An experimental investigation was undertaken to determine the ability of Synthetic Jet Actuators to control the aerodynamic properties of a wing. The Synthetic Jet Actuator (SJA) was placed at two separate positions on a wing comprised of a NACA0015 airfoil. The first of the jet positions is located at 12% of the chord, hereby referred to as the leading edge Synthetic Jet Actuator. The second exit position is located at 99% chord of an airfoil and hereby is referred to as the trailing edge Synthetic Jet Actuator. The two locations produced different benefits as the angle of attack of the wing was increased. The leading edge Synthetic Jet Actuator delayed the onset of stall of an airfoil, suppressing stall up to 25 degrees angle of attack. The control of the aerodynamic characteristics was achieved by influencing the amount of the separated flowfield region. The effects of the dynamic stall vortex were investigated with wind tunnel testing during the pitching motion of an airfoil to determine how the flow reacts dynamically. The trailing edge synthetic jet actuator was investigated as a form of low angle “hingeless” control. The study investigated the effect of the jet momentum coefficient on the ability of the synthetic jet to modify the lifting and pitching moment produced from the wind tunnel model. The data indicates that, with the present implementation, the SJA-jet flap generates moderate lift and moment coefficient increments that should be suitable for hinge- less control. It was also shown that, for the current experimental setup and a given jet momentum coefficient, continuous blowing is more effective than oscillatory blowing/sucking. The data shows that combining the SJA with a Gurney flap does not result in performance enhancement.

A long aspect ratio synthetic jet is produced through an axial slit along part of the length of a cylinder. The jet is excited acoustically by a pair of loudspeakers mounted at the cylinder terminations. The study compares between the performance of two different slits with aspect ratios of 273 and 773. The comparison is based on the spanwise distribution of the mean jet velocity and phase between the jet velocity fluctuations and the excitation signal. Three different frequencies and amplitudes are used to excite the speakers covering the range of frequencies used in the control application. For both cases studied the mean centerline velocity of the jet increases with increasing the amplitude of the exciting signal, but decreases with increasing its frequency. Moreover, velocity deficits of up to 30% are evident as the midspan of the cylinder is approached from either end. Similar trends are also observed for the centerline phase distributions of the velocity fluctuations, with deficits of up to 130°. However, it is observed that for the long slit case the deficits in both the velocity and phase distributions are much larger than those for the short one. The synthetic jet is then mounted in the upstream cylinder of a tandem cylinder arrangement to be used as a control actuator for controlling the vibrations of the downstream cylinder. A simple feedback control mechanism is used at a Reynolds number of about 6.3x104. This Reynolds number corresponds to the case' where the downstream cylinder’s response is dominated with two frequency components, one at the resonance frequency of the cylinder, which is excited by broadband turbulence in the flow, and the other at the vortex shedding frequency. Both slits studied for the characterization experiments are used to compare their performance as control actuators. Both jets produce comparable reductions in the vibration of the downstream cylinder. A reduction of about 20% in the total RMS amplitude of the vibrations signal is achieved. This amounts to a reduction of about 50% in the resonant peak and an average value of about 40% in the vortex shedding peak. The optimal values of gain and time lag of the controller are then used to investigate the effect of the jet on the flow. It is found that the short slit jet produced an effect that was traced up to 1.875 diameters downstream, while the effect of the long slit jet dropped dramatically very close to the upstream cylinder. / Thesis / Master of Applied Science (MASc)

An experimental investigation was undertaken to test the effectiveness of a novel design for controlling the aerodynamics of an airfoil. A synthetic jet actuator (SJA) was placed inside a NACA 0015 airfoil with its jet at 12.5% of the chord length, hereby referred to as the leading edge actuator. Four centrifugal fans across the span were mounted at 70% of the chord and the jet formed by them was located at 99% of the chord, hereby referred to as the trailing edge actuator. The effects of these actuators on the aerodynamic properties were studied, separately and then in conjunction, with varying angles of attack. The leading edge actuator delays the onset of stall up to 24 degrees, the maximum angle of attack that could be attained. The control of the aerodynamics was achieved by controlling the amount of separated region. There was no effect of the actuation at lower angles of attack. The trailing edge actuator provides aerodynamic control at both low and high angles of attack. The study investigated the effect of jet momentum coefficient on the aerodynamic properties for various angles of attack. The data obtained shows that lift control (in both positive and negative direction) was achieved even at low angles. The actuator enhances the aerodynamic properties by changing the pressure distribution as well as by delaying flow separation. Study of the combined actuation shows that the synthetic jet actuator was very effective in delaying stall when the trailing edge jet was ejected from the upper surface. For the case when the jet is ejected from the lower surface, there is less control. This can be accounted for by the difference in aerodynamic loading for both cases.

