ABSTRACT A PARAMETRIC INVESTIGATION OF TIP INJECTION FOR ACTIVE TIP VORTEX CONTROL Dedekarginoglu, Riza Can M.Sc., Department of Aerospace Engineering Supervisor :Asst. Prof. Dr. Oguz Uzol December 2010, 79 pages Wing tip vortex is a challenging phenomenon that reduces the lift generation at the tip region of the wing. For aerial vehicles, several methodologies were presented for the sake of controlling vortices and alleviating effects of tip loss. In this study, the effect of wing tip injection on wing tip vortex structure was investigated computationally. A NACA0015 profile rectangular wing was employed with an aspect ratio of 3, at a free stream Reynolds number of 67000. 10 identical ejection holes along the wing were prepared chordwise to provide cross sectional air flow in order to determine the net effect of ejection over wing tip vortices and wake flow field. Study setup consists of a wind tunnel that is 1.6m long, 0.6m wide and 0.6m high, which the wing is attached to one side of it as a cantilever beam. Chord length of the wing is 0.1m and span is 0.3m. A constant free stream air flow is maintained with 10 m/s of velocity. Computer aided drawing (CAD) and grid generation were carried out using commercial tools. Whole setup was drawn using Rhinoceros. Surface mesh was created using ANSYS Gambit, ANSYS T-Grid software was used for generating the viscous mesh over the wing and finally for volume mesh ANSYS Gambit was utilized once more. FLUENT was chosen to be the flow solution tool with k-&omega / SST turbulence model. For 3 different angles of attack cases, respectively, 4&deg / , 8&deg / and 12&deg / , several injection scenarios were defined. There are 3 steady injection cases for each angle of attack case namely, no injection case, uniform injection case, triangular waveform injection case where there is no injection at the leading edge tip whereas there is injection which is equal to the uniform injection velocity at the trailing edge tip. Moreover there are 5 additional scenarios for 8&deg / angle of attack case that are, sinusoidal waveform injection case which consists of a chordwise velocity distribution shape that is a quarter sinus wave where maximum injection velocity is the same as the uniform velocity, reverse triangular waveform injection case where injection velocities were reversed with respect to triangular waveform case, two cases consisting of angled injections having both +15&deg / and -15&deg / with respect to the flapping axis of the wing. The effect of tube walls on the jet injection was neglected for all cases, therefore for the last case, in order to simulate pipe flow, a case is provided with uniform injection velocity. In that way, regardless of the solution method, a parametric study was performed. Considering each case, non-dimensional 3-axis velocity components, turbulent kinetic energy, vorticity magnitude, pressure, lift and drag values were computed and having the exactly same cases as an experimental study for 8&deg / angle of attack, a comparison of aerodynamic data series was presented. As results, it&rsquo / s observed that, vortex core locations were shifted upwards and away from the tip region. Increasing the turbulence level of the tip flow by tip injection, inherently the pressure difference became larger, however as the vortices ascend, tip loss decreases. In that way, a significant increase in the lift was observed while drag values are slightly increased, as well.

This study investigates the effect of chordwisely modulated tip injection on the flow and turbulence characteristics of the tip vortex through experimental measurements downstream of a rectangular half-wing that has an aspect ratio of three. This injection technique involves spanwise jets at the tip that are issued from a series of holes along the chord line normal to the freestream flow direction. The injection mass flow rate from each hole is individually controlled using computer driven solenoid valves and therefore the flow injection geometrical pattern at the tip can be adjusted to any desired waveform shape, with any proper injection velocity. The measurements are performed in a blow-down wind tunnel using Constant Temperature Anemometry and Kiel probe traverses as well as Stereoscopic Particle Image Velocimetry. Current data show consistent trends with v previously observed effects of steady uniform tip injection such as the upward and outward motion of the vortex as well as increased levels of turbulence within the vortex core. The vortex size gets bigger with injection and the total pressure levels get reduced significantly near the vortex core. The injection pattern also seems to affect the size of the wing wake as well as the wake entrainment characteristics of the tip vortex. Depending on the injection waveform pattern and injection momentum coefficient the helicoidal shape of the tip vortex also seems to get affected.

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L'étude développée dans cette thèse concerne le contrôle des performances et des lâchers tourbillonnaires au cours du cycle de rotation d'une hydrolienne à axe vertical de type Darrieus. L'élaboration d'une famille de lois de commande d'incidence de pales exploitant le principe de conservation de la circulation autour de profils en mouvement permet ici le contrôle du fonctionnement de l'hydrolienne ainsi que la maîtrise de son sillage tourbillonnaire afin de préserver l'environnement.L'écoulement 2D est simulé à l'aide du solveur incompressible de Star CCM+ afin de mettre en évidence l'effet de ce type de contrôle sur le rendement de la turbine pour différents points de fonctionnement. Ce modèle CFD a été utilisé pour améliorer l'analyse analytique en ce qui concerne l'extraction de l'énergie, la compréhension de l'écoulement autour de l'hydrolienne et le contrôle des tourbillons générés. La nouveauté de cette étude est l'élaboration de lois de commande de pales d'hydrolienne, basées sur des valeurs constantes et transitoires de la circulation, afin d'augmenter la puissance de la turbine tout en garantissant un contrôle efficace de la vorticité et ainsi prévenir de l'interaction entre les tourbillons et les pales. Une bonne comparaison est réalisée entre les résultats analytiques et numériques concernant les forces hydrodynamiques.En outre, une campagne d'essais a été menée afin d'acquérir des mesures quantitatives sur une hydrolienne de type Darrieus à pales fixes en terme de puissance, mais aussi des résultats qualitatifs pertinents comme la visualisation de l'écoulement autour des pales à différentes positions et pour différents points de fonctionnement. La mise en place complète d'un système PTV pour les mesures qualitatives et les étapes de traitement sont discutées et les divers paramètres obtenus à partir des études CFD sont validées en utilisant ces résultats PIV.L'étude expérimentale dans la présente recherche appo11e des informations détaillées sur les gradients de pression et de vitesse, les contours de vorticité et le critère Q qui ont servi à valider les visualisations obtenues numériquement. / With key applications in marine renewable energy. the vertical axis water turbine can use current or tidal energy in an eco-friendly manner. However, it is difficult to reconcile optimal performance of hydrokinetic turbines and compliance wilh the aquatic environment as the main drawback of the turbines is the formation of non-linear flow structures caused by the unsteady movement of the blades. Eddies in the flow are advected and can interact with other blades, which leads to a reduction in power output. To limit this phenomenon, the turbines operate at high speeds, which are likely to reduce the shaft power. High speeds of rotational so forbid the passage of aquatic animais, and are the cause of a suction effect on the sediments.The objective of this thesis work is twofold. First, it aims to develop a blade pitch control to get the flow adjusted around the blade profile at any given flow configuration by incorporatin.g the profile's motion with respect to incident flow. Such a system intends to achieve the objective of operating at reduced speeds without vortical releases, which should allow achieving a high torque without causing damage to the environment.This thesis work is mainly carried out in three phases. ln the first phase, the irrotational flow over an arbitrary profile is formulated using conforma] mapping. Prospective potential flow application on the basis of Couchet theory (1976) is involved in the development of a control law that decides the blade pitching in a constant circulation framework. In the second phase, a numerical validation of the developed analytical work is presented using CFD to examine how the theoretical fomulation can be effectively applied to Darricus turbines. In the final phase, two prototypes are developed, one is classical Darrieus turbine with fixed blades, and other is the turbine with pitching blades for experimental measurements of performance as well as flow fields(by PIV) in order to validate the computational results.