Recent  

Aerodynamic and acoustic field measurements on operating large-scale wind turbines are key for the further reduction of the costs of wind energy. In this work, a novel cost-effective MEMS-based aerodynamic and acoustic wireless measurement system that is thin, non-intrusive, easy to install, low power, and self-sustaining is designed and tested.

In this work, we conduct a validation study to compare a numerical solver against measurements obtained from the offshore Lillgrund windfarm. By reusing a previously developed inflow dataset, the atmospheric conditions at the wind farm were successfully recreated, and the general performance trends of the turbines were captured well. The work increases the reliability of numerical wind farm solvers, while highlighting the challenges of accurately representing large wind farms using such solvers

This paper is focused on the impact of modeling different effects, such as forest canopy, buoyancy, and Coriolis forces, on the wind resource over a complex terrain site located near Perdigão, Portugal. A numerical model is set up and results are compared with field measurements. The results show that including a forest canopy improves the predictions close to the ground at some locations on the site, while the model with buoyancy effects performed better at other locations.

In this work, a range of simulations are carried out with seven different wind modelling tools at five different complex terrain sites and the results compared to wind speed measurements at validation locations. This is then extended to AEP estimations (without wake effects), showing that wind profile prediction accuracy does not translate directly or linearly to AEP accuracy. It is therefore vital to consider overall AEP when evaluating simulation accuracies.

Wake steering is an emerging wind power plant control strategy where upstream turbines are intentionally yawed out of alignment with the incoming wind, thereby “steering” wakes away from downstream turbines. Trade-offs between the gains in power production and fatigue loads induced by this control strategy are the subject of continuing investigation. In this study, we present an optimization approach for efficiently exploring the trade-offs between power and loading during wake steering.

Lidar measurements combined with meteorological sensors reveal the strong directional and stability dependence of the wake strength in the direct vicinity of wind farm clusters.

We consider characteristics and drivers of loads experienced by wind turbine main-bearings using simplified models of hub and main-bearing configurations. Influences of deterministic wind characteristics are investigated for 5, 7.5 and 10 MW turbine models. Load response to gusts and wind direction changes are also considered. Cubic load scaling is observed, veer is identified as an important driver of load fluctuations and strong links between control and main-bearing load response are shown.

We proof the dynamic inflow effect due to gusts in wind tunnel experiments with MoWiTO 1.8 in the large wind tunnel of ForWind – University of Oldenburg, where we created coherent gusts with an active grid. The effect is isolated in loads and rotor flow by comparison of a quasi-steady and a dynamic case. The observed effect is not caught by common dynamic inflow engineering models. An improvement to the Øye dynamic inflow model is proposed matching experiment and corresponding FVWM simulations.

In this work, free-vortex wake (OLAF) and low-fidelity blade-element momentum (BEM) structural results are compared to high-fidelity simulation results for a highly-flexibly downwind turbine for varying inflow conditions. Overall, OLAF results were more consistent than BEM results when compared to SOWFA results under challenging inflow conditions. Differences between OLAF and BEM results were dominated by yaw misalignment angle, with varying shear exponent and TI causing more subtle differences.

A consistent method of using two-dimensional airfoil data when using generalized lifting-line methods for the aerodynamic load calculation of non-planar horizontal-axis wind turbines is described. The important conclusions from the unsteady two-dimensional airfoil aerodynamics are highlighted. The impact of using a simplified approach instead of using the full model on the prediction of the aerodynamic performance of non-planar rotors is shown numerically for different aerodynamic models.

Wind turbines aeroelasticity is becoming more and more important because turbine sizes are increasing leading to more slender blades. On the other side, complex terrains are of interest, because far away from urban areas. These regions are characterized by low velocities and high turbulence and are mostly influenced by the presence of the forest and that is why it is necessary to develop high fidelity tools to correctly simulate the wind turbine's response.

Joint probability distribution of 10-minute mean wind speed and the standard deviation is proposed using Gaussian mixtures, and shown to agree well with 15-years of measurements. The results from the model could be taken as inputs for structural reliability analysis and uncertainty quantification of wind turbine design loads, especially towards the effects of extreme wind turbulence.

