Cette thèse vise à étudier les effets de la transition laminaire - turbulent et du contrôle actif de l’angle de calage des pales sur les performances de l’hydrolienne à axe transverse SHIVA (Système Hydrolien Intelligent à Variation d’Angle) développée à l’institut de Recherche de l’Ecole-Navale (IRENav). L’écoulement transitionnel autour d’un hydrofoil est, d’abord étudié en comparant des résultats expérimentaux et numériques. Les résultats expérimentaux ont été obtenus dans le tunnel hydrodynamique de l’IRENav. La transition s’effectue par un mécanisme de bulbe de séparation laminaire. Les comparaisons sont fondées sur l’analyse locale des pressions, des profils de vitesse dans la zone du bulbe de séparation laminaire et sur l’analyse des portances, traînées et moments mesurés sur un profil fixe et en mouvement de tangage forcé. Des calculs RANS 2D, avec et sans modèle de transition (ɣ— Reo), RANS 3D et LES 2.5D ont été menés afin de comparer les approches et évaluer la précision des simulations. L’étude montre que le modèle de transition ɣ — Reo améliore nettement les résultats obtenus par rapport à un modèle tout turbulent (k — w SST) dans le cas d’un écoulement transitionnel. L’influence de la transition laminaire - turbulent sur les performances de la turbine SHIVA est ensuite étudiée en comparant les résultats de calculs effectués avec et sans modèle de transition. L’approche est bidimensionnelle. L’utilisation du modèle de transition est intéressante au paramètre d’avance ʎ = 2 pour lequel les pales subissent un décrochage dynamique important. Le développement du tourbillon de bord d’attaque, favorisé par le modèle de transition, permet en effet une meilleure prédiction du décrochage. Les valeurs de ʎ supérieures sont moins concluantes du fait de la prédiction d’une tramée trop faible par le modèle de transition. Enfin, l’influence du contrôle actif du calage des pales sur les performances de la turbine est étudiée au point de fonctionnement optimal de la turbine ʎ = 3. Des lois de calage avancées sont développées, permettant d’agir indépendamment sur la moitié amont ou aval de la turbine. La meilleure loi testée permet une augmentation du coefficient de puissance de 34% tout en lissant la répartition du couple. / This work studies the laminar-turbulent transition and the pitch control effects on the performances of a vertical axis tidal turbine (SHIVA) developed at the French naval academy research institute. Firstly, experimental and numerical results are compared to study the transitional flow around a hydrofoil. The experiments were carried out in the hydrodynamic tunnel of the French naval academy research institute and the laminar-turbulent transition was triggered by a laminar separation bubble mechanism. Comparisons are based on the local analysis of pressure data and velocity profiles in the vicinity of the laminar separation bubble. Lift, drag and moment coefficients measured on a fixed hydrofoil and on a hydrofoil undergoing a pitching movement are also used for comparison. 2D RANS calculations carried out with or without a transition modal (ɣ — Reo), 3D RANS calculations and 2.5D LES calculations were run so as to assess the accuracy of each type of simulation. This study shows that the ‘y Reo transition modal clearly improves the accuracy of the results compared to a fully turbulent turbulence model (k— w SST) when considering a transitional flow. The influence of the laminar-turbulent transition on the performance of the SHIVA turbine is then studied. Results of 2D calculations run with and without transition model are compared. The use of the transition modal is relevant at the tip speed ratio value ʎ = 2 for which the blades undergo dynamic stall. The transition modal leads to a better prediction of the leading edge vortex development and then allows a better prediction of the dynamic stall. The use of the transition model at higher ʎ values is less relevant since the transition modal appears to predict a drag too low. Finally, the effect of the pitch control on the SHIVA turbine performance is .studied at ʎ = 3, for which the power coefficient is the highest. Advanced pitching laws are developed to modify the blades’ angle of attack independently on the upstream and downstream halves of the turbine. The best pitching law tested in this study leads to an improvement of the power coefficient by 34% and smooths the torque distribution.

