ReliaBlade2 research project

Project title: ReliaBlade2 – Development of new design methods for rotor blades

Summary:

The reliability of rotor blades is particularly important for the safe and economical operation of wind turbines. However, despite the wind energy industry’s many years of experience in the design and operation of rotor blades, cracks still occur in the rotor blade structure, which are the cause of costly repairs and operational failures. This indicates a lack of knowledge in the development of damage due to fatigue. Important physical relationships have not yet been fully understood, which includes in particular material modeling and comprehensive validation of extended models. Digital twins can also help to operate rotor blades even more safely and cost-effectively in the future. However, not all methods are yet available to map probabilistic uncertainties in a digital twin. A consortium of research institutions and industrial partners has come together to close the aforementioned knowledge gaps.

The sub-project of ForWind Hannover pursues the all-encompassing goal of increasing the structural reliability and economic efficiency of rotor blades. To this end, a new design philosophy for the fatigue of rotor blades is to be established in the industry, which includes progressive matrix damage. This will be based on fatigue damage models developed in-house and partly used in the industry. Characterization and validation tests at coupon level are an integral part of the sub-project. In addition, methods for the creation of probabilistic digital twins are to be developed that incorporate spatially and statistically distributed manufacturing imperfections with the help of AI-based model updating. The models and methods developed are to be applied for the first time to an industrially manufactured rotor blade and validated by whole-blade tests.

ElMaR research project

Project title: ElMaR – Non-destructive determination of local material parameters in rotor blade components

Summary:

In the design of rotor blades, fiber composite materials are regarded as ideally smeared, homogeneous materials. The required material parameters are determined in material tests at coupon level. It is known that the material properties of fiber composites are subject to fluctuations. The uncertainties of the material parameters are taken into account in the blade design by means of partial safety factors. Spatial variation of the material parameters and their possible consequences are not taken into account. However, a closer look reveals that the assumption of a homogeneous material is already incorrect at coupon level. It is to be expected that the spatial variation of material parameters at the structural level of a rotor blade will be significantly higher due to the manual work steps. This also increases inaccuracies in the prediction of fatigue life and load-bearing capacity, which leads to an unnecessary reduction in structural reliability. In order to develop probabilistic models, specify partial safety factors and thus increase the structural reliability of rotor blades, the project pursues the following specific objectives: – A method for the non-destructive determination of spatially fluctuating material parameters in rotor blade components is to be developed. The research hypothesis is that a combination of established imaging methods, modern machine learning algorithms and high-resolution simulation methods is suitable for combining very high accuracy with short computing times. – The method is to be validated in the laboratory at the structural level. – After completion of the project, a consortium with industrial participation is to be organized in order to connect a funded joint research project with the aim of further developing the method towards industrial applicability.

EuroWindWakes research project

Project title: EuroWindWakes: Multiscale Modeling of European Wind Energy Wake Effects

Summary:

• The planned dense development of offshore wind farms in the North Sea will make wake effects and the global blockage effect more important for calculating electricity yields. Current models only depict this with great uncertainty.
• The international research project EuroWindWakes aims to significantly reduce these uncertainties by improving and validating the methods, thus enabling optimized maritime spatial planning and reliable power generation forecasts. This includes the wake effects for the entire North Sea.

Contents and methodology:

Wakes and the global blockage effect can significantly reduce electricity yields due to increased turbulence and reduced wind speeds.

The models currently used to calculate electricity yields can only depict these effects with great uncertainty. These uncertainties can have a significant impact on both the economic benefit due to an overall reduction in electricity generation and the economic profitability due to overly optimistic bids in the tenders for offshore areas.

The aim is to reduce the prediction uncertainty from 20 to 30 percent to less than 10 percent. To achieve this goal, the cooperation partners from Germany, Denmark and the Netherlands will improve and validate modeling approaches for wake effects on a European scale. Recommendations for action derived from the results are made available to all relevant stakeholders via the industry partners involved in the project.