In this paper we present a revised dynamic control-oriented wind farm model. The model can simulate turbine wake behaviour in heterogeneous and changing wind conditions at a very low computational cost. It utilizes a three-dimensional turbine wake model which also allows to capture vertical wind speed differences. The model could be used to maximise the power generation of with farms, even during events like a wind direction change. It is publicly available and open for further developed.

Non-normal wind profiles with negative shear in part of the profile (such as e.g. low-level jets) are frequently occurring in coastal environments and are important to take into consideration for offshore wind power. Using observations from a coastal site in the Baltic Sea, we analyse in which meteorological and sea state conditions these profiles occur and study how they alter the turbulence structure of the boundary layer compared to normal profiles.

The ARCWIND project contribute to reduce the technical uncertainties of floating wind technology. The SATH floating platform from Saitec was up-scaled to support the wind turbine 10MW INNWIND. An innovative testing approach named Software-in-the-Loop (SiL) was successfully applied to integrate the wind turbine loads in the SATH scaled experiments. The OpenFAST numeric tool was calibrated and produced results in agreement with experiments about the SATH response under wind and wave loading.

In this research, a cyclic p-y overlay model for monopiles in sand soils could be developed by comparison of numerical simulations of monopile behaviour once under monotonic and once under cyclic loading with a defined number of load cycles (utilizing the stiffness degradation method). The new cyclic overlay model gives plausible results and can be applied to any monotonic p-y approach for monopiles in sand.

Though large wind turbines are appealing to reduce costs, larger blades are prone to aero-elastic instabilities due to their long, slender, highly flexible nature. And, new rotor concepts are emerging including two-bladed rotors and downwind configurations. We introduce a comprehensive evaluation of flutter behavior including classical flutter and edgewise vibration for large-scale two-bladed rotors. The study aims to provide designers with insights to mitigate flutter in future designs.

The sensitivity of WRF mesoscale modelling framework in accurately representing and predicting wind farm level environmental variables for the extreme case of Storm Ciara over the Belgian North Sea is investigated in this study. The overall results indicate highly sensitivity simulation results, with supporting conclusions for scale-aware physics parameterizations to better reproduce wind-related variables and ensemble averaging as a promising approach for precipitation.

As wind farm developments expand offshore, it is becoming more important for us to accurately forecast winds above coastal waters so we can capitalize on the offshore wind energy resource as best as possible. Weather models rely on various inputs to generate their forecasts, and one of them is sea surface temperature (SST). In this study, we evaluate how the SST product used in a model (there are numerous options) can influence the forecast and find that it can make a significant difference.

The current turbulent wind field models stated in the IEC 61400-1 standard underestimate the probability of extreme changes in wind velocity. This underestimation can lead to the false calculation of extreme and fatigue loads on the turbine. In this work, we are trying to apply a random time-mapping technique to one of the standard turbulence models to adapt to such extreme changes. The turbulent fields generated are compared with a standard wind field to show the effects of this new mapping.

The spoiler is found to efficiently rearrange the mean flow seen by thick aerofoil: adding lift throughout the positive angles of attack, the drawback is a high drag penalty coupled with high unsteadiness of the aerodynamic forces. The impact of this type of excitation will be quantified further in term of energy production and fatigue in future work.

Measuring the variability of the wind is essential to operate the wind turbines safely. Lidars of different configurations have been placed on the turbines’ nacelle to measure the inflow remotely. This work found that the multiple-beam lidar is the only one out of the three employed nacelle lidars that can give detailed information about the inflow variability. The other two commercial lidars, which have 2 and 4 beams, respectively, measure only the fluctuation in the along-wind direction.

This work evaluates which wind-inflow- and wake-related parameters have the greatest influence on fatigue and ultimate loads for turbines in a small wind farm. Twenty-eight parameters were screened using an elementary effects approach to identify the parameters that lead to the largest variation in these loads of each turbine. The findings show the increased importance of non-streamwise wind components and wake parameters in fatigue and ultimate load sensitivity of downstream turbines.

The seismic soil-structure interaction of wind turbine support structures is investigated. Wind turbine support structures are modeled by the sway-rocking model and its seismic loadings are analytically derived by complex response spectrum method. To improve the prediction accuracy of the shcar force on footings, an upper limit of modal damping ratios is proposed. The proposed method is demonstrated to be capable to accurately and efficiently estimate the seismic loadings on towers and footings.

