and, as one could “3D print” topologically optimal designs, improve structural efficiency. In general, topology optimisation integrates well with additive manufacturing. There are, however, two main challenges associated with the adoption of topology optimisation in wind blade design, i.e. accounting for: (i) the aeroelastic response of blades; and (ii) the variety of different materials that would be employed, in the composite laminates as well as the printed structure. To address these challenges, the present paper proposes a new multi-step design and optimisation framework relying on the combination of three software. First, a conventional aero-servo-elastic model is used to evaluate blade loads and displacements. Next, a topology optimisation software is used to optimise the blade laminates and core structure. Third, a lattice generator is used to convert the topological optimised “grey” design into an equivalent cellular design that can be printed using additive manufacturing. The full methodology of this design framework and an initial proof-of-concept topology optimisation solution are presented in this paper.
Effect of blade contamination on power production of wind turbines
Authors: Özgen Serkan , Sarıbel Eda Bahar , Yaman Ali Rıza
Published: June 2022

Wind turbines suffer from considerable power losses because of contamination on their blades, that can be due to erosion, wear, smog, insect, sand and dust particle impact. Blade contamination, its effects on the flows over the wind turbine blades and consequent power production losses form the main focus of the present study. These effects are mainly due to increased roughness on the blades leading to earlier laminar-turbulent transition and consequently, thicker boundary-layers on the blades. Early laminar-turbulent transition leads to a larger part of the flow over a blade being turbulent, thus increasing skin friction drag. Thicker boundary-layer on a blade results in blade profile being effectively modified, rendering the flow over the blade depart from ideal. In the present study, the effects of blade contamination on power output of contaminated wind turbine blades is investigated numerically using an in-house computational tool. Blade Element Momentum Method (BEM) combined with the Panel Method is used to calculate the local velocity and angle of attack at the blade sections, together with the power produced by the blade. Trajectories of particles causing contamination are calculated using Lagrangian approach, also yielding the impingement pattern of the particles on the blade surface, i.e. particle collection efficiency distribution. The effects of roughness on the boundary-layer flow are investigated by using an Integral Boundary-Layer Method, which yields the characteristics of the boundary-layer, i.e. laminar-turbulent transition location, increased skin-friction and thickening of the boundary-layer. The blade shape is modified due contamination thickness, the local height of which is assumed to be proportional to the local collection efficiency. Also, the roughness height distribution used in the boundary-layer calculations is assumed to be equal to the contamination thickness distribution on the blades. Power production and consequent losses of wind turbines with contaminated wind turbine blades are studied with respect to variations in particle size, wind speed and roughness height.
Manufacturing, Testing and Recycling of a small recyclable wind turbine blade
Authors: Carnicero Rafael , Cano Luis , Lopez-Manchado Miguel A , Verdejo Raquel
Published: June 2022

Thermoplastic resins are likely to replace thermoset resins in wind blade manufacturing, as their similar structural properties together with their recyclability would enable the reuse of the raw materials in other composites at the end of life. This paper presents the manufacturing, testing and recycling process of a 1 m thermoplastic composite wind turbine blade compared to a similar thermoset blade. The results showed that the static and centrifugal performance of the two blades were similar, but the thermoplastic composite blade had a lower deflection compared to the epoxy blade. The different components of the thermoplastic blade were recovered by immersion in a suitable solvent for their possible reuse in the manufacture of a new wind turbine blade. Thus, this study provides an example of the use of circular economy principles in a strategic renewable sector, wind energy, validating the use of a new thermoplastic resin in the design and recycling of wind turbine blades, without changing their current manufacturing process.
Aeroelastic model validation of an Active Trailing Edge Flap System tested on a 4.3 MW wind turbine
Authors: Gamberini A , Gomez Gonzalez A , Barlas T
Published: June 2022

