bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of blade contamination on power production of wind turbines
Authors: Özgen Serkan , Sarıbel Eda Bahar , Yaman Ali Rıza 
Published: June 2022

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

AbstractThis 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

AbstractMisaligned 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

Abstract
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

Abstract
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.