IEA Wind TCP

The kick-off meeting of Task 47 Turbinia was held online in three sessions of 2.5 hours on April 6, 8, and 9 2021 after which the project got into full swing. Several follow-up meetings took place online and on May 30 2022, the day before the Science of Making Torque conference, the first hybrid (personal/online) meeting will be held at TNO Delft. Moreover a second hybrid meeting was held at the University of Stuttgart at the end of November 2022.

Within WP1  several countries started to define detailed aerodynamic measurement programs and several new aerodynamic measurement technologies are developed and applied, e.g. MEMS-based pressure sensors, fiber optic pressure sensors, and pressure belts. Some first data are collected already amongst others at standstill conditions at high winds under vibrating conditions.

In order to share experiences in this specialized field of aerodynamic measurements, for the benefit of others use is made of the WeDoWind collaboration and knowledge sharing platform developed by the Eastern Switzerland University of Applied Sciences (OST). With this platform, it is possible to share knowledge, data, and code on issues related to aerodynamic measurements and simulations. Thereto several "discussion challenges" have been defined which are considered relevant subjects for further discussions in Task 47. Examples of challenges are: How to find the angle of attack in aerodynamic field experiments, how to compare (turbulent) simulations and measurements, how to do standstill measurements etc. Moderated workshops are organized for each challenge. These workshops are recorded and documented in a structured way on the WeDoWind platform. Now in a next step the experiences are reported in a so-called recommendation document on aerodynamic measurements so that they can form reference material for future users.

Moreover, a calculational case was defined around the DanAero experiment where the comparison is done on the basis of time series. Thereto, it should be noted that a ‘conventional’ comparison of statistical properties depends heavily on the random seed which is needed for the turbulent wind field generation. Comparison based on a time series basis turns out to be very challenging since the timing of results from lifting line codes, CFD codes, and measurements all need to be synchronized. Generally there is a reasonable agreement between calculational results and measurements and also between the calculational results mutually but generating representative wind from the meteorological mast measurements remains challenging in few of the relatively low resolution of meteorological sensors. Much potential is seen for time series comparisons with  the new experiments in TURBINIA which apply LIDAR. The much higher resolution of LIDAR wind speed measurements makes it possible to generate turbulent wind speed which will agree better with reality.

Still some important differences remain which could be related to the modelling of non-uniform inflow which becomes more important for large turbines. Therefore a new shear case will be defined which then will be calculated by CFD codes as well.

Within WP2 a first preparatory case is defined for the IEA 15-MW Reference Wind Turbine which aims to check the correct aerodynamic and aero-elastic input so that trivial input errors are eliminated in the follow-up calculational rounds. Thereto, aerodynamic simulations are carried out under relatively simple conditions, with uniform steady inflow. The calculations are done with lifting line models but also with CFD models.  activities on the 15-MW Reference Wind Turbine are coordinated with IEA Task 37. The turbine model for lifting line codes was available from Task 37 where it is noted that the simplifications led to some deviations of the original turbine model, e.g. the axi-symmetric conditions require the tilt angle to be zero which then in turn leads to different tower height, tower overhang etc.

The input for CFD codes was not available yet but it was generated in Task 47.

Generally speaking the agreement between results is very reasonable. An important finding is the large torsion angle on the blade of such a 15 MW turbine, which is found to be in the order of 2 degrees at the tip even for a relatively low wind speed of 7.5 m/s. Such a large torsion angle obviously has a significant impact on the performance, the control and the loads which makes the accurate modelling of it very important and which implies that the relative large differences in calculational results needs to be understood.

Some final iterations are made to these preliminary calculations and then in a next step calculations on the 15 MW Reference wind turbine are carried out under turbulent wind.