Full-scale Wind Research Articles

Investigation of the Effect of Tire Deformation on Open-Wheel Aerodynamics

<div class="section abstract"><div class="htmlview paragraph">This paper introduces a finite element (FE) approach to determine tire deformation and its effect on open-wheeled racecar aerodynamics. In recent literature tire deformation was measured optically. Combined loads like accelerating at corner exit are difficult to reproduce in wind tunnels and requires several optical devices to measure the tire deformation. In contrast, an FE approach is capable of determining the tire deformation in combined load states accurately. The FE tire model was validated using computer tomography images, 3D scan measurements, contact patch measurements and stiffness measurements. The deformed shape of the FE model was used in a computational fluid dynamics (CFD) simulation. A sensitivity study was created to determine the effect of the tire deformation on aerodynamics for unloaded and loaded tires. In addition, the influence of these tire deformations was investigated in a CFD study using a full vehicle model. The CFD model was validated through full scale wind tunnel tests as well as on-road tests. Finally, a straight-line and a steady state cornering maneuver based on a vehicle dynamics simulation were simulated using this combined approach of FE and CFD. The tire deformation included proper wheel load, wheel speed and slip angle for each wheel. The CFD full vehicle model took chassis slip angle, body roll angle and wheel steering angle into account in order to match the real driving situation. The results show that realistic tire deformations provide better insight into the effect of rotating wheels on aerodynamics of full vehicles, especially that of race cars.</div></div>

Power control strategies for grid connected converters applied to full-scale wind energy conversion systems during LVRT operation

Some grid codes establish that during voltage sags, the generation units employing static converters must favor the electrical mains support. Unbalanced voltage sags generate grid power oscillations with twice the fundamental frequency. This way, the converter control can be modified to mitigate the unbalanced sag effects to the grid converter. The present work analyzes different power control methods presented in literature, in order to study how they affect the active and reactive power oscillation and the generated current waveform. A case study with a simulation of a 2(MW) WECS is performed in order to analyze the strategies behavior in terms of power fluctuation and converter dc bus impacts. It is evaluated the system behavior over different operation points of reactive current injection curve, defined in the modern grid codes.

Experimental validation and improvement of actuator line model in the large-eddy simulation of wind-turbine wakes

Wind-turbine wakes significantly affect the power output of downstream wind turbines. In order to improve the calculation accuracy of wind-turbine wakes in the atmospheric boundary layer, a new improved actuator line - large-eddy simulation (AL-LES) method is proposed and verified by experiments. The traditional AL-LES method is improved in three aspects. Firstly, the atmospheric turbulence is generated by a dynamic k-equation LES with a wall shear stress model and a buoyancy effect model. Secondly, the nacelle and tower are modelled based on the static actuator line method. Finally, the distribution of blade body force is improved by using an anisotropic 3D Gaussian function. Based on the results of three wind tunnel experiments conducted by Norwegian University of Science and Technology (NTNU), China Aerodynamics Research and Development Centre (CARDC) and Von Karman Institute for Fluid Dynamics (VKI), the improved AL-LES method is validated from the aspects of wind-turbine power performance, the generation of tip vortex, and the distribution of wake velocity under typical offshore and onshore conditions. In addition, a full-scale wind turbine installed in Gansu is used for the experimental and numerical research. The main conclusion is that compared with the traditional method, the new AL-LES method improves the numerical accuracy by nearly 22%, and can more accurately simulate the interaction between atmospheric turbulence and wind-turbine wakes. The results can help the research of wind-turbine wakes and the micro-location selection of wind farm.

An experimental investigation into passive acoustic damage detection for structural health monitoring of wind turbine blades

This article details the implementation of a novel passive structural health monitoring approach for damage detection in wind turbine blades using airborne sound. The approach utilizes blade-internal microphones to detect trends, shifts, or spikes in the sound pressure level of the blade cavity using a limited network of internally distributed airborne acoustic sensors, naturally occurring passive system excitation, and periodic measurement windows. A test campaign was performed on a utility-scale wind turbine blade undergoing fatigue testing to demonstrate the ability of the method for structural health monitoring applications. The preliminary audio signal processing steps used in the study, which were heavily influenced by those methods commonly utilized in speech-processing applications, are discussed in detail. Principal component analysis and K-means clustering are applied to the feature-space representation of the data set to identify any outliers (synonymous with deviations from the normal operation of the wind turbine blade) in the measurements. The performance of the system is evaluated based on its ability to detect those structural events in the blade that are identified by making manual observations of the measurements. The signal processing methods proposed within the article are shown to be successful in detecting structural and acoustic aberrations experienced by a full-scale wind turbine blade undergoing fatigue testing. Following the assessment of the data, recommendations are given to address the future development of the approach in terms of physical limitations, signal processing techniques, and machine learning options.

