IEA Wind Task 47

Innovative Aerodynamic Experiments and Simulations on Wind Turbines in Turbulent Inflow
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About Task 47

The aim of IEA Task 47 is to cooperate on the field of detailed aerodynamic measurements on MW scale wind turbines. Such measurements are extremely difficult to do and the only public example until now is the Danish DanAero experiment which was used in IEA Task 29. Recently several other countries initiated new experiments for turbines up to a scale of 8MW and they now all have to go through a similar learning process on these new measurement techniques. Sharing experiences is then a very fruitful way to steepen the learning curves.

The Task also includes analysis of aerodynamic measurements where moreover simulations are carried out on the 15 MW Reference Wind Turbine from IEA Task 37. These simulations give insight into the relevant aerodynamic problems for large scale wind turbines which is important information for the definition of the experimental programs.

The Operating Agent of the Task is TNO in the Netherlands, with support from DTU in Denmark

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Participation

Task 47 Participants

Task 47 is still in the start-up phase so the participating countries are not established yet. In the pre-decessor project IEA Task 29 a total of 29 research institutes and industries from 9 different countries (China, Denmark, France, Germany, Italy, Netherlands, Sweden, USA, Switzerland) participated which all expressed their support for a continuation through IEA Task 47. Also Finland will participate to Task 47

Who can participate in Task 47?

To participate in the research activities of Task 47, researchers must reside in a country that participates in the IEA Wind Agreement AND has agreed by official letter to participate in Task 47. The participating member country of the IEA Wind TCP must designate a lead institution that agrees to the obligations of Task participation (pay the annual fee and agree to perform specified parts of the work plan).

Active researchers (performing part of the work plan) benefit from meetings and professional exchange during the term of the Task. In the particular case of IEA Task 47 the measurement results will, where possible, be shared into the consortium so that  partners get first hand information from unique new data. Countries participating in the Task benefit from the information developed by the Task. The value of the research performed is many times the cost of the country participation fee or the labor contributed to carrying out the work plan.

For more information, contact the Operating Agents, Gerard Schepers and Koen Boorsma or the IEA Wind Secretariat.

Participation

Operating Agents

Please contact the Operating Agents below with any questions

Gerard Schepers

Task 47 Operating Agent

    Koen Boorsma

    Task 47 Operating Agent

      Helge Aagaard Madsen

      Task 47 Operating Agent

        Georg Pirrung

        Task 47 Operating Agent
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          Task 47 Publications

          Find more information about our publications and results in the publication tab or the link below

          Learn more about our published work here.

          Results

          Task 47 Roadmap

          The Task 47 begin date is January 1st 2021 after which it will run for 4 years until December 31st 2024. A detailed planning of the activities can be found under the tab Work Plan and Objectives but roughly speaking the following main activities can be distinguished:

          • Cooperation on new aerodynamic experiments
          • Turbulent calculations on the DanAero experiment. A comparison will be made on basis of statistical properties but also on a time series basis where special emphasis will be put on a consistent comparison between calculations and measurements. The calculations will be done in 2 rounds, the first round will start in 2021
          • Calculations on 15 MW RWT, where a  mutual comparison of low fidelity results with high fidelity results will be made. This will start with a check on the model description. This check will be finished in 2021 after which the actual calculations are carried out in 2 rounds.
          • Eventually the results of the project will be evaluated and it will lead to recommendations on model improvement and best practices on detailed aerodynamic experiments

          Meanwhile the kick-off meeting was held on-line in three sessions of 2.5 hours on April 6, 8 and 9 2021. At this meeting the planning of activities was refined and detailed for year 2021. The main activities which will be carried out in 2021 are listed in the time line which is given below

          The schedule of personal meeting is put on hold due to the Corona pandemic. If the situation improves personal meetings will be organised again. It is anticipated that they will be held on an annual basis, mostly in Europe in view of the fact that the majority of the participants is European but meetings in the US and China are anticipated too.

          More information can be found here.

