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ABSTRACT. -The commercial exploitation of kinetic energy from tidal current involves deploying multiple turbines constituting a park or a farm. The turbines located within the park suffer from the disrupted flow due to the wake of machines located further upstream. This will potentially alter their performance. The evolution of the wake is influenced by the environment and by the machine. A two-dimensional model of a vertical axis turbine of Darrieus type was performed to investigate the flow within and downstream the turbine. The relative influences on the characteristics of the wake of two parameters were evaluated: the speed of the upstream flow and the Tip speed ratio λ. The latter seems to be dominant for the lack of speed while the level of turbulence is a function of the two parameters setting.Key-words: Marine Renewable Energy, Vertical axis current turbine, numerical simulation, wake, turbulence, Marine current turbine farm. Etude numérique du sillage d'une hydrolienne à axe verticalRÉSUMÉ. -L'exploitation de l'énergie cinétique des courants de marée impliquera le déploiement de plusieurs hydroliennes constituant un parc. Les hydroliennes se trouvant au sein de ce parc subiront le flux perturbé du sillage des machines situées plus en amont, altérant potentiellement leurs performances. L'évolution du sillage est influencée par l'environnement et la machine. Une modélisation bidimensionnelle d'une hydrolienne à axe verticale de type Darrieus a été réalisée pour étudier l'écoulement dans et en aval de la turbine. L'influence relative sur les caractéristiques du sillage de deux paramètres a été évaluée : la vitesse de l'écoulement amont et la vitesse réduite de l'hydrolienne. La vitesse réduite λ semble être le paramètre dominant pour le déficit de vitesse alors que le niveau de turbulence est une fonction des deux paramètres.

The present study aims to develop a model to simulate in 2 dimensions, the motion of the fluid and of the loaded Darrieus turbine without imposing the rotational speed. A resistive torque has been added to account for the load of a generator. Experimental and numerical studies were conducted and presented here. The experiment was setup in the air first, on a wind turbine for reason of convenience. The simulations were made with Fluent (v14) for which a User Defined Function was developed. Then the experimental conditions were reproduced numerically for three cases. The study focuses on the determination of a factor (f) giving the relationship between the experimental and the simulated resistive torque in 2 dimensions. The results are quite satisfying in this preliminary study as they demonstrate that the model developed works well. Some improvement has to be made to refine the value of f .