Active Trailing Edge Flap Systems (ATEFS) have shown promising results on reducing Wind Turbine fatigue and ultimate loads and increasing the Annual Energy Production. However, the current lack of field validation creates uncertainty in the fidelity level and accuracy of the engineering models used for the aeroelastic modeling of active flaps, and these systems actual load reduction capabilities are in question. This article describes the validation based on field data of the aeroelastic engineering models of the ATEFS developed for the BEM-based solvers HAWC2 and BHawC for the case of stationary activation of the flap. The validation is based on the field test data from a 4.3 MW Wind Turbine with one blade equipped with an ATEFS and operating in normal power production. With simulation results differing from the measurement of a max of ±3% on mean power, ±0.2 deg on mean pitch angle, ±0.1 rpm on rotor speed, and ±2% on flapwise blade loads, the study showed the HAWC2 and BHAWC aeroelastic ATEFS models provide a reliable and precise estimation of the impact of the ATEFS on the Wind Turbine for the case of stationary activation of the flap.
Stall flutter instabilities on the IEA-15 reference wind turbine in idling conditions: code-to-code comparisons and physical analyses
Authors: Loubeyres J. , Pfister J.-L. , Blondel F. , Guy N.
Published: June 2022

The present study investigates stall-induced vibrations on a IEA-15-RWT wind turbine blade. At standstill and under specific strong crosswind conditions, simulations using the codes OpenFAST and DeepLines WindTM exhibit large-amplitude vibrations. Results of both codes are first compared, showing an overall good agreement. Then, the influence of the wind misalignment angle is assessed as well as the choice of aerodynamic polar datasets. Vibrations are observed within two well-marked angular sectors, and the high sensitivity of the phenomenon to the choice of polars is highlighted. Finally, a simplified model based on a spring-mounted aeroelastic section is used to help identifying which type of unstable aeroelastic modes may be at play.
Comparing wind turbine aeroelastic response predictions for turbines with increasingly flexible blades
Authors: Cao Kathy , Shaler Kelsey , Johnson Nick
Published: June 2022

Highly flexible blades are becoming more prevalent designs as a potential solution to the transportation challenges associated with large-scale wind turbine rotors. However, there is currently no quantitative definition of “highly flexible” blades. To further develop turbines with highly flexible blades, a precise definition of the term and accurate simulations of turbines with such blades are required. Assumptions made in the traditional aerodynamic model, Blade Element Momentum (BEM) theory, are violated in turbines with flexible blades. However, Free Vortex Wake (FVW) methods can more accurately model these turbine designs. Though more computationally expensive than BEM, FVW methods are still computationally tractable for use in iterative turbine design. The purpose of this work was to determine the blade flexibility at which BEM and FVW methods begin to produce diverging aeroelastic response results. This was accomplished by simulating the BAR-DRC reference turbine with increasingly flexible blades in a range of steady, uniform inflow conditions using OpenFAST, the National Renewable Energy Laboratory’s physics-based turbine engineering tool. Blade-tip deflections confirmed that BEM and FVW results diverge as blade flexibility increases. For the 212 m rotor diameter turbine used in this study, the two methods largely agreed for smaller blade deflections. But their results differed by an average of 5% when the out-of-plane blade-tip deflections exceeded 5% of the blade length and in-plane blade-tip deflections exceeded 1.25% of the blade length, with percent differences approaching 25% at the largest deflections.
Along-the-path exponential integration for Floquet stability analysis of wind turbines
Authors: Ros J , Olcoz A , Plaza A
Published: June 2022