FAPI Controller for Frequency Support in Low-Inertia Power Systems

This paper presents different forms of Fast Active Power Injection (FAPI) control schemes for the analysis and development of different mitigation measures to address the frequency stability problem due to the growth of the penetration level of the Power Electronic Interfaced Generation (PEIG) in sustainable interconnected energy systems. Among the studied FAPI control schemes, two different approaches in the form of a derivative-based control and a virtual synchronous power (VSP) based control for wind turbine applications are also proposed. All schemes are attached to the PEIG represented by a generic model of wind turbines type 4. The derivative-based FAPI control is applied as an extension of the droop based control scheme, which is dependent on the measurement of the network frequency. By contrast, the proposed VSP-based FAPI is fed by the measurement of the active power deviation. Additionally, unlike existing approaches for virtual synchronous machines, which are characterized by high-order transfer functions, the proposed VSP-based FAPI is defined by a second-order transfer function, which can contribute to fast mitigation of the system primary frequency deviations during containment period. The Great Britain (GB) test system, for the Gone-Green planning scenario for the year 2030 (GG2030), is used to evaluate the effects of the proposed FAPI controllers on the dynamics of the system frequency within the frequency containment period. Thanks to proposed FAPI controllers, it is possible to reach up to 70% for the share of wind power generation without violating the threshold limits for frequency stability. For verification purposes, a full-scale wind turbine facilitated with each FAPI controller is tested in EMT real-time simulation environment.

Horizontal axis wind turbine testing at high Reynolds numbers

The flow conditions of a full-scale wind turbine are reproduced in a laboratory with dynamic similarity, using a pressurized wind tunnel. Aerodynamic scale-effects persist at higher Re than previously believed, and it is shown that the boundary layer state is critical for turbine performance.

Numerical study on the effect of blade surface deterioration by erosion on the performance of a large wind turbine

As the demand for the development of onshore wind farms in areas with low wind speeds and large offshore wind farms increases, the size of the wind turbine and its rotor has also increased rapidly. An increase in the rotor diameter implies an increase in the relative wind velocity (with respect to each cross section in the radial direction of the blade) near the tip region of the blade. This in return accelerates the surface damage caused by the erosion of the leading edge, thereby increasing the frequency of maintenance and lowering competitiveness in the cost of energy. In this study, computational fluid dynamics (CFD) analysis was performed to analyze the correlation between the leading-edge erosion damage and output performance of the blade. CFD simulations were performed using a tip airfoil (NACA 64_618) and a full-scale wind turbine (NREL 5 MW) based on the state of erosion of discarded blades considering approximately 12 years of maintenance-free operation. The irregular erosion at the airfoil leading edge results in premature stall phenomena and reduces the aerodynamic efficiency. Thus, the accurate analysis of the flow separation point and flow change is necessary. Therefore, three-dimensional transient CFD analysis was performed to consider the complex flow generated on the blade surface. The erosion at the leading edge reduced the airfoil lift by up to 23% and drag by 100%, reducing the aerodynamic efficiency, which in effect reduced annual energy production by up to 4%.

Characterization of Wind Turbine Wakes with Nacelle-Mounted Doppler LiDARs and Model Validation in the Presence of Wind Veer

Accurate prediction of wind turbine wakes is important for more efficient design and operation of wind parks. Volumetric wake measurements of nacelle-mounted Doppler lidars are used to characterize the wake of a full-scale wind turbine and to validate an analytical wake model that incorporates the effect of wind veer. Both, measurements and model prediction, show an elliptical and tilted spanwise cross-section of the wake in the presence of wind veer. The error between model and measurements is reduced compared to a model without the effect of wind veer. The characterization of the downwind velocity deficit development and wake growth is robust. The wake tilt angle can only be determined for elliptical wakes.

