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4th Symposium on OpenFOAM in Wind Energy May 2-4, 2016, Delft, the Netherlands
* PhD Candidate, Department of Mechanical Engineering, Politecnico di Milano, [email protected] † Researcher, Department of Mechanical Engineering, Politecnico di Milano, [email protected].
Application of the actuatorline model for floating wind
turbine simulations
I.Bayati, M.Belloli, L.Bernini*, P.Schito†, A.Zasso Politecnico Milano, Milano, Italy
The aim of this work is the application of the Polimi actuatorline code for floating wind turbine aerodynamic simulation.
A wide dataset of wind tunnel measurement become recently available within the Lifes50+ project. This European project will develop next generation substructures for floating off-shore wind turbines. In order to validate the state of the art wind turbine aerodynamics codes Polimi performed in February 2016 a series of tests on a 1/75 scale model of the DTU 10 MW wind turbine. The unsteady measurement were gathered with a 2 degree-of-freedom test rig, capable of imposing the displacements at the base of the model, providing the surge and pitch motion of the floating offshore wind turbine scale model.
a) b) Figure 1 a) Wind tunnel setup; b) unsteady measured thrust (continuous line:steady results)
Polimi is currently working on the first comparison of the experimental results with some commonly used aerodynamic code based on BEM theory, however it is also interesting to evaluate the performance of more advanced aerodynamic models.
In particular, the authors had developed during the last four years a CFD tool for wind turbine rotor aerodynamics based on the actuatorline model [refs]. Polimi actuatorline, hereafter AL, showed some good results in steady comparison with previous wind tunnel data, Figure 2 shows
4th Symposium on OpenFOAM in Wind Energy May 2-4, 2016, Delft, the Netherlands
2
performance and wake reconstruction for an experimental test campaign on a commercially available 3MW wind turbine.
a) b) Figure 2 AL steady results comparison with experimental data. a) turbine performance (blue line: AL, red line: wind tunnel; b)
turbine wake (continuous line: AL, dashed line: wind tunnel)
The core part of this work is the modification of the AL code in order to permit the imposed motion simulation. Avoiding the use of body fitted mesh makes the AL the best candidate for simulation with the motion of the turbine structure.
Moreover the driving idea for this work effort is that the unsteadiness in the measured rotor thrust and torque does not derive from local blade unsteady behavior but rather from the rotor wake dynamics. The idea is that the induction factors cannot be considered as time-invariable, but they must be strongly dependent of the wake temporal response to the unsteady turbine motion. Since AL is developed in the CFD environment, the wake dynamics is inherently very well computed assuming that the rotor thrust and torque are correctly calculated from the polar table lookup.