Like virtually every other human activity, air transport has an impact on the environment and similar to all other industries environmental impacts and economic issues are exerting more pressure on aircraft sector to meet the demands and implicated conditions. Secondly in today’s competitive industrial performance index new modern techniques are being introduced to improve the aerodynamics so that the efficiency of the newly designed aircrafts could be enhanced. The active flow control techniques have been proved vital towards achieving more effective air flow on the aircraft wing and that eventually helps to increase the lift coefficient at full scale flight. Synthetic jet actuators have been experimentally proved a promising technique towards achieving flow separation delay on the surface they have been deployed on. For the operation the synthetic jet actuators offer a unique characteristic in that they make use of the ambient work fluid and that deny the need of any extra fluid from outside the system and that helps in two fold. Firstly the need to make additional arrangements for air supply through the complex piping system has been ruled out completely. Secondly in the system the addition of any new weight that usually associates with the introduction of any new technique has been avoided. In this work firstly the dye visualization technique is used to study the interaction of the synthetic jet with both types of boundary layers that is laminar and turbulent. Secondly PIV measurements are performed to quantitatively analyze the evolution of vortical structures in the boundary layer. The aim is to understand the fluid dynamics involved in the interaction of the vortical structures with the neal wall fluid that ultimately re-attach the flow with the surface. Lastly an artificial flow separation is generated on the deflected flat plate surface and the synthetic jet is deployed to observe the separation delay on the surface. Various vortical structures have been generated by operating the actuator at varying parameters and issued into the boundary layer upstream of the separation line. The effectiveness of each type of vortices has been evaluated quantitatively to work out the optimum parameters at which the actuator must be operated to achieve the best control effect at the given free-stream condition.

Despite many advances in aviation noise control over the past 50 years, the industry is continually striving to reduce noise emissions. Turbofan engine acoustic liners are efficient attenuators of engine noise. Plasma actuators have been used as flow control devices in other settings and will now be studied as an enhancement for acoustic liners. A plasma actuator can excite oscillatory flow or a single direction (bias flow). Both flow types are studied as possible means to excite turbofan liners in order to improve the acoustic performance. Experiments revealed the oscillatory flow as the dominant factor in controlling resonator performance. The phase control of the actuator signal is an important parameter when dealing with the oscillatory flow. The actuator is first applied to a single resonator and then a set of six resonators. The experiments show that with the correct phase, the actuators improved the performance of a single resonator by 3 dB to 5 dB. The results for the array of actuators/resonators mirror the results of a single device. Beyond the improvements in performance, a number of other factors affect the usefulness of the plasma actuator technology in a turbofan environment. The ability of the actuator to produce plasma is susceptible to small imperfections in the device, and this property will likely be amplified in a perforated sheet with embedded actuators. Additional weight and energy consumed by the actuators is another factor to consider. Finally, plasma actuator operation produces ozone, so environmental effects deserve consideration as well. / Master of Science

An experimental investigation was performed to understand the development and suppression of the secondary flow structures within a compact, serpentine jet engine inlet duct. By employing a variety of flow diagnostic techniques, the formation of a pair of counter-rotating vortices was revealed. A modular fluidic actuator system that would apply several different methods of flow control was then designed and manufactured to improve duct performance. At the two bends of the inlet, conformal flow control devices were installed to deliver varying degrees of boundary layer suction, suction and steady fluid injection, and suction and oscillatory injection. Testing showed that suction alone could delay flow separation and improve the pressure recovery of the duct by as much as 70%. However, this technique was not able to rid the duct completely of the nonuniformities that exist at the engine face plane. Suction with steady blowing, however, increased pressure recovery by 37% and reduced distortion by 41% at the engine face. Suction with pulsed injection had the least degree of success in suppressing the secondary flow structures, with improvements in pressure recovery of only 16.5% and a detrimental impact on distortion. The potential for gains in the aerodynamic efficiency of serpentine inlets by active flow control was demonstrated in this study.

Hydro power plants are an essential part of the infrastructure in Sweden as they stand for a large amount of the produced electricity and are used to regulate supply and demand on the electricity grid. Other renewable energy sources, such as wind and solar power, have become more popular as they contribute to a fossil free society. However, wind and solar power are intermittent energy sources causing the demand for regulating power on the grid to increase. Hydro power turbines are designed to operate at a certain design point with a specific flow rate. The plants are operated away from the design point when used to regulate the supply and demand of electricity. This can cause a specific flow phenomenon to arise in the draft tube at part load conditions called a Rotating Vortex Rope (RVR) which causes dangerous pressure fluctuation able to damage blades and bearings. A solution to mitigate a RVR is to inject pulsating momentum into the draft tube by using an actuator operating at a certain frequency. A literature study was conducted and three techniques were numerically simulated using ANSYS Workbench 19.0 R3; a fluidic oscillator, a piston actuator and a synthetic jet actuator. A dynamic mesh was used to simulate the movement of the piston actuator and diaphragm of the synthetic actuator whilst the mesh of the fluidic oscillator was stationary. The relative errors of the three numerical models were all below 3 %. All devices showed promising results and could potentially be used to mitigate a RVR because they all have the ability to produce high energy jets. The fluidic oscillator had an external supply of water, whereas the other two did not, which means that it could inject the largest mass flow. The piston actuator required a driving motor to move the piston. The diaphragm of the synthetic jet actuator was moved by a Piezoelectric element. Advantages of the fluidic oscillator are that it has no moving parts, in contrary to the two other devices, it can directly be connected to the penstock or draft tube to obtain the required water supply and it is easy to install. It will most likely also be smaller compared to the other two for the same mass flow rate. It does however not generate a pulsating jet, but rather an oscillating jet. The other two devices generate pulsating jets, but have problems with low pressure areas during the intake stroke which can cause cavitation problems. These areas cause the formation of vortex rings close to the outlet. Simulations showed that a coned piston together with a coned cylinder outlet could decrease losses by almost 16 % compared to a normal piston and cylinder. It also decreased the risk for cavitation and the required force to move the piston. Otherwise, a shorter stroke length for a constant cylinder diameter or a longer stroke length for a constant volume displacement also decreased the risk for cavitation and required force. The gasket between the piston and cylinder is a potential risk for leakage. A solution to avoid critical low pressure areas is to install an auxiliary fluid inlet or valve which opens at a certain pressure for the piston actuator as well as the synthetic jet actuator. This will also allow larger mass flow rates and a higher injected momentum. Both devices are more complicated to install and require likely more maintenance compared to the fluidic oscillator. However, there exist many possible design options for the piston actuator. The design of the synthetic jet is more limited because of the diaphragm. The amplitude of the diaphragm also has a direct effect on the pressure levels. The losses increased proportional to the mass flow to the power of three which suggests that it is better to install many small actuators instead of a few large ones.