An efficient computational model for fluid-structure interaction in application to large overall motion of wind turbine with flexible blades

Abstract This paper proposes a very efficient computational model for fluid–structure interaction problems corresponding to steady-state flow representing a large overall motion of wind turbines with flexible blades. The model of turbine blades is based upon the 3D solids finite elements with drilling rotations. The proposed 3D solids model is fully able to describe the flexibility blades large overall motion and easily capture both bending and torsional motion thanks to using an enhanced strain field. The model efficiency is further reinforced by using the 3D panel method that fits naturally with proposed 3D solid finite elements for blades. The proposed panel method is the corresponding modification of the potential fluid flow by introducing a vorticity layer at the fluid–structure interface and Bernoulli’s conservation momentum equation in order to provide quantification for the blade thrust. The fluid–structure interaction is enforced through an efficient iterative procedure providing on one hand a very fast computation of aerodynamic loads, which is sufficiently accurate for computing the overall thrust on the blade, and on the other hand a sufficiently accurate representation of the stress states suitable for fatigue studies. The proposed computational model performance is illustrated with several numerical simulations, including the practical case of a full-scale NREL 5MW wind turbine.

Active Flow Control on Vertical Tail Models

Active flow control (AFC) subscale experiments were conducted at the Lucas Wind Tunnel of the California Institute of Technology. Tests were performed on a generic vertical tail model at low speeds. Fluidic oscillators were used at the trailing edge of the main element (vertical stabilizer) to redirect the flow over the rudder and delay or prevent flow separation. Side force increases in excess of 50% were achieved with a 2% momentum coefficient () input. The results indicated that a collective of about 1% could increase the side force by 30–50%. This result is achieved by reducing the spanwise flow on the swept back wings that contributes to early flow separation near their tips. These experiments provided the technical backdrop to test the full-scale Boeing 757 vertical tail model equipped with a fluidic oscillator system at the National Full-scale Aerodynamics Complex 40-by 80-foot Wind Tunnel, NASA Ames Research Center. The is shown to be an important parameter for scaling a fluidic oscillator AFC system from subscale to full-scale wind tunnel tests. The results of these tests provided the required rationale to use a fluidic oscillator AFC configuration for a follow-on flight test on the Boeing 757 ecoDemonstrator.

Hybrid RANS/LES Turbulence Model Applied to a Transitional Unsteady Boundary Layer on Wind Turbine Airfoil

A hybrid Reynolds-averaged Navier Stokes/large-eddy simulation (RANS/LES) turbulence model integrated with a transition formulation is developed and tested on a surrogate model problem through a joint experimental and computational fluid dynamic approach. The model problem consists of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter. The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near wake are well captured, owing to the turbulence-resolving large eddy simulation mode that was activated in the wake. The hybrid model switched between RANS and LES modes outside the boundary layers, as expected. According to the experimental and simulation results, the airfoil encountered local flow angle variations up to ±50°. Further analysis through a phase-averaging technique found phase lags in the airfoil boundary layer along the chordwise locations, and both the phase-averaged and mean velocity profiles collapsed into the Law-of-the-wall in the range of 0 < y + < 50 . The features of high blade-loading fluctuations due to unsteadiness and transitional boundary layers are of interest in the aerodynamic studies of full-scale wind turbine blades, making the current model problem a comprehensive benchmark case for future model development and validation.

Benchmarks for Model Validation based on LiDAR Wake Measurements

Technology development and design decisions in wind energy are often based on results from simulations performed for individual wind turbines or entire wind plants. It is therefore critical to ensure that the models being used for research and industry applications in wind energy be thoroughly validated against measurements. A full-system validation of wind plant simulations must consider the atmospheric inflow, the response of the wind turbines, and their wakes. This task is complicated by the lack of freely available, quality-controlled, high-quality measurements. Here, such measurements are used to offer a validation exercise that can be used to assess the accuracy of models of any fidelity level. When it comes to real-world measurements, the dataset considered herein is simple in terms of terrain but exhibits pronounced diurnal cycles. Instead of a full-scale wind plant, we consider an individual research-scale, utility wind turbine instrumented for power and loads measurements. Three benchmarks are defined, with increasing levels of complexity: near neutral, slightly unstable, and very stable atmospheric stratification. Through comparisons between observations and simulations, the benchmarks provide complementary information about the model performance and its ability to reproduce mean and dynamic wake characteristics. This article describes the measurements and methodology used to define these benchmarks and provides the information required to perform simulations and conduct the model-measurement comparison. The objective is to provide a robust wake model validation exercise open to anyone, which will serve to minimize uncertainty in model validation practices related to varying methodologies across simulation tools and users.

