Tesi sul tema "PROFILE VORTEX"

An isolated wing-tip vortex from a square-tipped NACA 0012 wing at an angle of attack of 5 degrees was studied in a water tunnel at a chord based Reynolds number of approximately 24000. Measurements were taken using stereo particle image velocimetry at three measurement planes downstream of the wing under each of three freestream turbulence conditions. The amplitude of wandering of the vortex axis increased with increasing distance downstream of the wing and with increasing freestream turbulence intensity. The magnitude of the peak azimuthal velocity decreased with increasing distance from the wing as well as with increases in the freestream turbulence intensity. The streamwise velocity in the vortex core was less than the freestream velocity in all cases. Time resolved histories of the instantaneous waveform shape and location of the vortex axis were determined from sequences of images of fluorescent dye released from the wing.

Objetivo: Analisar in vitro a capacidade de corte e a resistência à fadiga cíclica dos sistemas rotatórios ProFile Vortex (Dentsply Tulsa Dental, USA) e ProTaper (Dentsply Maillefer, Suíça). Metodologia: Para a análise da capacidade de corte, pesou-se em balança analítica digital cem blocos de resina fenólica que continham canais simulados com 75 de curvatura, obtendo-se os pesos iniciais (P0) e após a instrumentação dos canais, estes blocos foram novamente pesados obtendo-se os pesos finais (P1). Dividiram-se quarenta instrumentos em dois grupos. Grupo A: vinte instrumentos ProFile Vortex n25; 25mm; taper.06 e Grupo B: vinte instrumentos ProTaper F1; 25mm. Subdividiu-se em dois subgrupos com dez amostras cada, de acordo com o número de usos, sendo estabelecidos da seguinte maneira: grupos A0 e B0, instrumentos sem nenhum uso e grupos A5 e B5, instrumentos de cinco usos. Avaliou-se a resistência à fadiga cíclica submetendo-se todos os instrumentos a ensaio dinâmico, utilizando-se dispositivo desenvolvido para tal, até a ocorrência da fratura que foi constatada visualmente. O número de ciclos até a fratura assim como o tempo expresso em segundos foram registrados e realizou-se estatística descritiva, o teste `t de Student e o teste de Mann-Whitney. Resultados: Em todos os blocos houve perda de peso, porém sem significado estatístico (Pvalor>0,05). Os instrumentos Profile Vortex removeram mais material e completaram maior número de ciclos até a fratura, com significância estatística (Pvalor>0,05) quando comparados com os instrumentos Protaper. Conclusão: A capacidade de corte em função do número de uso e a resistência à fadiga cíclica, nos parâmetros utilizados neste estudo, foram maiores para os instrumentos Profile Vortex quando comparados com os instrumentos Protaper.
Aim: The aim of this study was to evaluate in vitro the ability to cut and cyclic fatigue resistance of rotary systems ProFile Vortex (Dentsply Tulsa Dental, USA) and ProTaper (Dentsply Maillefer, Switzerland). Methods: To analyze the ability to cut weight in analytical scale digital block one hundred made of phenolic resin containing simulated channels 75 curvature obtaining to the initial weights (P0) and following the instrumentation of canals, these blocks were weighed again obtaining is the end weight (P1). Instruments forty were divided into two groups. Group A: twenty ProFile Vortex instruments n25, 25mm; taper.06 and Group B: twenty ProTaper instruments F1, 25mm. Subdivided into two subgroups with ten samples each, according to the number of uses, is established as follows: A0, B0 groups, without using tools and groups A5 and B5, five uses instruments. To evaluate the fatigue resistance cyclic submitting all the dynamic test instruments using device developed for this purpose, until the occurrence of fracture was observed visually. O number of cycles fracture to and the time in seconds were recorded and analysis descriptive, the `t Student test and Mann-Whitney. Results: In every block there was weight loss, however no statistical significance (Pvalor> 0.05). The Vortex Profile instruments removed more material and completed a greater number of cycles to fracture, with statistical significance when compared with the instruments Protaper (Pvalor> 0.05). Conclusions: The cutting ability the number of use and cyclic fatigue resistance, the parameters used in this study were higher for the Vortex Profile instruments when compared with Protaper instruments.

