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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Sep 2019

Submitted as: research article | 18 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).

Investigations of aerodynamic drag forces during structural blade testing using high fidelity fluid-structure interaction

Christian Grinderslev1, Federico Belloni1,2, Sergio González Horcas1, and Niels N. Sørensen1 Christian Grinderslev et al.
  • 1Department of Wind Energy, Technical University of Denmark, Risø Campus, 4000, Roskilde
  • 2Blade Test Centre A/S, Landdybet 10, 9220, Aalborg

Abstract. Aerodynamic loads on wind turbine blades that are tested for fatigue certifications, need to be known for planning and defining test loads beforehand. It is known that the aerodynamic forces, especially drag, are different for tests and operation, due to the entirely different flow conditions. In test facilities, a vibrating blade will move in and out of its own wake increasing the drag forces on the blade. This is not the case in operation. To study this special aerodynamic condition present during experimental tests, numerical simulations of a wind turbine blade during pull-release tests were conducted. High fidelity three dimensional computational fluid dynamics methods were used throughout the simulations. By this, the fluid mechanisms and their impact on the moving blade are clarified and through the coupling with a structural solver, the fluid-structure interaction is studied. Results are compared to actual measurements from experimental tests, verifying the approach. It is found that the blade experiences a high drag due to its motion towards its own whirling wake, resulting in an effective drag coefficient of approximately 5.3 for the 90 degree angle of attack. This large drag coefficient was implemented in a fatigue test load simulation, resulting in a significant decrease of moment along the blade, leading to less load applied than intended. The confinement from the test facility did not impact this specific test setup, but simulations with longer blades could possibly yield different conclusions. To the knowledge of the authors, this investigation including three dimensional effects, structural coupling and confinement is the first of its kind.

Christian Grinderslev et al.
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Status: open (extended)
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Christian Grinderslev et al.
Christian Grinderslev et al.
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Short summary
This study focusses on coupled computational fluid and structural dynamics simulations of a dynamic structural test of a wind turbine blade, as performed in laboratories. It is found that drag coefficients used for simulations, when planning fatigue tests, underestimate the air resistance to the dynamic motion which the blade undergoes during tests. This can result in the forces applied to the blade actually being lower in reality during tests than what was planned, if not corrected for.
This study focusses on coupled computational fluid and structural dynamics simulations of a...