Full-scale Wind Turbine Research Articles

Extended scaling approach for droplet flow and glaze ice accretion on a rotating wind turbine blade

This paper presents and analyzes a non-dimensional model of the flow field and droplet trajectories with glaze ice accretion on a rotating wind turbine blade. The formulation leads to similitude relationships for glaze ice accretion to evaluate new scaling parameters corresponding to the rotation of the blade. New scaling parameters are developed to determine ice scaling conditions based on the geometry scale factor of a wind turbine blade. The scaling methodology can be used to determine alternative test conditions and predict glaze icing conditions on a full-scale wind turbine blade. Numerical CFD icing simulations are performed using ANSYS FENSAP ICE software. A wind blade model is developed using blade element momentum theory (BEM). Each blade size is tested at specific flow conditions using the scaling equations. Scaled conditions for velocity (streamwise and rotational), droplet size, and icing time are tested. CFD solutions for the flow field are obtained for comparisons of the velocity, droplet trajectories, pressure coefficient distributions, ice thickness, and ice shapes. Recommended parameters to be used for glaze ice scaling on a rotating blade are presented and numerical results are reported to support these recommendations. The paper provides new insights into modeling of glaze ice accretion on large wind turbine blades based on smaller scaled blade sections tested in a laboratory setting.

Experimental and two-scale numerical studies on the behavior of prestressed concrete-steel hybrid wind turbine tower models

Prestressed concrete-steel hybrid (PCSH) wind turbine tower has been recognized as an efficient alternative to traditional steel tube supporting towers for wind farms in harsh sites such as mountain regions. To investigate the global and local mechanical behavior including failure patterns of a full scale PCSH wind turbine towers, an experimental study on a substructure of a scaled PCSH tower is carried out firstly. Then, a material subroutine for three-dimensional (3D) fiber beam elements suitable for implicit analysis on the mechanical behavior of the substructure of the scaled PCSH tower is developed. A two-scale numerical model of the substructure of the scaled PCSH wind turbine tower employing the developed 3D fiber beam elements and solid elements is developed. The accuracy and efficiency of the developed two-scale numerical model for the behavior simulation of the substructure of the scaled PCSH wind turbine tower is illustrated by comparing the numerical results with the experimental measurements. Additional comparison of the simulation results using the developed two-scale numerical model is made with them of a model using sole 3D fiber beam elements and a model using sole solid elements, respectively. Results show that the force–displacement curve determined with the developed two-scale model is close to the test result and coincident well with that of the two models using 3D fiber beam elements and the solid elements. The developed two-scale model can describe the global behavior, the local failure patterns and the stress distribution of the tested specimen accurately with improved simulation efficiency. Finally, the validated two-scale modelling approach is employed to analyze the static behavior, modal parameter, and fatigue of the optimized full-scale PCSH wind turbine tower previously developed by the authors. The simulation results show that the two-scale model can reflect the stress of the PCSH wind turbine tower at the critical position as well as the global mechanical behavior with higher computational efficiency. The fiber beam model can be used for predicting only global, but not local, behavior.

Wind Tunnel Tests of Wake Characteristics for a Scaled Wind Turbine Model Based on Dynamic Similarity

This wind tunnel study was conducted to investigate the similarity laws involved in the reasonable simulation of the wake characteristics of a full-scale wind turbine. A 5 MW scaled wind turbine model was designed using an optimization method based on the blade element momentum (BEM) theory. Subsequently, wind tunnel tests were carried out on the geometrically similar model and the thrust-optimized model, with different yaw angles and under various upstream flow conditions. The results indicated that the wake development of the wind turbine model was closely related to the thrust forces of the wind turbine, and both kinematic and dynamic similarity laws should be observed to achieve wake characteristics that are reasonably similar to those of a full-scale wind turbine. This study investigated the aerodynamic similarity principles of small-scale wind turbine models to develop a more effective method for simulating full-scale turbine wake characteristics in wind tunnel tests. The outcomes of this study revealed the limitations of the anomalously low thrust coefficients in geometrically similar wind turbine models and present reasonable model design methodologies for small-scale wind turbine models in wind tunnel tests.