Traditionally, stability assessment of wind turbines has been performed by eigenanalysis of the azimuthally-averaged linearized system after applying the Multi-Blade Coordinate (MBC) transformation. However, due to internal or external anisotropy, the MBC transform does not produce an exact Linear Time-Invariant (LTI) system, and a Floquet analysis is required to capture the influence of all periodic terms, leading to a more accurate stability analysis. In this paper exponential integration methods that use system linearizations at different blade azimuth positions are used to integrate the perturbed system state and compute the Floquet monodromy matrix. The proposed procedure is assessed for a simple 6 DOF wind turbine model and a more complex aeroelastic model of a 5MW onshore wind turbine. The defined along-the-path or moving-point exponential integrator is found to be the suitable in order to perform a Floquet stability analysis even using a coarse linearization grid.
Comparison of blade optimisation strategies for the IEA 15MW reference turbine
Authors: Scott Samuel , Greaves Peter , Macquart Terence , Pirrera Alberto
Published: June 2022

Reference wind turbine models are crucial for enabling the research community to advance technology and meet the challenges associated with upscaling. The IEA 15 MW is one such reference model, designed using NREL’s WISDEM tool, which enables researchers to perform system-level analysis and optimisation. However, the authors have found the blade to be structurally infeasible when subject to aero-servo-elastic simulations and finite-element (FE) analyses. Given the shortcomings, this work aims to develop an updated blade model for the 15 MW turbine platform using the design tool Aeroelastic Turbine Optimisation Methods (ATOM). Two optimisation processes, with a comprehensive suite of feasibility constraints, are applied: 1) a frozen-loads mass minimisation with fixed planform, and 2) an aero-servo-structural levelised cost of energy (LCoE) minimisation. Results show the frozen-loads optimised design results in a 0.93% increase in LCoE due to the mass penalty of attaining feasibility. In contrast, the aero-structural optimised design results in a 2.29% reduction in LCoE due to mass reductions and increased energy capture—highlighting the benefits of an integrated design process. FE shell analysis of the optimised blades indicates the strength predictions in ATOM are accurate and the main load-bearing spar caps are optimally utilised. Whilst an improvement on the baseline, buckling load factors do not satisfy the target values, indicating the lower fidelity checks in ATOM are non-conservative. The WindIO yaml files for these optimised designs are freely available online.
Accurate Modeling of Material Nonlinearities in a Wind Turbine Spar Cap
Authors: Clarke Ryan J. , Ennis Brandon L. , Miller David A. , Samborsky Daniel D.
Published: June 2022

This study presents component-level testing of carbon fiber sandwich beams and the effect of carbon fiber material nonlinearity in its strain response in bending. A simple material model is presented and validated that accurately captures the carbon fiber longitudinal nonlinearity in both the tensile and compressive response. This material model is implemented in a finite element model of the BAR-DRC reference wind blade, a downwind 100-meter rotor blade, and the effects of the nonlinearity on ultimate limit states of the blade are analyzed. The material nonlinearity has negligible effect on the deflection, and material failure predictions. The buckling analysis revealed significant reductions in buckling load factor in the controlling flap direction caused by the material nonlinearity, revealing the importance of including this material model for buckling analyses of wind blade with carbon fiber reinforced spar caps.
Potential of fibre metal laminates in root joints of wind energy turbine rotor blades
Authors: Petersen E. , Englisch N. , Brand L.-M. , Mahrholz T. , Hühne C.
Published: June 2022

The length of rotor blades is showing continuous growth for future wind energy turbines leading to high bending moments, which must be transferred to the hub by the root section. As the growth of the root diameter is limited by factors such as transportability, motivation to improve the load carrying capacity without changing the geometry is high. Hybridisation with metals shows a possibility to intrinsically increase the bearing strength of fibre-reinforced plastics. This publication presents experimental investigations into hybrid laminates to be used in so-called T-joints for connecting rotor blades to the hub of the nacelle of a wind energy turbine. An overview is given about the bearing strength of several material combinations hybridising glass- and carbon fibre-reinforced plastics (GFRP, CFRP) with aluminium, titanium and steel alloys. A GFRP-steel-hybrid can be identified as a material with a high reinforcing effect even for low amounts of steel. A hybrid T-joint demonstrator is manufactured by resin infusion and tested under static tension. In comparison with a GFRP reference, a joining strength increase of about 33% is achieved for a steel content of 3%. Further coupon level tests reveal a weak spot in the transition zone between the monolithic GFRP region and full hybrid region as the static and fatigue resistance clearly decreases in comparison with monolithic GFRP and full hybrid references.
Comparison of methods for estimating short-term damping of idling wind turbine modes from measurements
Authors: Ebbehøj K L , Couturier P , Orlowitz E , Høgsberg J , Thomsen J J
Published: June 2022

