Vertical axis wind turbine, developed as one of the main methods to utilize the wind energy, has a promising future; however, the major issue to limit its performance is the uneven loading on the blade during operation. Flow control mechanisms have been employed in the aerodynamic field to improve the performance of airfoils. In this study, two types of leading-edge structures, including flexible leading-edge and leading-edge roughness, are experimentally investigated to analyze their effects on altering the aerodynamic characteristics of NACA 0018 airfoil under steady flow condition and dynamic pitching condition. Current experimental results indicate that 1) during the steady flow condition, both of leading-edge structures contribute to the delay of the static stall; 2) for the dynamic pitching process, the leading-edge structures either delayed the dynamic stall angle or increased the area of the coefficient of pressure loop as a function of angle of attack.

The title of my project is living quarters above stables. This idea is based on the long history we have of living together with livestock. I will investigate the possibility of applying this traditional concept in present times and work with the limits and the possibles to integrate modern horse activities in an urban environment. Horse riding is a very popular sport and hobby for Swedish people of all ages. There are more horses than ever living in Sweden today, but they are less visible and integrated  in todays urban planning.  Stockholm is a city which is growing at a very fast pace and the need for a more diversified city has become apparent.   My idea is to offer horse riding enthusiasts who work in the city, the possibility to live in a smaller more practical area within the city, and eliminate the need for them to have to either buy an expensive farm outside the city or travel to stables every day.  This project is about creating a living standard that both the humans and horses can benefit from and bring an increase in satisfaction to their lifestyles. / Titeln på mitt projekt lever kvartal ovanför stallet. Denna idé bygger på den långa historia som vi har att leva tillsammans med boskap. Jag kommer att undersöka möjligheten att tillämpa denna traditionella begreppet i nutid och arbeta med de gränser och de possibles att integrera moderna hästaktiviteter i stadsmiljö. Ridning är en mycket populär sport och hobby för svenskar i alla åldrar. Det finns fler hästar än någonsin i Sverige i dag, men de är mindre synliga och integreras sällan i dagens stadsplanering. Stockholm är en stad som växer i mycket snabb takt och behovet av en mer diversifierad stad har blivit en stor samhälsfråga. Min idé är att erbjuda ridning entusiaster som arbetar i staden, möjlighet att bo i en mindre mer praktiskt område inom staden, och eliminera behovet för dem att behöva antingen köpa en dyr gård utanför staden eller resa till stall varje dag. Projektet handlar om att skapa en levnadsstandard som både människor och djur kan dra nytta av och få en ökad tillfredsställelse till sin livsstil.

In this study, an experimental investigation was performed to characterize the dynamic stall of pitching wings and provide confirmation of the existence of the arch-shaped vortex for moderate sweep wing. Dynamic stall is a complex flow, which happens because of a sudden change of incident angle during the pitching motion. The pitching motion of a wing can cause instability in the shear layer and generate the separation burst at certain angles. For a pitching wing, the dynamic stall vortex is characterized by the formation of an arch-shaped vortex to the evolution of a ring-shaped vortex. The leg of the arch-shaped vortex causes a negative pressure region on the airfoil surface and can, in fact, generate greater lift. However, in certain conditions, the detachment of the arch-shaped vortex from the airfoil surface can cause high pressure and vibration in the structures. The formation of the arch-shaped vortex and its evolution were systematically investigated using cutting-edge flow diagnostic techniques, and the physics of the dynamic stall is explained in addition to providing the confirmation of the theory developed based on Computational Fluid Dynamics. The study was done using Particle Image Velocimetry (PIV) and Pressure-Sensitive Paint for three sweep angle wings. The wings, with an aspect ratio of AR=4 and a NACA 0012 section assembled with round-tip, are considered for the current experimental study. The sweep angles = 0, 15, and 30 degrees were considered to compare the flow phenomena. The PIV results show the formation of a laminar separation bubble and its evolution to a dynamic stall vortex. The increase of sweep angle causes the formation of such vortices towards the wing tip. In the process of finding the footprint of the vortices and pressure distribution on the surface of the wings, a single-shot lifetime method using fast porous paint was used. The results show the existence of suction pressure and later grows towards the trailing edge of the wing due to the formation of a dynamic stall vortex. In addition, at Re=2x10^5 and reduced frequency k=0.2, a moderate sweep airfoil shows the apparent footprint of the arch-shaped vortex, which confirms the current theory.