Improved resonance method for fatigue test of full-scale wind turbine blades

To further reduce the power of exciter in the common fatigue testing methods and increase the testing frequency to decrease the fatigue testing time, this paper proposes an improved fatigue testing method—Tug Fatigue Testing system (TFTs). The advantages of this new fatigue testing method are low power and high testing frequency of its exciter due to no exciter with moving masses attached to the blade. In TFTs, exciters mounted on the ground or fixed bracket can be used to excite the blade in the uniaxial or biaxial fatigue test. In this paper, the mechanical model of TFTs is established to compare the motor power required by exciters in TFTs and the inertial exciters and the shear load on the blades in both ways. Furthermore, a test of a 56.5 m blade will be performed to verify the feasibility of the new method. In addition, the bending moment distribution of an 80 m blade excited by TFTs was measured and compared with the bending moment distribution of the same blade excited by inertial resonance excitation to evaluate its excitation effect. The test results prove that this improved method needs lower power of exciter, produces smaller shear loads, and provides a higher test frequency in the flap-wise test direction than common inertial resonance excitation. Biaxial fatigue tests can also be conducted by this new method.

On the Investigation of the Effect of Tower and Hub Exclusion on the Numerical Results of a Horizontal Axis Wind Turbine

In order to construct a 3D rotor model, periodicity and Multiple Reference Frame (MRF) strategies were applied to address full Computational Fluid Dynamics (CFD) that incorporate the Reynolds-averaged Navier–Stokes (RANS) equations. A simulation model was run to examine the power of the wind turbines, both including and excluding the hub and tower. The purpose of this was to identify an approach that would decrease the computational time cost of wind turbine simulation. Firstly, a full-scale horizontal axis wind turbine simulation was carried out, and subsequently, comparisons were made with the results of the wind tunnel experiment utilizing the K-omega SST and Sparlat Allmaras viscosity models. The results were compared to determine the optimum model with the lowest simulation time and highest accuracy to the experimental results. Following this, the complete models’ simulation was compared to the model excluding the hub and tower in order to check the disparity in the results of the two. Additionally, to ascertain the computational cost saving, the ratio of the two simulation times was established. The findings show that the two models produce results that correspond well to the experimental results, and that the power coefficient had a greater value for the complete model than the simple model. Furthermore, it was found that the power coefficient values of the full model have significantly higher levels of similarity to the experimental values. The Sparlat Allmaras and K-omega SST viscosity models returned error percentages of 0.52% and 12.6% respectively. For the partial model utilizing the same computer device, a 5.7% error rate was recorded, with a computational time saving of approximately 34%.

Evaluation of dynamic testing of full-scale wind turbine drivetrains with hardware-in-the-loop

Dynamometer testing of full-scale wind turbine drivetrains involves subjecting integrated components to extreme static loads, fatigue loads, or dynamic loads to replicate field conditions. This paper provides a detailed evaluation of the uncertainty and errors in applied loads and measured responses, and their magnitude relative to established repeatability bounds for a drivetrain subjected to static and dynamic loads on the 7.5 MW test bench at the Clemson University Wind Turbine Drivetrain Testing Facility. An ideal drivetrain simulation model is utilized to isolate the influence of load tracking errors on test article responses. It is shown that the test article response variations are mainly driven by run out and clearances inherent to the drivetrain. For the dynamic profiles, the load tracking errors are within acceptable limits. A frequency analysis is used to show that the test bench controller tracking performance is acceptable for profiles with frequency content up to 1.5 Hz.

Thermographic data analytics-based damage characterization in a large-scale composite structure under cyclic loading

Large-scale composite structures such as aircraft wings and wind turbine blades undergo cyclic loading in operation. In-service damage often generates excessive heat due to material frictions and it could be detected by thermography. This study develops a methodology to quantitatively analyze such structural damage based on thermographic data analytics. A full-scale composite wind turbine blade is inspected using passive thermography when it is subject to cyclic loads in laboratory. The damage region is identified from thermographic images and it is tracked automatically using image processing. The damage region is subsequently characterized on both overall and detailed levels. The change of the damage status versus fatigue cycle number is analyzed and the information regarding the growth of the damage area and the damage severity is provided. The initiation and the progress of damage are investigated based on the temperature and the enthalpy change in the damage region. This study provides a viable solution for efficient structural health monitoring and damage prognosis of large-scale composite structures under cyclic loading.