Three methods for estimating time-varying (Hilbert-Huang transform, continuous wavelet transformation and partial Floquet analysis) and one for time-invariant (stochastic subspace identification) natural frequencies and viscous damping ratios based on free responses are tested and compared. The methods’ performance and sensitivities to several system characteristics are tested with a series of simulated responses. It is shown that, of the group of three methods, partial Floquet is the most suitable and Hilbert-Huang transform is unsuitable for the responses tested. Of the four methods tested, the stochastic subspace identification method is shown to be the method most robust to measurement noise, but its estimates contain notable bias error due to the short time series used. Natural frequencies and damping ratios of four edgewise blade modes are estimated based on measured responses from a single output location. The median of the estimated damping for these four modes have been calculated to be almost the same.
Analysis and Validation of Glauert Rotor Design
Authors: Sørensen Jens N. , Ramos-García Néstor , Okulov Valéry L.
Published: June 2022

The design of industrial wind turbine rotors is generally based on the blade-element/momentum (BEM) approach introduced by Glauert (1935). Essentially, the theory consists of combining a blade-element approach with axial momentum theory, and then introducing a tip correction to account for the finite number of rotor blades. This is required, as the momentum theory is based on representing the rotor by a disk, corresponding to a rotor with infinitely many blades. The optimum design properties are obtained by optimizing the local power coefficient at each blade element. This is typically accomplished by solving a simple analytical system of equations for the axial and tangential inductions factors, ignoring at first the tip correction. The tip correction is subsequently introduced to correct the design variables. In the present work we analyse the implications of including the tip correction directly in the optimization. As a result of the analysis, we find the somewhat surprising result that the maximum optimal interference factor is not 1/3, as normally encountered for optimum rotor design, but 2/5. In the paper we prove this analytically and use the theory to design optimum rotors, which subsequently are benchmarked by comparison to results from a numerical lifting line model.
Operations expenditure modelling of the X-Rotor offshore wind turbine concept
Authors: Flannigan Callum , Carroll James , Leithead William
Published: June 2022

O&M of an offshore wind farm is becoming increasingly challenging as farms are being commissioned further from shore. Weather windows are more difficult to navigate leading to longer downtime for turbines. The X-Rotor offshore wind turbine concept directly tackles these O&M challenges by, amongst other advantages, removing the requirements for components that have traditionally contributed high failure rates, repair times and downtimes, and by placing the heavy and expensive machinery closer to sea level. The turbine also benefits from having modular small rotors that can be quickly replaced and repaired onshore, and being able to operate at reduced capacity when there are failures in the modular rotors. This paper presents the StrathX-OM OpEx model. This model features changes to OpEx modelling that will allow for comprehensive analysis of the operations and maintenance costs for a wind farm made up of radical X-Rotor wind turbines with the flexibility to handle changing designs as the technology progresses. The calculation of lifetime O&M costs for a wind farm 100 km from shore showed that the X-Rotor has lower O&M costs than conventional HAWTs for an established design. A sensitivity study on the estimated failure rates of X-Rotor is also presented. This shows that even with significantly over-estimated failure rates the X-Rotor would still be competitive in today’s market.
Comparison of aerodynamic planform optimization of non-planar rotors using blade element momentum method and a vortex cylinder model
Authors: Li Ang , Gaunaa Mac , Lønbæk Kenneth , Zahle Frederik , Pirrung Georg Raimund
Published: June 2022