          2021

          In 2021 the following main activities will be carried out:

          The cooperation between parties which perform detailed aerodynamic measurements will start up. Thereto several meetings with these parties will be organised

          The first calculational round on the DanAero turbine at turbulent conditions will be defined before August 1st 2021.

          The IEA 15 MW Reference wind turbine will be modelled by the various codes in the project. Thereto preparatory calculations (e.g. thrust curves, power curve and aero-elastic properties) will be finished on December 31st 2021. The comparison between model results is expected to form a check on a correct model input.

          2022-2024

          The planning for the period 2021-2024 still need to be refined. Roughly speaking the following actitvies are carried out.
          The cooperation between parties which perform detailed aerodynamic experiments will be strenghtened. Where possible experimental data are shared within the project group. Best practices for doing detailed aerodynamic experiments are formulated.

          Two rounds of calculations will be carried out on the DanAero experiment and the IEA 15 Reference wind turbine. Calculational results from models with a large variety in level of fidelity and calculational time are compared mutually where for the DanAero case a comparison between calculations and measurements is made also on a time varying basis. The results will be evaluated and recommendation for modelling large wind turbines are formulated.

          Task 47 FAQ //

          Frequently Asked Questions

          Get answers to our most commonly asked questions about IEA Wind TCP Task 47

          Why do we need detailed aerodynamic measurements?

          Specific aerodynamic measurements are needed to understand the very large challenges of the aerodynamics of large wind turbines in atmospheric flow. These measurements only can capture the details of the flow physics.
          Detailed aerodynamic measurements are even an absolute necessity when validating wind turbine design codes since a comparison with conventional measurements of global (rotor) blade loads is far too crude and it does not provide the accuracy of such codes. This is due to the fact that a good agreement between calculated and measured rotor (blade) loads is often caused by compensating errors (e.g. an overprediction at the root can be compensated by an  underprediction at the tip or an overprediction in lift can be compensated by an overprediction in drag). In such cases a comparison with global load measurement yields a good agreement and the very misleading conclusion that the code is accurate. An example is given in the figure  from IEA Wind Task 18.

           

          Ratio between ECN calculated and NREL Phase IV measured rotorshaft torque as function of wind speed

          Ratio between ECN calculated and NREL Phase IV measured rotorshaft torque as function of wind speed

          It shows the ratios between the rotor shaft torque calculated by TNO (ECN at that time) in comparison to measurements from the NREL Phase IV experiment as function of mean wind speed. A ratio of 1 implies a perfect agreement (i.e. the target value). A ratio > 1 implies an overprediction and a ratio < 1 implies an underprediction. The comparison is generally very good with the largest discrepancy being 10% at  roughly 13 m/s and discrepancies at other wind speed which are often 5% or even less. Hence in the conventional case where rotor shaft torque (or power) measurements would be available only, the conclusion is that the code is performing well. However the measurement of pressure distribution at 5 radial positions as available in the NREL experiment offers a much more detailed validation see the following figures,

          Ratio between ECN calculated and NREL Phase IV measured normal force as function of wind speed at 5 radial positions

          Ratio between ECN calculated and NREL Phase IV measured tangential force as function of wind speed at 5 radial positions

          These figures show the comparison of sectional forces in normal and tangential direction. It is then very striking to see very large discrepancies (tens of percents) between calculations and measurements in particular at the higher velocities. This shows that the good agreement between calculated and measured rotorshaft torques is a result of compensating errors  and the quality of the calculational code was not good at all! This clearly proves that validation and improvement of aerodynamic models needs detailed aerodynamic measurements and cannot be based on global loads.

          More information can be found in G. Schepers Engineering models in aerodynamics, PhD thesis, November 27th, 2012, Technical University of Delft, Netherlands https://repository.tudelft.nl/islandora/object/uuid%3A92123c07-cc12-4945-973f-103bd744ec87

          What are the specific benefits of the IEA Tasks on aerodynamics?