Modal analysis of full-scale wind turbine blade structural fatigue tests based on particle swarm optimization

Abstract Modal analysis is the vital prerequisite of the full-scale fatigue test of the wind turbine blade. In order to resolve the difficulty in solving the characteristic equation of the transfer matrix method in modal analysis, a method of solving the characteristic equation based on particle swarm optimization is proposed. Firstly, the beam model is used to simplify and discrete the blade along the spanwise of the blade. A concept of average bending stiffness is used for the elasticity assignment with beam segment, and the blade kinematics model is established. Subsequently, a designed particle swarm optimization is used to solve the characteristic equation. Finally, the proposed method is verified by modal analysis of an MW-scale blade. On this basis, the effect of the mass and position of the counterweight on the mode shape is investigated. The results indicate that the proposed method can provide a theoretical reference for the fatigue test technology of wind turbine blades.

Research on negative sequence current coordinated control strategy for severe asymmetric offshore ac faults of wind power transmission system based on mmchvdc

When there is a severe asymmetric offshore ac fault in the grid-connected system for full-scale type-4 wind turbines via the high voltage direct current (HVDC) transmission system based on modular multilevel converters (MMC), there will be transient overcurrent in the MMC and the grid side converters (GSC) of wind turbines. In order to prevent transient overcurrent, a negative sequence coordinated current control strategy is proposed in this paper. The method of decoupling circuit characteristics and control characteristics is adopted to study the asymmetric fault characteristics of this system. The levels of the negative sequence current during severe asymmetric ac faults are analysed. The key influencing factor of the negative sequence currents is extracted. And the feature that the negative sequence currents of the MMC and the GSC cannot be suppressed to 0 simultaneously is revealed. Based on the above reasons, the control strategy that the negative sequence current of the MMC is suppressed to zero and the GSC cooperate to reduce the positive sequence current thus reducing the current stress of the bridge arm is proposed. Finally, an electromagnetic transient model was built on PSCAD to verify the effectiveness of the control strategy.

Parametric Analysis Using CFD to Study the Impact of Geometric and Numerical Modeling on the Performance of a Small Scale Horizontal Axis Wind Turbine

The reliance on Computational Fluid Dynamics (CFD) simulations has drastically increased over time to evaluate the aerodynamic performance of small-scale wind turbines. With the rapid variability in customer demand, industrial requirements, economic constraints, and time limitations associated with the design and development of small-scale wind turbines, the trade-off between computational resources and the simulation’s numerical accuracy may vary significantly. In the context of wind turbine design and analysis, high fidelity simulation under full geometric and numerical complexity is more accurate but pose significant demands from a computational standpoint. There is a need to understand and quantify performance deterioration of high fidelity simulations under reduced geometric or numerical approximation on a single small scale turbine model. In the present work, the flow past a small-scale Horizontal Axis Wind Turbine (HAWT) was simulated under various geometric and numerical configurations. The geometric complexity was varied based on stationary and rotating turbine conditions. In the stationary case, simple 2D airfoil, 2.5D blade, 3D blade sections are evaluated, while rotational effects are introduced for the configuration 3D blade, rotor only, and the full-scale wind turbine with and without the inclusion of a nacelle and tower. In terms of numerical complexity, the Single Reference Frame (SRF), Multiple Reference Frames (MRF), and the Sliding Meshing Interface (SMI) is analyzed over Tip Speed Ratios (TSR) of 3, 6, 10. The quantification of aerodynamic coefficients of the blade (Cl, Cd) and turbine (Cp, Ct) was conducted along with the discussion on wake patterns in comparison with experimental data.

Performance simulation of wind turbine with optimal designed trailing-edge serrations

Trailing-edge (TE) serration is a widely used instrument for noise control on wind turbine blades. Most of previous studies on TE serrations focused on noise reduction, but its aerodynamic effects on wind turbine performance have not received much attention yet. In this study, effects of serrations on the performance of a 2.3 MW wind turbine, including the power output and load characteristics, are examined using the airfoil analysis tool Rfoil and wind turbine analysis code Bladed. An optimal design method setting maximum power output as the design object is applied to determine the configurations of serrations regarding the airfoils corresponding to two sections in the last 20% span. Compared with the baseline airfoils, the serrated airfoils have higher lift-to-drag ratio at the angle of attack under the rated wind speed. For a full-scale wind turbine, the presence of serrations can slightly increase the static electrical power and the load at the blade root before the rated wind speed is achieved, and consequently increase the annual power output by less than 0.7%. However, under the turbulence wind conditions, the serrated blade has larger mean and maximum moment at the root and stronger load fluctuation, since the presence of serrations increases the angular moment of the airfoil. The analysis results suggest that using optimal designed TE serrations can achieve reduction of noise and increase of power output simultaneously, at the cost of increase of blade load.