Neste trabalho apresentamos o desenvolvimento e a realização de um experimento utilizando recursos modernos de processamento de imagens como câmeras CCD, placas de aquisição de imagens e linguagem de programação visual com interface multimídia para observação do fenômeno do Estol dinâmico que tem grande importância do estudo de estabilidade de aeronaves. O fenômeno de Estol ocorre nos aerofólios de aeronaves como nos rotores de helicópteros e asas de aeronaves acrobáticas. Nosso sistema e capaz de detectar dentro de um experimento de um aerofólio oscilando em baixas freqüências a Histerese de sustentação que ocorre neste. Utilizamos também na nossa abordagem redes neurais backpropagation para acomodação dos dados experimentais. Implementamos e descrevemos um hardware mecânico para obtenção de melhores imagens e as funções escritas em Visual Basic que foram utilizadas, com o objetivo de permitir a reprodução do experimento em outros centros de pesquisa. / In this work we present an experiment using modern imaging processing techniques such as CCD cameras, video acquisition boards and visual programming using multimedia interfacing for the observation of the Stall phenomena which has great importance in the airplane stability. The Stall phenomena occurs in arplaine (airfoils) such as in helicopter blades and acrobatic airplane wings. We demonstrated that the developed system is able to detect the lift histeresis in a low frequency oscillating bidimensional airfoil. We also used in our approach backpropagation neural network for the experimental data accomodation. In order to allow replication of the experiment by other institutions, we present a detailed description of the mechanical setup used to obtain the best possible images and of the Visual Basic functions.

Dynamic compressors are susceptible to aerodynamic instabilities while operating at low mass flow rates. These instabilities, rotating stall and surge, are detrimental to engine life and operational safety, and are thus undesirable. In order to prevent stability problems, a passive technique, involving fuel flow scheduling, is currently employed on gas turbines. The passive nature of this technique necessitates conservative stability margins, compromising performance and/or efficiency. In the past, model based active control has been proposed to enable reduction of margin requirements. However, available compressor stability models do not predict the different stall inception patterns, making model based control techniques practically infeasible. This research presents active stability management as a viable alternative. In particular, a limit detection and avoidance approach has been used to maintain the system free of instabilities. Simulations show significant improvements in the dynamic response of a gas turbine engine with this approach. A novel technique has been developed to enable real-time detection of stability limits in axial compressors. It employs a correlation measure to quantify the chaos in the rotor tip region. Analysis of data from four axial compressors shows that the value of the correlation measure decreases as compressor loading is increased. Moreover, sharp drops in this measure have been found to be relevant for stability limit detection. The significance of these drops can be captured by tracking events generated by the downward crossing of a selected threshold level. It has been observed that the average number of events increases as the stability limit is approached in all the compressors studied. These events appear to be randomly distributed in time. A stochastic model for the time between consecutive events has been developed and incorporated in an engine simulation. The simulation has been used to highlight the importance of the threshold level tosuccessful stability management. The compressor stability management concepts have also been experimentally demonstrated on a laboratory axial compressor rig. The fundamental nature of correlation measure has opened avenues for its application besides limit detection. The applications presented include stage load matching in a multi-stage compressor and monitoring the aerodynamic health of rotor blades.

In this investigation, casing mounted high frequency response pressure transducers are used to characterize the flow behavior near the aerodynamic stability limit of a low speed single stage axial flow compressor. Time variant pressure measurements are acquired at discrete operating points up to the stall inception point and during the transition to rotating stall, for a length of time no shorter than 900 rotor revolutions. The experimental data is analyzed using multiple techniques in the time and frequency domains. Experimental results have shown an increase in the breakdown of flow periodicity as the flow coefficient is reduced. Below a flow coefficient of 0.40 a two node rotating disturbance develops with a propagation velocity of approximately 23% rotor speed in the direction of rotation. During rotating stall, a single stall cell is present with a propagation velocity of approximately 35% rotor speed. The stall inception events present are indicative of a modal stall inception.

Neste trabalho apresentamos o desenvolvimento e a realização de um experimento utilizando recursos modernos de processamento de imagens como câmeras CCD, placas de aquisição de imagens e linguagem de programação visual com interface multimídia para observação do fenômeno do Estol dinâmico que tem grande importância do estudo de estabilidade de aeronaves. O fenômeno de Estol ocorre nos aerofólios de aeronaves como nos rotores de helicópteros e asas de aeronaves acrobáticas. Nosso sistema e capaz de detectar dentro de um experimento de um aerofólio oscilando em baixas freqüências a Histerese de sustentação que ocorre neste. Utilizamos também na nossa abordagem redes neurais backpropagation para acomodação dos dados experimentais. Implementamos e descrevemos um hardware mecânico para obtenção de melhores imagens e as funções escritas em Visual Basic que foram utilizadas, com o objetivo de permitir a reprodução do experimento em outros centros de pesquisa. / In this work we present an experiment using modern imaging processing techniques such as CCD cameras, video acquisition boards and visual programming using multimedia interfacing for the observation of the Stall phenomena which has great importance in the airplane stability. The Stall phenomena occurs in arplaine (airfoils) such as in helicopter blades and acrobatic airplane wings. We demonstrated that the developed system is able to detect the lift histeresis in a low frequency oscillating bidimensional airfoil. We also used in our approach backpropagation neural network for the experimental data accomodation. In order to allow replication of the experiment by other institutions, we present a detailed description of the mechanical setup used to obtain the best possible images and of the Visual Basic functions.