          A first benefit which should be mentioned is the fact that an IEA Task offers a platform to share experiences and knowledge on the very specialised field of aerodynamic modelling and measurements. All participating bodies in the previous aerodynamic IEA Tasks (14, 18, 20, 29) acknowledge that this leads to huge mutual benefits with enhanced knowledge levels at all parties.
          These shared insights and analyses from the Task partners improved the quality of the various experimental databases after which these databases could be provided as high level validation material for design codes to a countless number of partners in the IEA Tasks but also to third parties all over the world. This holds for the field measurements taken in IEA Tasks 14/18, the NASA-Ames wind tunnel measurements from Task 20, the Mexico wind tunnel measurements from Task 29 and the DanAero field measurements from Task 29. The resulting knowledge of uncertainties in design calculations from these validations help designers to assess the validity of their design calculations, and allows standardisation bodies to recalibrate safety factors in design standards. The measurements also led to fundamental model insights and aerodynamic understanding which clearly supported the improvement  of aerodynamic wind turbine models as implemented in design codes. This is illustrated by the proposition  from [1]   (i.e. a PhD thesis based on the results of IEA Task 14/18/20 and the first phase of Task 29)
          nowadays there isn’t a designer to find who would dare to design a wind turbine with the very basic aerodynamic modelling as applied in 1980’ [2)]

          More specific the figure illustrates how knowledge on aerodynamics, together with knowledge on other disciplines, play a role in assessing the cost of energy.

           

          The role of design codes (and aerodynamics) in assessment of LCOE (acknowledgement, Carlo Botasso, TUM)

          The Levelised Cost of Energy (LCOE) of wind energy is largely determined by the performance and capital costs, where capital costs are directly related to turbine loading. Both performance and loading are predicted with higher accuracy from the improved aerodynamic models. The cost model of FP7 INNWIND.EU shows that a combination of 5% increase in energy yield with a 12% decrease of the design loads of the turbine critical components and offshore substructure lead to a 10% LCoE reduction (conservative estimate). It is also important to realise that recommendations on optimal blade design and blade innovations, e.g. the optimal choice of airfoils or application of blade add-ons are important means for reducing the LCoE. These optimisations and innovations can only be succesful if the blade aerodynamics is understood.

          [1] Schepers J.G. Engineering models in aerodynamics, PhD thesis, November 27th, 2012, Technical University of Delft, Netherlands

          [2] Van Grol, H.J, Snel, H, Schepers J.G.(1990)European Wind Turbine Benchmark Exercise on Mechanical Loads, WTBE/ML, Energy Research Center of the Netherlands, ECN

          Why do we need aerodynamic research on wind turbines?

          It should be realized that upscaling turbines towards say 200-300m diameter is the most promising way to reduce cost of energy, in particular for offshore applications. This upscaling is possible only under the condition that such enormous rotors are feasible from a technical and economic point of view. However these huge rotor-blades are an enormous scientific and design challenge in particular due to the uncertainties from the aerodynamics. The results of the FP7 AVATAR project [1] have shown that the lack of coherence and the larger shear and veer which are inherent to those large wind turbines) challenge the modelling of aeroelastic response. An illustration of a modelling challenge is given in the figure below from [2]. It gives the extreme veer (i.e. the variation in wind direction with height) over the year 2015 at the location of Met Mast IJmuiden in the Dutch part of the North See. It shows that the maximum veer over the rotor plane of a 10 MW rotor (with diameter 220 meter) in this year is approximately 40 degrees! The modelling of such a large veer heavily violates the assumptions in the BEM theory (the aerodynamic work horse of industry). As a matter of fact BEM assumes no yaw misalignment at all and definitely no large variation of yaw angle over the rotor plane.

          Shear (left) and extreme veer (wind direction as function of height, right) from the year 2015 at location of Met Mast IJmuiden in the North Sea (dashed lines indicate lower and upper part of rotor plane and hub height of 10 MW turbine), from [2]

          Moreover this huge size in itself add complexity through large blade deflections and the need for thick airfoils which are very difficult to model. Task 47 will overcome these challenges so that  these large wind turbines can become a reality indeed as a means to reduce costs of Energy. Apart from that a thorough understanding of aerodynamics and aero-elastics straigthforwardly reduces the levelized cost of energy LCOE due to better load and performance predictions. As a conservative estimate a 10% reduction in LCOE is possible from better aerodynamic models.
          Finally the remark should be made that the history of wind energy aerodynamic research is still very young (say 30 years). Aerodynamic research in adjacent areas like airplane aerodynamics (or car aerodynamics) has a much longer history (> 100 years), see the figure.

