## Task 47 Work Plan and Objectives

Please find below our work plan and objectives

The Work Plan consists of 2 technical Work Packages. **WP1** and **WP2** are focused on experiments and calculations respectively whereas **WP3** ensures good cooperation with other IEA Tasks.

In WP1 and WP2 several calculations are performed. It is then important to know that the present consortium covers the entire spectrum of design models ranging from efficient low fidelity models as used in industry to high fidelity computational extensive models used by research institutes with a variety of intermediate models in between. In this way, a very good insight is obtained on how different models cope with the design of large wind turbines under real inflow.

The main goal of WP1 is to **share experiences in the specialistic field of detailed aerodynamic measurements**. Several new aerodynamic experiments are currently being initiated. This is true in Denmark, France, Germany, Italy, Netherlands, Switzerland, and the USA.

In the WP the experimental parties learn from each other about methods and techniques which work successfully and what should be prevented so that they all improve the quality of the experiments. Moreover, the measurement results will be shared with the consortium so that the theoretical partners get first-hand information from these unique new data. For example, unsteady pressure distribution at special events (standstill, heavy gusts) will provide much insight into the aerodynamics at such events and form the inspiration for theory development. Measurements from at least the DanAero experiment will be simulated under turbulent conditions.

Thereto it should be known that the first three phases of IEA Task 29 considered measurements at non-turbulent wind tunnel conditions. In the final phase, DanAero measurements in the field were simulated but mostly under steady time-averaged conditions. Obviously in cases of turbulent inflow a statistical evaluation e.g. an evaluation based on mean values as carried out in Task 29 is useful but it is equally important to analyze the development of forces over time. It was found that modeling the aerodynamic response at **turbulent** conditions leads to several additional complications which have a large impact on the loads and which are not or are poorly understood yet. Moreover, a major research effort is needed to ensure a consistent comparison procedure between low and high-fidelity models which is explained below and which forms part of WP2.

An even larger challenge, which forms the subject of WP1.2 lies in a consistent comparison between calculations and measurements. The wind speed in the DanAero experiment is measured at a mast some distance away from the turbine which may not form sufficient input for a comparison between calculations and measurements on a time series basis.

It is anticipated that 2 rounds of calculations are carried out where every round will consist of several iterations. Within IEA Task 29 much experience has been gained with modeling the Danaero turbine already so that a fully tested model description is available.

The first round is planned to start in August 2021 and lasts until October 2022.

**WP2** is defined around **turbulent calculations** on a large-scale **15 MW** wind turbine. Thereto a large variety of aerodynamic and aero-elastic models are available in the consortium. In this way, a very good insight is obtained into how different models cope with the design of 15MW wind turbines under real inflow and what the most important uncertainties are. These insights can be used in WP1 to define experiments that can answer these questions, even if the experiment is done on a smaller scale.

As an example calculations at parked storm conditions on a 15 MW RWT might lead to loads that depend heavily on the dynamic stall model used: one model may predict a stable solution, and another may predict an unstable solution leading to failure of the blades. If this becomes true, special attention is paid to the design of an experiment that measures dynamic stall effects at standstill. Another example is that the torsional flexibility of large blades might lead to unsteady aerodynamic effects. If this becomes true special attention needs to be paid to measure such effects.

It is noted that the setup and character of the calculations on the 15 MW RWT are very similar to the calculations in WP1. However, the present calculations are performed on the 15 MW RWT without measurements whereas WP1 carries out calculations on the DanAero turbine which are not only compared mutually but also with measurements. As explained in the description of WP1.2 for turbulent calculations attention needs to be paid to a consistent comparison procedure between low and high-fidelity models under turbulent conditions.

In 2021 and 2022 preparatory calculations are carried out which aim to establish the aerodynamic reference, i.e. a correct aerodynamic input so that each model will simulate the 15MW RWT in the follow-up tasks without trivial input errors. Thereto aerodynamic simulations will be carried out under relatively simple conditions, e.g. uniform steady flow, prescribed shear, prescribed gusts, etc.

Results from thrust and power (also on sectional level) will be compared until confidence is obtained on the correct input. Moreover, an aero-elastic Benchmark will be carried out which aims to gain confidence in the aero-elastic input. Thereto several aero-elastic properties (e.g. Eigen frequencies modes etc.) are compared. It is then expected that the turbulent calculations on the 15 MW RWT will start in 2022.

It is anticipated that 2 rounds of calculations are carried out.

In **WP3** the main achievements from Task 47 are communicated to other IEA Wind Tasks which have connections to aerodynamics and vice versa. It is anticipated that in the present IEA Task many participants will be active in other IEA Tasks and the most effective way of communication is seen to be the appointment of these participants as contact persons for other Tasks.

## IEA Tasks with relations to Task 47

The IEA tasks which are considered to have closest relation to aerodynamics are:

- IEA Task 19: ‘’Wind Energy in Cold Climates’’ (The connection to the present Task lies in models which can assess the aerodynamic effects of iced turbine blades)

- IEA Task 30 ‘’Comparison of Dynamic Computer Codes and Models for Offshore Wind Energy’’ (The connection to the present Task lies amongst others in a common Benchmark which was started up in Task 29 om the so-called Unaflow measurements, ie. wind tunnel measurements on an underground which simulates floating movements. The Benchmark is carried out by Task 30 and Task 29 participants and aerodynamic insights from Task 29 are fed into Task 30 and vice versa. The new Task wants to proceed with feeding Task 30 in the same way as Task 29

- IEA Task 31, ‘’Wakebench’’ (The connection to the present Task lies in the near wake which forms the starting point of the far wake considered in WakeBench. Moreover, the present Task will consider the turbine response to waked inflow with an impact on the loading whereas Wakebench considers the power output at wake inflow)

- IEA Task 37 ‘’Wind Energy Systems Engineering: Integrated R, D&D’’ (The connection to the present Task lies in aerodynamic models which are integrated into Task 37. Moreover, the 15 MW Reference Wind Turbine which is designed in Task 37 will be used reference turbines in WP2 )

- IEA Task 39 ‘’Quiet noise technologies’’ (The connection to the present Task lies in the improved understanding of aerodynamics which is input to the aero-acoustic models. A common Benchmark on aero-acoustic models has started up between Task 39 and Task 29 which can continue in the new Task)

- IEA Task 46 "Erosion of wind turbine blades". The connection lies in the fact that erosion of wind turbine blades has a large aerodynamic impact. Task 47 can help to understand this aerodynamic impact.

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