Étude des interactions entre deux hydroliennes à axe horizontal alignées avec l'écoulement

Les fermes d'hydroliennes de seconde génération sont des fermes dans lesquelles les interactions négatives, c'est-à-dire susceptibles de détériorer les performances des hydroliennes en aval, sont inévitables. Ceci est dû au fait que de nouvelles rangées d'hydroliennes doivent être ajoutées à une ferme de première génération afin d'augmenter sa capacité. Ces nouvelles rangées se situent inéluctablement dans le sillage des rangées précédentes et leur performance peut alors être profondément modifiée. Afin de mettre ces interactions en évidence, des essais expérimentaux ont été réalisés dans le bassin de l'IFREMER de Boulogne-Sur-Mer, sur des prototypes d'hydroliennes à l'échelle 1/30ème. Dans cette étude, nous nous concentrons sur l'interaction élémentaire de deux hydroliennes à axe horizontal, alignées l'une derrière l'autre avec l'écoulement. L'évolution des coefficients de puissance et de traînée en fonction de la vitesse de rotation de l'hydrolienne aval sont présentés afin de déterminer son efficacité. Pour cela, nous comparons les performances de l'hydrolienne aval aux performances de référence obtenues sur une hydrolienne seule. Par ailleurs, nous exposons des cartes de vitesse axiale, d'intensité turbulente et de cisaillement dans le sillage des hydroliennes afin d'expliquer leur comportement. Nous considérons une large gamme de distances, allant de deux à douze diamètres, entre les deux hydroliennes. D'autre part, nous étudions deux conditions d'intensité turbulente ambiante, à savoir 5% et 25%. Nous mettons en évidence l'influence de ce paramètre sur le comportement des hydroliennes et ainsi sur les effets d'interaction. En particulier, il apparaît clairement que des taux d'intensité turbulente élevés dans l'écoulement amont favorisent la dissipation des effets de sillage et offrent alors un meilleur compromis entre l'espacement entre les hydroliennes et leur performance individuelle

Tidal Energy Round Robin Tests: A Comparison of Flow Measurements and Turbine Loading

A Round Robin Tests program is being undertaken within the EC MaRINET2 initiative. This programme studies the used facility influence can have on the performance evaluation of a horizontal axis tidal turbine prototype when it is operated under wave and current conditions. In this paper, we present the design of experiments that is used throughout the work programme and the results related to the flow characterisation obtained at the Ifremer wave and current circulating tank, the Cnr-Inm wave towing tank and the ocean research facility FloWave. These facilities have been identified to provide adequate geometric conditions to accommodate a 0.724 m diameter turbine operating at flow velocities of 0.8 and 1.0 m/s. The set-up is replicated in each of the facilities with exemption of the amount of flow measuring instruments. Intrinsic differences in creating wave and currents between facilities are found. Flow velocities are up to 10% higher than the nominal values and wave amplitudes higher than the target values by up to a factor of 2. These discrepancies are related to the flow and wave generation methods used at each facility. When the flow velocity is measured besides the rotor, the velocity presents an increase of 8% compared to the upstream measurements

MaRINET2 Tidal Energy Round Robin Tests—Performance Comparison of a Horizontal Axis Turbine Subjected to Combined Wave and Current Conditions

This Round Robin Test program aims to establish the influence of the combined wave and current effect on the power capture and performance of a generic tidal turbine prototype. Three facilities offering similar range of experimental conditions have been selected on the basis that their dimensions along with the rotor diameter of the turbine translate into low blockage ratio conditions. The performance of the turbine shows differences between the facilities up to 25% in terms of average power coefficient, depending on the wave and current cases. To prevent the flow velocity increasing these differences, the turbine performance coefficients have been systematically normalized using a time-average disc-integrated velocity, accounting for vertical gradients over the turbine swept area. Differences linked to blockage effects and turbulence characteristics between facilities are both responsible for 5 to 10% of the power coefficient gaps. The intrinsic differences between the tanks play a significant role as well. A first attempt is given to show how the wave-current interaction effects can be responsible for differences in the turbine performance. In these tanks, the simultaneous generation of wave and current is a key part often producing disruptions in both of these flow characteristics

VIV and WIO using wake oscillator. Comparison on 2D response with experiments.

AbstractExperimental results are used to validate a 2D phenomenological model of the near wake based on Van Der Pol wake oscillators, which is the first one which describes the 2D motion of a cylinder in its transversal plan. In the case of a single cylinder, experimental and numerical results are in relatively good agreement. Those first results show that the proposed model can be used as a simple computation tool in the prediction of 2D VIV effects

Wake effects characterization using wake oscillator model. Comparison on 2D response with experiments

A model using wake oscillators is developed to predict the 2D motion in a transverse plan of two rigid cylinders in tandem arrangement. This model of the wake dynamics is validated with experimental data from previous trials which took place at the Ifremer flume tank in Boulogne-sur-Mer, France. The agreement between the model and the experimental results allows using this model as a simple computational tool in the prediction of 2D Vortex-Induced Vibrations (VIV) and, after some futher developments, Wake-Induced Oscillations (WIO) effects

Determination of the Response Amplitude Operator of a tidal turbine as a spectral transfer function

A transfer function determination method is proposed in this study to predict the unsteady fluctuations of the performance of a tidal turbine model. This method is derived from the Response Amplitude Operator (RAO) applied in the offshore industry to predict linear wave-induced loads on large structures. It is based on a spectral approach and requires the acquisition of a turbine parameter (e.g. torque, thrust, power or root-blade force) in synchronization with an upstream flow velocity measurement. On the frequency range where the causality between these two signals is proven, the transfer function is established using the ratio between the cross-spectral density and the spectral density of the incoming velocity.The linearity is verified using the coherence function, which shows validity for the turbine power in the lowest frequencies only. This transfer function is then used to reconstruct the power fluctuations which is compared to the recorded one for a particular flow condition with bathymetry generated turbulence. The result shows the dependence on the accurate location of the velocity measurement point used for the reconstruction. This point must exactly correspond to the expected turbine location, i.e. where the turbine response needs to be processed. Bearing in mind its limits, the method can be used to predict the loadings of extreme events on the turbine structure and the performance variations corresponding to the unsteady characteristics of a turbulent flow, for a better grid integration

Experimental study of coherent flow structures past a wall-mounted square cylinder

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