Extensive model validation for generic IEC 61400-27-1 wind turbine models

The aim of this paper is to demonstrate the usefulness, practical applicability, accuracy and reliability of Standard IEC 61400-27-1. The objective of this standard is to specify generic simulation models for the four main types of wind turbines, as well as procedures to validate them. Given that most of the works published and related to the validation of generic wind turbine models have applied a limited number of voltage dip tests to a single wind turbine, the present paper significantly widens the scope of these studies, conducting a total of 59 voltage dip field tests in 7 different wind turbines from 3 manufacturers. The Type 3 and Type 4 wind turbines, i.e., the doubly-fed and the full-scale converter wind turbines, respectively, are the two topologies analysed, since these comprise the vast majority of the market share for new wind turbines. The field measurements carried out on the actual wind turbines are compared to the simulation results of the corresponding IEC dynamic wind turbine models, and the IEC validation methodology is applied. Based on the results obtained, several comparative analyses are performed, and the reasons for differences in the accuracy of the behaviour of the wind turbine topologies considered are also analysed.

How realistic are the wakes of scaled wind turbine models?

Abstract. The aim of this paper is to analyze to which extent wind tunnel experiments can represent the behavior of full-scale wind turbine wakes. The question is relevant because on the one hand scaled models are extensively used for wake and farm control studies, whereas on the other hand not all wake-relevant physical characteristics of a full-scale turbine can be exactly matched by a scaled model. In particular, a detailed scaling analysis reveals that the scaled model accurately represents the principal physical phenomena taking place in the outer shell of the near wake, whereas differences exist in its inner core. A large-eddy simulation actuator-line method is first validated with respect to wind tunnel measurements and then used to perform a thorough comparison of the wake at the two scales. It is concluded that, notwithstanding the existence of some mismatched effects, the scaled wake is remarkably similar to the full-scale one, except in the immediate proximity of the rotor.

A novel solution for preventing leading edge erosion in wind turbine blades

ABSTRACT Over the past 30 years, wind energy has been established as one of the leading forms of renewable energy. As the industry grows so too does the size of the wind turbines themselves – large wind turbines can now generate up to 15 MW. However, with larger turbines comes additional structural challenges to overcome, where one such challenge is erosion along the leading edge of the blade due to water impingement at the higher tip speeds of the blade. Therefore, in this paper, the development of a novel solution for preventing leading edge erosion on wind turbine blades (LEP) is presented. Primarily, this paper describes the experimental testing campaigns that were performed during LEP development. Based on the results from the rain erosion testing of selected materials, their manufacturability and other mechanical properties, thermoplastic polyurethane has been selected as the most suitable material to manufacture the LEP. The LEP component was de-risked through demonstrator testing and then bonded to the leading edge of a full-scale wind turbine blade. Structural (dynamic, static and fatigue mechanical) testing was performed on the blade with no significant damage observed. The next stage of development is operational trials on a wind turbine in marine conditions.

Investigation and Validation of Numerical Models for Composite Wind Turbine Blades

As the world shifts to using renewable sources of energy, wind energy has been established as one of the leading forms of renewable energy. As the requirement for wind energy increases, so too does the size of the turbines themselves, where the latest turbines are 10 MW with a turbine diameter in excess of 190 m. The design and manufacture of the blades for these turbines will be critical if they are to last for the design life, where the accuracy of the numerical models used in the design process is paramount. Therefore, in this paper, three independent numerical models have been created using three available finite element method packages—ABAQUS, ANSYS, and CalculiX—and the results were compiled. Following this, the accuracy of the models has been evaluated and validated against the results from an experimental testing campaign. In order to complete the study, a 13 m full-scale wind turbine blade has been used, which has been subjected to static testing in both the edgewise and flapwise directions. The results from this testing campaign, along with the blade mass and natural frequencies, have been compared to the results from the independent numerical models. The differences in the models, along with other sources of error, have been discussed, which includes recommendations on the development of accurate numerical models.

