**5. Conclusions**

The article summarizes the observations made in frames of a numerical study of a small HAWT performance. The simulation was based on the reference experiment, performed on a prototype in wind tunnel conditions. The results of fluid flow assessment prove to underestimate the HAWT performance, which was attributed to the simplifications of the model, but a satisfactory qualitative agreement is found between simulation and experiment nonetheless.

Furthermore, thanks to one-way coupling FSI, it was possible to perform a structural assessment of the turbine. Firstly, stresses occurring in the blade during different operational load cases were inspected. The study proved that the structural integrity of CNC-milled blades is not threatened in its operating regions, and there are still high safety margins. Next, the study of deformations delivered an overview of potential blade twisting and bending due to the experienced loads. Under normal operating conditions of the assessed wind turbine, these additional deformations turned out to be negligible, with very little to no harm to blade aerodynamics.

The study proved that—in the context of small wind turbines—the FSI analysis may be an interesting choice not only for the strength analysis of non-orthodox materials but may also try to help estimate the influence of the blade deformation on rotor performance. Future plans include extending the simulation towards transient investigations in order to examine the fatigue influence on the blade endurance.

**Author Contributions:** Data curation, M.L. and P.C.; Investigation, P.C.; Supervision, D.O.; Writing – original draft, M.L., P.C. and D.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** The investigations have been performed under the research project POWR.03.02.00-00-I042/16-00 of the National Centre for Research and Development.

**Acknowledgments:** The authors would like to thank the GUST team for sharing the experience and data collected during the TU Delft Open Jet Facility wind turbine prototype testing.

**Conflicts of Interest:** The authors declare no conflict of interest.