          Incomplete airplane aerodynamics even after decades of research (Ackowledgement, Gijs van Kuik, TUDelft)

          This is not surprising since aerodynamics is a millennium prize problem, i.e. a problem which at the end of the last millennium was believed to be so complex that a significant part of the present millennium will be needed to solve it

          [1] G. Schepers et al Final report of the EU project AVATAR: Aerodynamic modelling of10 MW turbines February 2018, http://www.eera-avatar.eu/publications-results-and-links/

          [2] Schepers, J.G.; van Dorp, P; Verzijlbergh, R.; Jonker, H (2020) Aero-elastic loads on a 10 MW turbine exposed to extreme events selected from a year-long Large-Eddy Simulation over the North Sea Wind Energy Science, https://doi.org/10.5194/wes-2020-1

          .

          Why did Task 47 shift focus from field measurements to wind tunnel measurements and now back again to field measurements?

          In principle measurements in the field would be preferred above wind tunnel measurements, since such measurements can be done on representative full size turbines which avoids the inevitable scaling effects in a wind tunnel environment. Moreover the atmospheric conditions are representative to the conditions which are experienced on a commercial wind turbine. Still this stochastic atmosphere, though representative, makes interpretation of results complicated due to the unknown instantaneous inflow in the rotor plane which is the reason why wind tunnel measurements are important too. The stationary, known and homogeneous wind tunnel conditions facilitate the interpretation of measurement results and makes it possible to detect very subtle and small, briefly lived aerodynamic structures and events. In general terms it should be concluded that there are pro’s and con’s to both wind tunnel and field measurements. The best remedy to overcome these drawbacks is to combine the insights from full scale field measurements with those from wind tunnel measurements.  In other words it is not wind tunnel measurements OR field measurements but it is wind tunnel measurements AND field measurements. In a sound scientific approach these measurements need to be complemented with theoretical results.
          It should als be noted that measurement techniques have progressed in the last decades. This is amongst others true for the measurement of inflow where modern (LIDAR) measurement techniques give much more detail on the rotor inflow than the mast wind measurements in IEA Tasks 14/18. Moreover partners in the IEA Task work on the development and application of new innovative (pressure) sensors which were not available at the time of IEA Task 14/18.

          How is the cooperation with other IEA Tasks ensured?

          In the pre-decessor project IEA Task 29 several instruments were employed to ensure communication. It even resulted in a separate Work Package ‘Communication to other IEA Tasks’. The most succesful cooperation was found to be the appointment of activity leaders which participate in other IEA Tasks as well. This even led to a common Benchmarks on aero-acoustics with IEA Task 39 ’Silent wind turbine and a common Benchmark with Task 30 on the so-called Unaflow measurements. Through these benchmarks aerodynamic insights from Task 29 are fed into other IEA Tasks. Similar instruments will be employed in IEA Task 47

          You use a lot of acronyms, Mexico, New Mexico, Mexnext, what does it all mean?

          The Mexico project was carried out in 2006. It stands for Measurements and Experiments in Controlled Conditions. It was an EU project in which detailed aerodynamic measurements were carried out on a 4.5 meter diameter wind turbine placed in the German Dutch Wind Tunnel DNW. From the beginning this experiment was intended to be done in 2 shifts so that lessons learned from the first shift could be taken into account in the second shift. Budgetary constraints made that the second shift could be done in 2014 only. The name New Mexico was then found to be a funny name for this second shift.

          Mexnext refers to the phases 1 to 3 of IEA Task 29. It should be known that the Mexico and New Mexico project stopped as soon as the measurements were collected and there was no room to dive into the data. Therefore the analysis of data was done in a large cooperative effort within Task 29. As such Mexnext can be read as the follow-up(NEXT) activity of the (New)MEXico experiment

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