In addition, EuroWindWakes will help to create an important hub for the emerging European Center of Excellence for Wind Energy, an initiative of the European Energy Research Alliance (EERA JP Wind).

Doctoral candidate network AptWind

Project title: AptWind – Atmospheric Physics and Turbulence for Wind Energy Doctoral Network

Summary:

The aim is to train a new academic generation that has a deep understanding of the interplay between atmospheric flow physics and turbulence, while at the same time being able to develop innovative industrial applications and products from the scientific findings. To this end, doctoral students are specifically supported with scholarships. AptWind pursues specific scientific questions: Four key research questions address, among other things, the effects of relevant flow events on rotors of wind turbines with an output of more than 15 MW or the improvement of numerical simulations.

AptWind ensures that a new generation of scientific specialists are not only well trained in the field of atmospheric flow physics, which is important for understanding wind energy, but also ensures that scientists are well networked with each other and with industry. As a result, scientific findings will quickly find application in industry.

FLORIDA research project

Project title: FLORIDA – Floating wind turbine wake interaction and Dynamics

Summary:

With the shift towards floating offshore wind farms, new problems arise when investigating the turbulent wakes of wind turbines The additional floating motion of the platforms affects the interaction of the turbine with the incoming wind field and thereby the generation of the wakes, which are already complex in their evolution and structures for bottom-fixed machines. Different platform types show design-specific damping of their motion, which is induced by ambient ocean waves and the interaction of the turbine with the turbulent incoming wind field. This results in periodic motion patterns, which are also be printed on the dynamics of the wakes (wake center) and even trigger a faster recovery of the wake velocity deficit. Either way, in wind farm configurations these wakes will hit other floating turbines and will have an impact on their performance and on their floating behavior.

For farm layout optimization and to decrease fatigue loads and thus maintenance times (that are costly and time-consuming offshore), it is therefore important to understand the wake dynamics of floating wind turbines. In the systematic investigation of wind turbine wake dynamics, the relevance of wind tunnel experiments is widely acknowledged. In the project FLORIDA, we therefore propose to extend the investigations to floating wind turbines by adding pre-defined motion to turbine models, under realistic as well as user-defined turbulent inflow conditions. The goal is to identify the impact of floating motion in various degrees of freedom on the wake dynamics with focus on wake meandering. In addition, special turbulent inflow conditions are used to selectively investigate the influence of different length scales on wake meandering. Based on the experimental data, new wake models will be developed for floating wind turbines that capture the floating-added dynamics of the wake meandering.

The approach includes both the further development of existing dynamic models and the extension with stochastic methods. The models will be used to generate wind fields with realistic wake characteristics of floating turbines as input for fully-coupled simulations and wave tank Software-in-the-Loop experiments in which (1) a software calculates the aerodynamic loads acting on the floating turbine with such waked wind fields and (2) the aerodynamic loads are emulated with 6 degree of freedom actuators. The influence of the incoming waked wind fields on the floater behavior will be then investigated.

optDIC research project

Project title: optDIC – Optimizationof the DIC measurement system for detecting deformations on wind turbines

Summary:

The design of modern wind turbines is strongly influenced and limited by aeroelastic and structural dynamic aspects. To validate these design methods, extensive long-term deformation measurements on wind turbines are required, which are currently not available. In the “optDIC” project, the optical measurement technology Digital Image Correlation (DIC) is being further developed in order to enable long-term deformation measurements on wind turbines and thus reduce the lack of experimental validation data. By using suitable artificial intelligence methods or conventional image processing algorithms, the rotor blades are to be detected in real time, thereby significantly reducing the amount of data recorded. In addition, the measurement method currently used is to be extended so that changes in wind direction can be compensated for. An automated evaluation of the recorded measurement data should also increase the industrial and scientific attractiveness of DIC. As part of this project, the current DIC measurement system is to be made weatherproof with regard to long-term measurements. Finally, long-term field measurements of transient deformations on a wind turbine will be used to test and evaluate the data processing and analysis methods developed.