The present work compares non-planar rotors designed using the blade element momentum (BEM) method and a vortex cylinder model. In a previous work, it is shown that blade element theory coupled with the superposition of the vortex cylinder model (BEVC) is able to model the loads of non-planar rotors. The result predicted by the BEVC model is in significantly improved agreement with higher-fidelity models than the loads as predicted using the BEM method. In this work, the BEM method and the BEVC method are integrated into a gradient-based optimization framework for aerodynamic planform optimization, in which the analytical gradients are obtained using the algorithmic differentiation (AD) method. In the present study, the rotor is assumed to be stiff for all cases such that the pure aerodynamic effects are highlighted. Loads of the optimized non-planar rotors with different geometries under different constraints designed from both methods are calculated using the BEM method, the BEVC method and also the higher-fidelity lifting-line (LL) method. Within the constraints of the present work it was found that the advantage of the BEVC method is not significant when comparing the integrated aerodynamic loads: the non-planar rotor designed using the BEM method gives similar total thrust and power as the rotor designed using the BEVC method when the designs are evaluated with the higher-fidelity LL method. However, the results confirmed that the distributed aerodynamic loads of the non-planar rotors predicted by the BEVC method are in improved agreement with the LL method compared to the BEM method.
Study of a passive pitching rotor using blade element momentum theory coupled to a rigid-body model
Authors: Krishnan Navaneetha , Viré Axelle , Klippe Rikus van de
Published: June 2022

Misaligned wind turbine rotors experience uneven loads because of two effects: dissymmetry of lift, and skewed wake effect. Rotor-crafts that have a similar problem introduce various mechanisms to combat this — one of them is to add a δ3-hinge. The hinge provides the blade with an additional degree of freedom to relieve the unbalanced loads; in theory, it is a self-correcting mechanism. In this work, we couple a blade element momentum (BEM) approach for the aerodynamics to a rigid-body model that simulates the hinge rotation. The results from BEM are used to identify the working mechanisms of the hinged rotor and highlight the strengths and weaknesses of such a rotor.
Aeroelastic model validation with 8 MW field measurements: Influence of constrained turbulence with focus on power performance
Authors: Huhn Matthias L. , Gómez-Mejía Andrés F.
Published: June 2022

Aeroelastic model simulations are essential for the design of wind turbines. Validation of these models is important to have confidence in the results of the models. It is a challenge to ensure that the input for the simulations, that is the wind field, corresponds as closely as possible to the real conditions during the measurement. We present the latest results of a validation campaign at an 8 MW wind turbine. We investigate the appropriateness of TurbSim’s constrained turbulence model TIMESR for model validation and compare the validation results with the Kaimal turbulence model with a focus on power performance. TIMESR wind resulted in a slightly lower power performance in the part-load region than Kaimal wind. In contrast, the rotor speed showed a good agreement with measurements both using TIMESR wind as well as using Kaimal wind. Additionally, the linear regression result implies that the constrained turbulence wind field enables the model to reproduce a specific 10 min measurement. However, up to know the simulations show a consistently lower power in the part load region, which might result from a systematic error in the validation chain.
Potential of damage accumulation during segmented rotor blade fatigue tests
Authors: Melcher David , Petersen Enno , McInnes Matthew
Published: June 2022

Modern wind turbines have higher rated power and improved capacity factors. This results in very long and slender blades which are also designed closer to the material limits. As a consequence, blade test facilities need to be upgraded for static and fatigue full-scale blade testing to carry larger loads and deal with larger tip deflections. Another aspect is the adaption of the test methods to avoid high overloads, which can cause premature damage and require time-consuming repairs. One drawback of traditional full-scale tests with a full-length rotor blade is the long time needed for certification as the blades have low eigenfrequencies and hence high fatigue test durations. This work presents an alternative fatigue testing approach for rotor blades which combines full-length and segmented fatigue tests, each contributing to the accumulated fatigue damage. The proposed approach is benchmarked with the traditional approach by means of a numerical optimization study. applying this approach to a current offshore rotor blade design illustrates the potential for reducing the fatigue test duration by 66% and the local fatigue damage overload to a mere fraction.
Fatigue damage calculation of offshore wind turbines’ long-term data considering the low-frequency fatigue dynamics
Authors: Sadeghi Negin , Robbelein Koen , D’Antuono Pietro , Noppe Nymfa , Weijtjens Wout , Devriendt Christof
Published: June 2022