Considerations for testing full-scale wind turbine nacelles with hardware-in-the-loop

In this paper, pole placement control techniques are utilized to compensate for variations in the torsional dynamics resulting from the different boundary conditions experienced by a wind turbine nacelle when mounted on a test bench. Simulation case studies are used to understand the baseline torsional characteristics of the nacelle coupled to the test bench versus that coupled to the rotor. It was found that the frequency shifts by up to 200% and 400% for the first and second torsional modes, respectively. The feasibility of utilizing pole placement technique to match the torsional characteristics of the turbine on the test bench is investigated using PI and PID controllers. The performance of the tuned controller is then verified under two test scenarios: Low Voltage Ride Through (LVRT), and a highly dynamic turbulent wind input. It is demonstrated that tuning the test bench speed controller can effectively shift the poles of the closed-loop system to match the desired first and second modes of the full turbine and replicate transient field events on the test bench.

Near-wake structure of full-scale vertical-axis wind turbines

Abstract

State-of-the-art investigation of wind turbine structures founded on soft clay by considering the soil-foundation-structure interaction phenomenon – Optimization of battered RC piles

Nonlinear dynamic modelling of full-scale wind turbine structures and soil-structure interaction considerations using the 3D detailed approach is the most accurate method of investigating the mechanical response of these structures, but not yet feasible due to numerous reasons. The two main numerical problems that do not allow for this type of analysis to be performed, are the numerical instabilities that immerse during the dynamic analysis and the excessive computational demand. This work will present the computational response of a newly developed algorithm that is used herein to perform modal analysis of wind turbine structures for the investigation of soil-foundation-structure interaction phenomenon. An extensive numerical investigation is presented that foresees the performance of modal and pushover analysis on a wind turbine structure that has an 80 m steel tower and is founded on different soil profiles. The 3D detailed models constructed herein consider the effect of soil-foundation-structure interaction by discretizing for the first time the superstructure, pile foundation and soil domains through 8-noded hexahedral elements, achieving maximum modelling accuracy. The soil material properties used in this research work derived from an onsite geotechnical investigation performed for the needs of the WindAfrica project. After validating the ability of the proposed modelling approach to capture the mechanical behaviour of reinforced concrete foundations through the use of experimental data found in the international literature, the optimum inclination of battered piles was studied through an excessive numerical parametric investigation. Based on the numerical findings, the optimum inclination of the battered piles was that of 10 degrees, where the failure of the wind turbine structure was found to be located at the base of the steel tower due to local buckling.

Field test of an active flap system on a full-scale wind turbine

Abstract. This article describes a series of validation tests of an active flap system (AFS) on a multi-megawatt wind turbine. A single blade of a 4 MW turbine with 130 m rotor diameter (SWT-4.0-130) is retrofitted in the outer 15–20 m with the AFS. The AFS is controlled remotely with a pneumatic pressure supply system located in the hub of the turbine. The measurements were performed between October 2017 and June 2019 using two different AFS configurations on the blade. A description of the system setup is given, as well as comparisons of measurements and aeroelastic simulations. The measurements quantify the static load control authority of the AFS in atmospheric conditions, providing a preliminary estimate of load impact potential for the concept. This article presents, furthermore, a new method for the characterization of the load impact of such a system and its dynamic response under atmospheric conditions based on a blade-to-blade load comparison.

Development of a numerical model of a novel leading edge protection component for wind turbine blades

Abstract. As the world shifts to using renewable sources of energy, wind energy has been established as one of the leading forms of renewable energy. However, as wind turbines get increasingly larger, new challenges within the design, manufacture and operation of the turbine are presented. One such challenge is leading edge erosion on wind turbine blades. With larger wind turbine blades, tip speeds begin to reach over 300 km h−1. As water droplets impact along the leading edge of the blade, rain erosion begins to occur, increasing maintenance costs and reducing the design life of the blade. In response to this, a new leading edge protection component (LEP) for offshore for wind turbine blades is being developed, which is manufactured from thermoplastic polyurethane. In this paper, an advanced finite element analysis (FEA) model of this new leading edge protection component has been developed. Within this study, the FEA model has been validated against experimental trials at demonstrator level, comparing the deflection and strains during testing, and was found to be in good agreement. The model is then applied to a full-scale wind turbine blade and is then modelled with the LEP bonded onto the blade's leading edge and compared to previously performed experimental trials, where the results were found to be well aligned when comparing the deflections of the blade. The methodology used to develop the FEA model can be applied to other wind blade designs in order to incorporate the new leading edge protection component to eliminate the risk of rain erosion and improve the sustainability of wind turbine blade manufacture while increasing the service life of the blade.