Vicoter (www.vicoter.it) is a consulting company founded in 2009, operating in the field of static and dynamic measurements of mechanical structures. Its organizational flexibility, its instrumentation, as well as its wide-ranging skills, make Vicoter the most suitable partner for solving unusual problems and research projects for many larger companies.
In a consolidated collaboration with SEVA S.r.l. (http://www.sevasrl.it/index.php/it/), a company operating in the renewable energy sector, Vicoter carried out in July 2022 a test campaign on a wind turbine blade, more than 20 meters long, in order to obtain information for the development of reliable finite element models (FEM) to be used in estimating the generators performance. Tests were carried out at the SEVA S.r.l. site, in Novi Ligure (AL), Italy, with the blades fixed to the ground by means of an ad-hoc designed supporting structure.
The purpose of the test campaign was twofold: to determine the stiffness of the structures and to determine their aerodynamic profiles.
A photogrammetric technique was used to satisfy both requests.
Photogrammetry (https://en.wikipedia.org/wiki/Photogrammetry) is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images. This test methodology is more and more adopted in recent years in the field of displacement measurements, thanks to its relative simplicity and low cost. In Vicoter’s applications, the structure is photographed from multiple angles and images are processed using a special software capable of determining the coordinates of selected points. Using ad-hoc printed markers placed on the structure, the number of identified points can be increased, as well as the accuracy of their position. In static tests, the blade was scanned before and after the application of a static load. Load was applied in five stations along the blades, for a total of more than one ton. Thanks to the comparison between the photogrammetric measurements obtained on the undeformed and on the deformed structure, it was possible to measure both the displacement and the rotation of the six investigated sections. It should be noted that, by appropriately positioning the reference markers, it was possible to purify the measurements by the intrusiveness of the support structure, i.e., to obtain the structural deformations free from the constraint ones. Both flap and lag stiffness were identified by repeating the acquisitions, after rotating each blade 90 °.
The blade aerodynamic profiles were measured in five sections with the same photogrammetric technique. In particular, for this request, markers were placed both on the front side and on the back side of the blade, and to photo sets were acquired. Then, using specific measurement points visible in both the photo sets, the sections were reconstructed.
An example of the obtained results is shown in the following figure.