The mutual and simultaneous action of external variable forces on (offshore) wind support structures causes fatigue. Fatigue analysis in this context relies on 10-minute-long strain signals. Cycle-counting allows capturing the fatigue cycles nested within these signals but inevitably leaves some open loops called half-cycles or residuals. Some other loops are not even cycle-counted because the algorithm cannot catch low-frequency (LF) cycles spanning more than 10 minutes, as caused, e.g., by wind speed variations. Notwithstanding, LF cycles are also the most damaging since they always contain the highest range in the variable amplitude signal. Therefore, counting multiple 10-minute signals and merging the resulting histograms into one inevitably has some non-conservative effects, for it leaves the LF cycles uncounted. In this work, we avoid signal concatenation to recover the LF effect. To do so, we use the residuals sequence from the 10-minute signals as it embeds the LF information. As method validation, we compare the impact of LF fatigue dynamics recovery on the linearly accumulated damage using a real-life dataset measured at a Belgian offshore wind turbine. By defining a factor that incorporates the LF effect, we observe that after 300 days of observation, the factor converges to a fixed value.
Wind turbine gearbox fault prognosis using high-frequency SCADA data
Authors: Verma Ayush , Zappalá Donatella , Sheng Shawn , Watson Simon J.
Published: June 2022

Condition-based maintenance using routinely collected Supervisory Control and Data Acquisition (SCADA) data is a promising strategy to reduce downtime and costs associated with wind farm operations and maintenance. New approaches are continuously being developed to improve the condition monitoring for wind turbines. Development of normal behaviour models is a popular approach in studies using SCADA data. This paper first presents a data-driven framework to apply normal behaviour models using an artificial neural network approach for wind turbine gearbox prognostics. A one-class support vector machine classifier, combining different error parameters, is used to analyse the normal behaviour model error to develop a robust threshold to distinguish anomalous wind turbine operation. A detailed sensitivity study is then conducted to evaluate the potential of using high-frequency SCADA data for wind turbine gearbox prognostics. The results based on operational data from one wind turbine show that, compared to the conventionally used 10-min averaged SCADA data, the use of high-frequency data is valuable as it leads to improved prognostic predictions. High-frequency data provides more insights into the dynamics of the condition of the wind turbine components and can aid in earlier detection of faults.
Data-driven state estimation toward blade individual load-reduction of wind turbines1
Authors: Klein A , Konrad T , Abel D
Published: June 2022

As wind turbines tend to be build larger every year, the importance of load-reducing controls to damp the rotor blade oscillations increases. For a control algorithm to perform blade individual load-reducing strategies, online information about each rotor blade’s deflection is needed. An approach for wind turbine state estimation with special attention to the rotor blade deflections is given using a Hammerstein model driven by simulation data in a Kalman Filter (KF). The Hammerstein’s linear submodel is mainly derived as time discrete state space system via least squares, while nonlinear effects are defined in terms of their proportionality. The model noise definition required by the KF is calculated by the system model’s one-step prediction error. The simulation results show the estimate to have a standard deviation of less than 2 % in edge and 9% in flap-wise direction when using an appropriate sensor configuration. Using state-of-the-art sensors, standard deviations of less than 4% and 25% respectively are achieved. The approach is particularly attractive due to the low level of tuning required. The usage of the state estimation in a closed control loop as well as the Hammerstein model in a model-based control system offer room for promising further investigations.