L’amélioration des performances aérodynamiques et environnementales est un enjeu majeur dans le domaine des transports terrestres et aériens. Pour pouvoir répondre à ses exigences, une des solutions est de contrôler les écoulements. Pour cela, des actionneurs performants sont nécessaires. Une technique innovante, le jet synthétique par plasma (JSP), consiste à appliquer une décharge haute tension dans une micro cavité. Un plasma est ainsi créé dans la chambre augmentant en quelques microsecondes la température et la pression du gaz générant un micro-jet par l’orifice de l’actionneur. Le but de la thèse est de développer cet actionneur, d’en comprendre son fonctionnement et de le mettre en oeuvre pour contrôler le bruit d’un jet subsonique à grand nombre de Mach.La première partie de l’étude s’applique à définir les besoins pour le contrôle d’écoulement et de réaliser un prototype d’actionneur. Il est ensuite caractérisé expérimentalement par des mesures de la décharge électrique et de l’aérodynamique du micro-jet. En s’inspirant du modèle de Braginskii, un modèle simple de la décharge électrique est réalisé et appliqué au JSP. Le rendement de l’actionneur en est déduit. Le modèle de Braginskii modifié est ensuite couplé à une modélisation URANS ce qui permet de simuler le fonctionnement en fréquence de l’actionneur. Ces résultats sont ensuite comparés avec les mesures de l’aérodynamique du micro-jet et montrent un excellent accord.L’actionneur est ensuite mis en application pour contrôler le bruit de jet. En premier lieu, des visualisations par strioscopie de l’interaction des micro-jets avec le jet principal sont effectuées. Des mesures acoustiques sont ensuite réalisées etmettent en évidence que les JSP sont de bons candidats pour contrôler le bruit de jet. / Improvement of aerodynamics and environmental performances is a major issue for terrestrial and aeronautical industry.For fulfilling increasing demand, one of the answers is flow control. To achieve flow control, high performance actuators are needed. An innovative technique called Plasma Synthetic Jet actuator consists on applying an electrical discharge in asmall cavity. Plasma is created and increases gas temperature and pressure which results on the creation of a micro-jet through cavity opening.The PhD objectives are to develop the PSJ actuator, to describe actuator mechanisms and to apply it for controlling noise of a high subsonic jet. The first part of the study consists on defining flow control needs and on developing a PSJ actuator prototype. Then,actuator performances are characterised using electrical measurements of the discharge and using aerodynamic measurements. These measurements show that an electrical model of the discharge is needed. Based on the Braginskii model, a simple model is carried out and is applied to the actuator. Efficiency of the PSJ is deduced.The modified Braginskii model is then coupled with an URANS model to achieve frequency modelling of the actuator. Results match aerodynamics measurements .PSJ actuators are applied for controlling jet noise in a second part of the study. Schlieren visualisations are used to show micro-jet interaction with the main jet. Acoustic measurements are then performed and show that the PSJ is a goodactuator to control high subsonic jet noise.

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Die vorliegende Arbeit beschäftigt sich mit der analytischen Modellierung und Optimierung synthetischer Jet-Aktuatoren, welche zur aktiven Strömungsbeeinflussung genutzt werden können. Ein in der Literatur bekanntes eindimensionales Modell wird ausführlich hergeleitet und an gemessene Geschwindigkeitsspektren verschiedener Jet-Aktuatoren angepasst. Der Einfluss jedes Modellparameters wird separat untersucht. Außerdem wird ein empirischer Zusammenhang zwischen Membranresonanzfrequenz und Luftkammervolumen angegeben, mit dessen Hilfe synthetische Jet-Aktuatoren mit größtmöglichen Strömungsgeschwindigkeiten durch die Düse konstruiert werden können.