Field Validation of Generic Type 4 Wind Turbine Models Based on IEC and WECC Guidelines

The generic wind turbine models developed in recent years by the International Electrotechnical Commission (IEC) and the Western Electricity Coordinated Council (WECC) are intended to meet the needs of public, standard, and relatively simple (small number of parameters and computational requirements) wind turbine and wind farm models used to conduct transient stability analysis. Moreover, the full-scale converter wind turbine technology referred to as Type 4 by IEC and WECC, is increasingly used in current power systems due to its control benefits. Hence, the development of this generic model has become a priority. This study presents the validation of two generic Type 4 wind turbine models, which have been developed in accordance with the IEC and WECC guidelines, respectively. Field data collected from a real wind turbine located in a Spanish wind farm was used to validate both generic Type 4 wind turbine models following the IEC validation guidelines. Ten different test cases are considered, varying not only the depth and duration of the faults but also the load of the wind turbine. The parameters of the models were kept constant for all the simulation cases, aiming to evaluate the accuracy of the models when facing different voltage dips.

Multirotor UAV-Based Platform for the Measurement of Atmospheric Turbulence: Validation and Signature Detection of Tip Vortices of Wind Turbine Blades

AbstractThe present study describes the development of a technique for the measurement of atmospheric turbulence and temperature at a point in space based on the integration of a fast-response multihole pressure probe and a thermocouple with an inertial measurement unit on a multirotor UAV-based platform. This allows for an accurate measurement of time series of the three components of the velocity vector and temperature at any point in space in which the UAV can fly within the limitations of its autonomy. The presented technique relies on an accurate correction of the three-component velocity vector measured by the pressure probe on the frame of reference of the UAV—noninertial—with the information provided by the inertial measurement unit. The study includes a validation of the technique against sonic anemometry and the measurement of the signature of tip vortices shed by the blades of a full-scale wind turbine as an example of its potential.

A Large-Eddy Simulation-Based Assessment of the Risk of Wind Turbine Failures Due to Terrain-Induced Turbulence over a Wind Farm in Complex Terrain

The first part of the present study investigated the relationship among the number of yaw gear and motor failures and turbulence intensity (TI) at all the wind turbines under investigation with the use of in situ data. The investigation revealed that wind turbine #7 (T7), which experienced a large number of failures, was affected by terrain-induced turbulence with TI that exceeded the TI presumed for the wind turbine design class to which T7 belongs. Subsequently, a computational fluid dynamics (CFD) simulation was performed to examine if the abovementioned observed wind flow characteristics could be successfully simulated. The CFD software package that was used in the present study was RIAM-COMPACT, which was developed by the first author of the present paper. RIAM-COMPACT is a nonlinear, unsteady wind prediction model that uses large-eddy simulation (LES) for the turbulence model. RIAM-COMPACT is capable of simulating flow collision, separation, and reattachment and also various unsteady turbulence–eddy phenomena that are caused by flow collision, separation, and reattachment. A close examination of computer animations of the streamwise (x) wind velocity revealed the following findings: As we predicted, wind flow that was separated from a micro-topographical feature (micro-scale terrain undulations) upstream of T7 generated large vortices. These vortices were shed downstream in a nearly periodic manner, which in turn generated terrain-induced turbulence, affecting T7 directly. Finally, the temporal change of the streamwise (x) wind velocity (a non-dimensional quantity) at the hub-height of T7 in the period from 600 to 800 in non-dimensional time was re-scaled in such a way that the average value of the streamwise (x) wind velocity for this period was 8.0 m/s, and the results of the analysis of the re-scaled data were discussed. With the re-scaled full-scale streamwise wind velocity (m/s) data (total number of data points: approximately 50,000; time interval: 0.3 s), the time-averaged streamwise (x) wind velocity and TI were evaluated using a common statistical processing procedure adopted for in situ data. Specifically, 10-min moving averaging (number of sample data points: 1932) was performed on the re-scaled data. Comparisons of the evaluated TI values to the TI values from the normal turbulence model in IEC61400-1 Ed.3 (2005) revealed the following: Although the evaluated TI values were not as large as those observed in situ, some of the evaluated TI values exceeded the values for turbulence class A, suggesting that the influence of terrain-induced turbulence on the wind turbine was well simulated.