In this work, an adaptive control strategy for controlling the lifetime of wind turbine components is proposed. Performance of the lifetime controller is adapted based on real-time health status of the rotor blades to guaranty a predefined lifetime. It shows promising results in lifetime control of blades without speed regulation and tower load mitigation trade-off. It can be applied in optimizing maintenance scheduling of wind farms, which increases reliability and reduces maintenance costs.

This paper investigates the opportunities and limits of two additional devices that improve the aerodynamic performance of wind turbine rotor blades. The objective of attaching these relatively small add-ons is the optimization of the annual energy production over a time period of at least 20 years by mitigating the effects of typical wear-out effects, such as the surface erosion of rotor blades. Hence, the study is a contribution to the reliable and long-term generation of renewable energy.

A brief summary of current regulations and recommendations for the serviceability limit state dimensioning of offshore monopile foundations in sand supporting wind turbines is given. Results from small scale model experiments are presented, discussed and compared to the findings of other research groups to contribute to a better understanding of the complex processes associated with the cyclic load-bearing behavior of piles and to the development of improved calculation approaches.

In this work, we study parks of large-scale airborne wind energy systems using a virtual flight simulator. The virtual flight simulator combines numerical techniques from flow simulation and kite control. Using advanced control algorithms, the systems can operate efficiently in the park despite turbulent flow conditions. For the three configurations considered in the study, we observe significant wake effects reducing the power yield of the parks.

Like young children without help, wind turbines are bad at sharing. Those that are first in line (most upstream) take all the fresh air leaving little for those downstream. This research shows how turbines can operate to share the wind resource better and what parameters are most important for optimizing this technique. Results indicate that power gains of 10 % can be achieved if upstream turbines are operated differently, which may help operators produce more wind power.

Distinct zonations with its own fauna and flora were observed. Algae and blue mussels dominated the structures from the surface down to 20 m, with tube building fan worms and plumose anemones as the main colonisers found below. The park is in its “intermediate” stage and moving towards the “apex” stage, with anemones covering most of the structures. The study was conducted to investigate if a floating wind park has the same fauna and zonations observed on traditional non-floating wind parks.

The article delineates a novel procedure to use 10-minute measurement statistics with few known parameters of the wind turbine to determine the long-term fatigue damage probability and compares this with theoretically expected levels to provide an indicator of structural reliability and remaining life. The results are validated with load measurements from a wind turbine inside an offshore wind farm.

Numerical weather prediction models are used to predict how wind turbines will interact with the atmosphere. Here, we characterize the uncertainty associated with the choice of turbulence parameterization on modeled wakes. We find that simulated wind speed deficits in turbine wakes can be significantly sensitive to the choice of turbulence parameterization. As such, predictions of future generated power are also sensitive to turbulence parameterization choice.

The small wind community relies on simplified wind models and energy production simulation tools to obtain energy generation expectations. We gathered actual wind speed and turbine production data across the U.S. to test the accuracy of models and tools for small wind turbines. This study provides small wind installers and owners with the error metrics and sources of error associated with using models and tools to make performance estimates, empowering them to adjust expectations accordingly.

This work presents a shape optimization framework based on computational fluid dynamics. The design framework is used to optimize wind turbine blade tips for maximum power increase while avoiding that extra loading is incurred. The final results are shown to align well with a related literature. The resulting tip shape, could be mounted on already installed wind turbines as a sleeve-like solution, or be conceived as part of a modular blade with tips designed for site-specific conditions.

Based on the IEC standards, a limited number of simulations is sufficient to calculate the extreme and fatigue loads on a wind turbine. However, this means inaccuracy in the output statistics. This paper aims to build a surrogate model on BEM aerodynamic model simulations output employing non-intrusive Polynomial Chaos Expansion. The surrogate model is then used in a large number of Monte Carlo simulations to provide an accurate statistical estimate of the loads.

This work introduces the FLOW Estimation and Rose Superposition (FLOWERS) wind turbine wake model. This model analytically integrates the wake over wind directions to provide a time-averaged flow field. This new formulation is used to perform layout optimization. The FLOWERS model provides a smooth flow field over an entire wind plant at fraction of the computational cost of the standard numerical integration approach.