Accurately predicting fan performance, including bounds of operation, is an important function of any Computational Fluid Dynamics (CFD) package. The presented research uses a CFD code developed as part of the Computational Research and Engineering Acquisition Tools and Environment (CREATE), known as Kestrel, to evaluate a single stage compressor at various operating conditions. Steady-state, single-passage simulations are carried out to validate capabilities recently added to Kestrel. The analysis includes generating speedlines of total pressure ratio and efficiency, as well as radial total temperature and total pressure profiles at two axial locations in the compressor at various operating conditions and fan speeds, and simulation data from the single-passage runs is compared to experimental data. Time-accurate, full annulus simulations are also carried out to capture and analyze the processes leading to stall inception for both uniform and distorted inlet conditions. The distortion profile used contains a 90 degree sector of lower total pressure at the inlet. The observed fan behavior at stall inception is compared to previous research, and it is concluded that the inlet distortion significantly changes the behavior of the part-span stall cells that develop after stall inception. Understanding the physical processes that lead to stall inception allows fan designers to design more robust fans that can safely take advantage of the better performance associated with operating closer to stall.

The quest to accurately capture flow phenomena with length-scales both short and long and to accurately represent complex flow phenomena within disparately sized geometry inspires a need for an efficient, highidelity, multi-block structured computational fluid dynamics (CFD) parallel computational scheme. This research presents and demonstrates a more efficient computational method by which to perform multi-block structured CFD parallel computational simulations, thus facilitating higheridelity solutions of complicated geometries (due to the inclusion of grids for "small" flow areas which are often merely modeled) and their associated flows. This computational framework offers greater flexibility and user-control in allocating the resource balance between process count and wallclock computation time. The principal modifications implemented in this revision consist of a "multiple grid-block per processing core" software infrastructure and an analytic computation of viscous flux Jacobians. The development of this scheme is largely motivated by the desire to simulate axial compressor stall inception with more complete gridding of the flow passages (including rotor tip clearance regions) than has been previously done while maintaining high computational efficiency (i.e., minimal consumption of computational resources), and thus this paradigm shall be demonstrated with an examination of instability in a transonic axial compressor. However, the paradigm presented herein facilitates CFD simulation of myriad previously impractical geometries and flows and is not limited to detailed analyses of axial compressor flows. While the simulations presented herein were technically possible under the previous structure of the subject software, they were much less computationally efficient and thus not pragmatically feasible; the previous research using this software to perform three-dimensional, full-annulus, timeurate, unsteady, full-stage (with sliding-interface) simulations of rotating stall inception in axial compressors utilized tip clearance periodic models, while the scheme here is demonstrated by a simulation of axial compressor stall inception utilizing gridded rotor tip clearance regions. As will be discussed, much previous research --- experimental, theoretical, and computational --- has suggested that understanding clearance flow behavior is critical to understanding stall inception, and previous computational research efforts which have used tip clearance models have begged the question, "What about the clearance flows?". This research begins to address that question.

Core engine icing has been recognized to affect a wide variety of engines since the 1990's. This previously unrecognized form of icing occurs in flights through high altitude convective regions and vicinity of thunderstorms. Engine icing events involve power loss or damage associated to the engine core, namely instabilities such as compressor surge, stall, engine rollback and even combustor flameout events. The effects on compressor performance are significant in understanding the response of the engine to atmospheric ice ingestion. A one-dimensional axisymmetric flow model is used to simulate the continuous phase through the compressor. The steady state operation of dry air is validated with an industrial database. By changing an exit throttle, the point where the dry compressor mass flow rate slowly starts to drop, is predicted. The stage that is the first to locally collapse, causing the remaining stages and eventually the complete compressor failure, is determined. The continuous flow model is then coupled with a Lagrangian model for the discrete phase in a framework that conserves mass, momentum and energy. From numerical simulations of the coupled, continuous-discrete phase flow model, it is observed that a rematching of the stages across the compressor occurs with increasing ice flow rates to accommodate loss of energy to the ice flow. The migration of the operating point towards the stall point at the rear stage eventually causes the compressor to stall. The onset of stall is characterized by initial oscillations followed by a rapid decay of pressures of the last stage with the instability traveling quickly towards the front of the compressor. Effectively, a reduction in the compressor stall margin is observed as the ice flow rate increases. Further, the relevance of factors such as blockage due to discrete particles and break/splash semi-empirical models in the icing physics, are analyzed through parametric studies. Conclusions are drawn that underscore the influence of the assumptions and models in prediction of the flow behavior in the presence of ice ingestion. Smaller ice crystal diameters have a greater influence on the gas flow dynamics in terms of a higher reduction in surge margin. The break empirical model for ice crystals and splash model for the droplets that are used to calculate the secondary particle size upon impact with rotor blades have a significant influence on the gas flow predictions.