WindRamp II research project

Project title: WindRamp II – Observer-based shortest-term power forecast of large offshore wind farm clusters for system integration and grid stabilization

Summary:

With the “WindRamp II” project, ForWind (AG WESys at the Carl von Ossietzky University of Oldenburg) is building on the successful work of the WindRamp project completed in December 2023, in which an observer-based shortest-term forecast for wind speed and power was researched. In WindRamp II, the ForWind subproject aims to extend the observer-based forecast to heterogeneous wind farm clusters with very large turbines, to develop new methods for increased forecast accuracy and an extended forecast horizon. The improved power forecasts are intended to achieve more reliable system integration of wind energy with less need for balancing energy and warnings in the event of expected ramp events. The novel technology of long-range scanning lidar devices developed in the WindRamp project will contribute to expanding the forecasting horizon and improving quality in WindRamp II.

The BMWK-funded project is coordinated by ForWind and carried out together with the partners energy & meteo Systems, DLRVE and RWE as well as METEK and Abacus Laser as associated partners.

WindDyS research project

Project title: WindDyS – Development and investigation of a novel dynamic stall model for the preliminary design of wind turbine rotor blades

Objective and reason for the project:

The WindDyS project investigated the dynamic behavior of aerodynamic cross-section profiles of rotor blades for wind turbines. If the angle of attack over which the airfoils are approached is changed dynamically, this can lead to a change in behavior in the area of the stall – the so-called dynamic stall. The WindDyS project has been concerned with simulating this behavior precisely with numerical flow calculations and developing a reliable model with which these calculations can be transferred to industrial load calculations. Until now, adapted models originally developed for helicopter aerodynamics have been used for this purpose. The aim of the project is to use an improved wind energy-specific model to promote the development of longer, lighter and thus also more flexible rotor blades in order to enable the construction of fewer but larger wind turbines in the future and thus conserve the resources required for the energy transition.

Methods and work steps

In the project, extensive numerical flow simulations were carried out for various profile geometries, especially thick ones, which depict their properties under different conditions. The results of the high-resolution flow simulations should be used to create an improved model for the occurrence of dynamic stall on wind energy profiles. Based on the Onera model, an approach was implemented which, with corrections to the Onera model, allows the results of such calculations to be mapped in a simplified and fast model. This provides a necessary second-order approach for mapping the dynamic properties of the dynamic stall. Implementing the second-order model in the open source software OpenFAST requires significant adjustments to the core code, which can be implemented together with the code developer in the future.

MeTuSA research project

Project title: MeTuSA – Methods for the simulation of vortex-excited tower vibrations and for the site-specific design of tall wind turbine towers

Summary:

The increasing size of wind turbines also increases the flexibility of components and the risk of aeroelastic instabilities. In particular, vortex-induced vibrations (ViV) of the tower in the structure of the system should be mentioned here. With this instability, a resonance between the tower’s natural frequency and the cyclically separating, transient vortex paths in the tower wake leads to a critical upswing. This can lead to structural damage to the wind turbine as well as to stress for the installation and maintenance personnel. Since there are no suitable calculation methods for site-specific simulation of this effect in the literature or in science, a new semi-empirical method is being developed in the MeTuSA project that enables the integration of tower vibrations in transient load simulations. In addition, the influences of site-specific meteorological conditions and countermeasures are being investigated in the project.

In addition to the development of the semi-empirical model, the sub-project of the University of Oldenburg contributes to this project primarily with wind tunnel experiments to form the database for modeling and to validate the simulations. For this purpose, the available wind tunnel and an active grid for the individual design of the user-defined inflow are used to investigate simplified tower models in various flow situations such as turbulence intensities and shear.

NearWake research project

Project title: NearWake – Modeling for the near wake

Summary:

Content and Methodology:

The sub-project of the University of Oldenburg is dedicated to researching a simplified stochastic model for the near wake. Wind field measurements are processed and classified for this purpose and used together with numerical data from large-eddy simulations for model development and validation.