Understanding Structure Ignition Vulnerabilities Using Mock-up Sections of Attached Wood Fencing Assemblies.

Firebrand production from structure combustion becomes a key factor in the magnitude of how quickly a large outdoor fire may spread. Post-fire disaster investigations suggest that attached building components, such as wood fencing assemblies are known to be prone to ignition in these fires, and may provide pathways to structure ignition. Here, a comparison of ignition results from full-scale fencing assembly experiments conducted using a full-scale wind tunnel facility, to mock-ups of full-scale fencing assemblies using the recently developed experimental capability at the National Research Institute of Fire and Disaster (NRIFD) are discussed. In both experimental facilities, the fencing assemblies were exposed to firebrand showers using custom built continuous-feed firebrand generators with size and mass distributions similar to those generated from structure combustion. Similar ignition behaviors were observed between the full-scale fencing assemblies and the mock-up of full-scale fencing assemblies. Additional experiments are required for other fencing assembly types to further verify these important findings.

Flexural Test on a Full-Scale 60-kW Wind Turbine–Tower Telescopic Steel Pipe

Flexural Test on a Full-Scale 60-kW Wind Turbine–Tower Telescopic Steel Pipe

Analysis of near wake recovery scale model vawt hybrid wind turbin in wind tunnel

CFD simulations of full scale wind turbine have been carried out to predict recovery of wake that occur behind the hybrid VAWT turbine double, which states that recovery starts to occur in plane x/d = 4, verification of this result needs to be done. This study tested and measured the wind speed behind the scale model turbine in the wind tunnel. The purpose of this study was to create a prototype scale model of the VAWT hybrid, test it in the wind tunnel. Statistical methods will be used in this study to process data and determine the recovery position of wake from the VAWT double hybrid. The results show that wake recovery in wind tunnel experiment, in field x/d = 3 with 99%, compare with wake recovery occurs in simulation, shown a show the same trend, but need further investigation with similarity and Reynold number.

Elastic shape morphing of ultralight structures by programmable assembly

Ultralight materials present an opportunity to dramatically increase the efficiency of load-bearing aerostructures. To date, however, these ultralight materials have generally been confined to the laboratory bench-top, due to dimensional constraints of the manufacturing processes. We show a programmable material system applied as a large-scale, ultralight, and conformable aeroelastic structure. The use of a modular, lattice-based, ultralight material results in stiffness typical of an elastomer (2.6 MPa) at a mass density typical of an aerogel . This, combined with a building block based manufacturing and configuration strategy, enables the rapid realization of new adaptive structures and mechanisms. The heterogeneous design with programmable anisotropy allows for enhanced elastic and global shape deformation in response to external loading, making it useful for tuned fluid-structure interaction. We demonstrate an example application experiment using two building block types for the primary structure of a 4.27 m wingspan aircraft, where we spatially program elastic shape morphing to increase aerodynamic efficiency and improve roll control authority, demonstrated with full-scale wind tunnel testing.

Fusion joining of thermoplastic composite wind turbine blades: Lap-shear bond characterization

Wind turbine blades are typically manufactured from a small number of components which are bonded together with an adhesive. Over the life span of a wind turbine, the static and fatigue loads in varying environmental conditions can lead to cracking and/or debonding of the adhesive joints, ultimately leading to blade structural collapse. The objective of this work is to investigate fusion joining of wind turbine blades manufactured using thermoplastic resin. Thermoplastic resins for wind turbine blades can reduce cycle times and energy consumption during manufacturing and facilitate end-of-life recycling and on-site manufacturing. Additionally, fusion joining of these materials can replace adhesives, resulting in stronger and more robust blades. This work showed that, compared to typical adhesives used in wind turbine blades, fusion welding resulted in an increase in both the static and fatigue lap-shear strength as compared to bonded thermoplastic composite coupons. This initial coupon-scale research suggests that there is potential for developing fusion welding techniques for full-scale wind turbine blades.