Shear layer development over a NACA 0018 airfoil at a chord Reynolds number of 100,000 was investigated experimentally. The effects of experimental setup and analysis tools on the results were also examined. The sensitivity of linear stability predictions for measured separated shear layer velocity profiles to both the analysis approach and experimental data scatter was evaluated. Analysis approaches that are relatively insensitive to experimental data scatter were identified. Stability predictions were shown to be more sensitive to the analysis approach than to experimental data scatter, with differences in the predicted maximum disturbance growth rate and corresponding frequency of approximately 35% between approaches. A parametric study on the effects of experimental setup on low Reynolds number airfoil experiments was completed. It was found that measured lift forces and vortex shedding frequencies were affected by the end plate configuration. It was concluded that the ratio of end plate spacing to projected model height should be at least seven, consistent with the guideline for circular cylinders. Measurements before and after test section wall streamlining revealed errors in lift coefficients due to blockage as high as 9% and errors in the wake vortex shedding frequency of 3.5%. Shear layer development over the model was investigated in detail. Flow visualization images linked an observed asymmetry in wake velocity profiles to pronounced vortex roll-up below the wake centerline. Linear stability predictions based on the mean hot-wire profiles were found to agree with measured disturbance growth rates, wave numbers, and streamwise velocity fluctuation profiles. Embedded surface pressure sensors were shown to provide reasonable estimates of disturbance growth rate, wave number, and convection speed for conditions at which a separation bubble formed on the airfoil surface. Convection speeds of between 30 and 50% of the edge velocity were measured, consistent with phase speed estimates from linear stability theory.

Shear layer development over a NACA 0018 airfoil at a chord Reynolds number of 100,000 was investigated experimentally. The effects of experimental setup and analysis tools on the results were also examined. The sensitivity of linear stability predictions for measured separated shear layer velocity profiles to both the analysis approach and experimental data scatter was evaluated. Analysis approaches that are relatively insensitive to experimental data scatter were identified. Stability predictions were shown to be more sensitive to the analysis approach than to experimental data scatter, with differences in the predicted maximum disturbance growth rate and corresponding frequency of approximately 35% between approaches. A parametric study on the effects of experimental setup on low Reynolds number airfoil experiments was completed. It was found that measured lift forces and vortex shedding frequencies were affected by the end plate configuration. It was concluded that the ratio of end plate spacing to projected model height should be at least seven, consistent with the guideline for circular cylinders. Measurements before and after test section wall streamlining revealed errors in lift coefficients due to blockage as high as 9% and errors in the wake vortex shedding frequency of 3.5%. Shear layer development over the model was investigated in detail. Flow visualization images linked an observed asymmetry in wake velocity profiles to pronounced vortex roll-up below the wake centerline. Linear stability predictions based on the mean hot-wire profiles were found to agree with measured disturbance growth rates, wave numbers, and streamwise velocity fluctuation profiles. Embedded surface pressure sensors were shown to provide reasonable estimates of disturbance growth rate, wave number, and convection speed for conditions at which a separation bubble formed on the airfoil surface. Convection speeds of between 30 and 50% of the edge velocity were measured, consistent with phase speed estimates from linear stability theory.

No description available.

Vortex generator jets (VGJs) have been found to be an effective method of active separation control on the suction side of a low pressure turbine (LPT) blade at low Reynolds numbers. The flow mechanisms responsible for this control were studied and documented in order to provide a basis for future improvements in LPT design. Data were collected using a stereo PIV system that enabled all three components of velocity to be measured. Steady VGJs were injected into a laminar boundary layer on a flat plate (non-separating boundary layer) in order to more fully understand the characteristics and behavior of the produced vortices. Both normal (injected normal to the wall) and angled (injected at 30° pitch and 90° skew angles to the freestream) jets were studied. The steady jets were found to create vortices that swept the low momentum fluid up from the boundary layer while transporting high momentum freestream fluid towards the wall, a phenomenon that provides the ingredients for flow control. Pulsed VGJs were then injected on a flat plate with an applied adverse pressure gradient equivalent to that experienced by a commonly tested LPT blade. This configuration was used to study the effectiveness of the flow control exhibited by both normal and angled jets on a separating boundary layer. Time averaged results showed similar boundary layer separation reduction for both normal and angled jets; however, individual characteristics suggested that the control mechanism of the two injection angles is distinct. Steady and pulsed VGJs were then applied to a new aggressive LPT blade design to explore the effect of the jets on a separating boundary layer along the curved blade surface. Steady injection provided flow control through freestream entrainment, while pulsed jets created a two-dimensional, spanwise disturbance that reduced the separated area as it traveled downstream. A detailed fluid analysis of the uncontrolled flow around the blade was performed in order to identify the separation and reattachment points and the area of transition. This information was used as a basis for comparison with the VGJ cases to determine flow control effectiveness.