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No description available.

No description available.

No description available.

Experimental research has been completed using a custom designed and built 4m diameter wind turbine in a university operated wind facility. The primary goals of turbine testing were to determine the power production of the turbine and to apply the particle image velocimetry (PIV) technique to produce flow visualization images and velocity vector maps near the tip of a blade. These tests were completed over a wide range of wind speeds and turbine blade rotational speeds. This testing was also designed to be a preliminary study of the potential for future research using the turbine apparatus and to outline it's limitations. The goals and results of other large scale turbine tests are also briefly discussed with a comparison outlining the unique aspects of the experiment outlined in this thesis. Power production tests were completed covering a range of mean wind speeds, 6.4 m/s to 11.1 m/s nominal, and rotational rates, 40 rpm to 220 rpm. This testing allowed the total power produced by the blades to be determined as a function of input wind speed, as traditionally found in power curves for commercial turbines. The coefficient of power, Cp, was determined as a function of the tip speed ratio which gave insight into the peak power production of the experimental turbine. It was found, as expected, that the largest power production occurred at the highest input wind speed, 11.1 m/s, and reached a mean value of 3080 W at a rotational rate of 220 rpm. Peak Cp was also found, as a function of the tip speed ratio, to approach 0.4 at the maximum measurable tip speed ratio of 8. Blade element momentum (BEM) theory was also implemented as an aerodynamic power and force prediction tool for the given turbine apparatus. Comparisons between the predictions and experimental results were made with a focus on the Cp power curve to verify the accuracy of the initial model. Although the initial predictions, based on lift and drag curves found in Abbot and Von Doenhoff (1959), were similar to experimental results at high tip speed ratios an extrapolation of the data given by Hoffman et al. (1996) was found to more closely match the experimental results over the full range of tip speed ratios. Finally PIV was used to produce flow visualization images and corresponding velocity maps of the chord-wise air flow over an area at a radius ratio of 0.9, near the tip of a blade. This technique provided insight into the flow over a blade at three different tip speed ratios, 4, 6 and 8, over a range of wind speeds and rotational rates. A discussion of the unique aspects and challenges encountered using the PIV technique is presented including: measuring an unbounded external flow on a rotating object and the turbulence in the free stream affecting the uniform seeding and stability of the flow.

Experimental research has been completed using a custom designed and built 4m diameter wind turbine in a university operated wind facility. The primary goals of turbine testing were to determine the power production of the turbine and to apply the particle image velocimetry (PIV) technique to produce flow visualization images and velocity vector maps near the tip of a blade. These tests were completed over a wide range of wind speeds and turbine blade rotational speeds. This testing was also designed to be a preliminary study of the potential for future research using the turbine apparatus and to outline it's limitations. The goals and results of other large scale turbine tests are also briefly discussed with a comparison outlining the unique aspects of the experiment outlined in this thesis. Power production tests were completed covering a range of mean wind speeds, 6.4 m/s to 11.1 m/s nominal, and rotational rates, 40 rpm to 220 rpm. This testing allowed the total power produced by the blades to be determined as a function of input wind speed, as traditionally found in power curves for commercial turbines. The coefficient of power, Cp, was determined as a function of the tip speed ratio which gave insight into the peak power production of the experimental turbine. It was found, as expected, that the largest power production occurred at the highest input wind speed, 11.1 m/s, and reached a mean value of 3080 W at a rotational rate of 220 rpm. Peak Cp was also found, as a function of the tip speed ratio, to approach 0.4 at the maximum measurable tip speed ratio of 8. Blade element momentum (BEM) theory was also implemented as an aerodynamic power and force prediction tool for the given turbine apparatus. Comparisons between the predictions and experimental results were made with a focus on the Cp power curve to verify the accuracy of the initial model. Although the initial predictions, based on lift and drag curves found in Abbot and Von Doenhoff (1959), were similar to experimental results at high tip speed ratios an extrapolation of the data given by Hoffman et al. (1996) was found to more closely match the experimental results over the full range of tip speed ratios. Finally PIV was used to produce flow visualization images and corresponding velocity maps of the chord-wise air flow over an area at a radius ratio of 0.9, near the tip of a blade. This technique provided insight into the flow over a blade at three different tip speed ratios, 4, 6 and 8, over a range of wind speeds and rotational rates. A discussion of the unique aspects and challenges encountered using the PIV technique is presented including: measuring an unbounded external flow on a rotating object and the turbulence in the free stream affecting the uniform seeding and stability of the flow.

Les tourbillons hélicoïdaux générés derrière les rotors sont étudiés. Pour les générer, une méthode basée sur le couplage entre la technique de la ligne active et un solveur des équations de Navier-Stokes (ENS), incompressibles et tridimensionnelles, a été développée. Elle consiste à modéliser la pâle par son équivalent de forces volumiques. Les équations, écrites en coordonnées cylindriques, sont résolues par un schéma de différences finies, écrit en parallèle. La méthode est d'ordre deux en temps et en espace. Le solveur des ENS a été validé par la reproduction des taux de croissance d'un écoulement de jet, instable, trouvés par la théorie d'instabilité linéaire. La comparaison avec des données expérimentales a montré que la méthode prédit bien l'aérodynamique de la pâle. Ensuite, le tourbillon de bout de pâle a été, en particulier, caractérisé. La vorticité et la vitesse azimutale ont été trouvées auto-similaire et la taille du coeur suit asymptotiquement la loi de diffusion linéaire 2D. Un modèle simple du coeur du tourbillon a été proposé. La présence d'une vitesse axiale dans le coeur du tourbillon a été montrée et a été caractérisée en fonction du rapport de vitesse au bout de la pâle. Finalement, une étude de stabilité du tourbillon a été faite en utilisant une vitesse angulaire variable pour perturber l'écoulement. Les taux de croissances des modes les plus instables sont en bon accord avec celui de l'instabilité d'appariement 2D des tourbillons. Trois types de modes ont été identifiés en fonction de la fréquence des perturbations et ont été trouvés similaires aux modes décrits par la théorie et aussi trouvés, précédemment, par l'expérience. / This present work is aimed to study helical vortices encountered in the wakes of rotating elements. For this, the generation of a helical wake of a one-bladed-rotor in a laminar velocity field, is simulated by the actuator line method. This method is a coupling of a Navier-Stokes (NS) solver with the Actuator Line Method where the blade is replaced by the body forces. This method has been implemented in a finite difference code, that we have written in parallel to solve the 3D incompressible NS equations written in cylindrical coordinates. The order of accuracy of the method is two both in time and space. The NS solver was validated comparing growth rates of an unstable jet, found numerically, and those of linear instability theory. A good agreement was found. A good agreement was also found comparing numerical results to analytical formulations and experimental data. It was shown that the method predicts well the blade aerodynamics . Then, the helical tip vortex is characterized for different Reynolds numbers and Tip Speed Ratios. The vorticity and the azimuthal velocity were found self-similar and the vortex core follows asymptotically the linear 2D diffusion law. A simple model for the helical vortex core was proposed. The presence of an axial velocity inside the vortex core was highlighted. Then, a stability study of the helical tip vortex was done using an angular velocity dependent on time to perturb the flow. The largest growth rates were found in good agreement with those of the (2D) pairing instability. Three types of modes were identified based on the perturbation frequency. The results are similar to those found in previous analytical and experimental works.