The mechanical properties of endodontic instruments are important parameters for the safe and efficient clinical use in endodontic practice. The aim of this study was to evaluate the geometric characteristics, the structural, physical, chemical and mechanical properties of NiTi endodontic instruments ProFile Vortex, RaCe and ProTaper Universal. The chemical components have all been analyzed with X-Ray energy spectroscopy, the present phases determined by X-Ray diffractions, the transformation temperatures obtained with differential scanning calorimeter and the topographic features were evaluated by scanning electron microscopy. The geometric and dimensional characteristics, especially the area and diameter 3 mm from the tip were analyzed using the ImagePro Plus 6.0 software. The mechanical behavior was evaluated by bending and torsion tests, as specified by ISO 3630-1, and flexural fatigue test until fracture. Data were analyzed by ANOVA with a confidence level of 95%. The instruments Vortex, RaCe and ProTaper Universal showed similar chemical composition and -phase as the main constituent at room temperature. However, the average values of transformation temperatures of the instrument Vortex were significantly higher than other rotary systems tested. The Vortex instruments were significantly more flexible, possibly due to thermomechanical treatments they have undergone during manufacture. Instruments Vortex 25/.06 showed peak torque significantly higher than those of RaCe 25/.06 and ProTaper F1. However, in the group with the highest caliber, ProTaper F2 instrument showed the statistically most torsional resistance. In the fatigue tests, Vortex system showed a significantly higher fatigue life than the other instruments examined. Whereas instruments have similar diameters and geometry, the thermomechanical treatment performed in the M-Wire wire used in producing the Vortex system, represented an important improvement in the mechanical properties of the instruments, when compared with rotary systems manufactured with conventional NiTi wires.
As propriedades mecânicas dos instrumentos endodônticos são parâmetros relevantes para o uso clínico seguro e eficiente na prática endodôntica. O objetivo deste trabalho foi avaliar as características geométricas, as propriedades estruturais, físicas, químicas e mecânicas dos instrumentos endodônticos de NiTi ProFile Vortex, RaCe e ProTaper Universal. A composição química da liga NiTi foi analisada semi-quantitativamente por espectroscopia de energia de raios-X, as fases presentes foram identificadas através de análises por difratometria de raios-X, as temperaturas de transformação foram determinadas por calorimetria exploratória diferencial e o acabamento superficial foi avaliado por microscopia eletrônica de varredura. As características geométricas e dimensionais, principalmente diâmetro e a área a 3 mm da ponta foram analisadas através do software ImagePro Plus 6.0. O comportamento mecânico foi avaliado através de ensaios de flexão e torção, conforme especificação ISO 3630-1, e teste de fadiga flexural até fratura. Os dados foram analisados pelo teste ANOVA com um nível de confiança de 95%. Os instrumentos Vortex, RaCe e ProTaper Universal apresentaram composição química semelhante e fase como principal constituinte à temperatura ambiente. Entretanto, os valores médios das temperaturas de transformação do instrumento Vortex foram estatisticamente maiores do que os demais sistemas rotatórios testados. Os instrumentos Vortex foram significativamente mais flexíveis, possivelmente devido aos tratamentos termomecânico a que foram submetidos durante a fabricação. Os instrumentos Vortex 25/.06 apresentaram valores de torque máximo significativamente superiores àqueles dos instrumentos RaCe 25/.06 e ProTaper F1. Porém, no grupo com maior calibre, o instrumento ProTaper F2 foi o que apresentou estatisticamente a maior resistência torcional. Nos ensaios de fadiga, sistema Vortex apresentou uma vida em fadiga significativamente maior que os demais instrumentos analisados. Considerando que os instrumentos apresentam geometria e diâmetros similares, o tratamento termomecânico realizado no fio M-Wire utilizado na produção do sistema Vortex, representou importante melhora nas propriedades mecânicas dos instrumentos, quando comparado com sistemas rotatórios fabricados com fios de NiTi convencionais.

The purpose of this study was to determine the number of rotations to fracture (cyclic fatigue) of the Profile® Vortex™ files (Dentsply Tulsa Dental Specialties, Tulsa, OK) compared to the EndoSequence™ files (Brasseler USA, Savannah, GA) using an in-vitro apparatus simulating a curved canal. Two hundred Profile® Vortex™ files of 25mm length were divided equally into ten groups, one for each of the Profile® Vortex™ files 20/0.04, 20/0.06, 25/0.04, 25/0.06, 30/0.04, 30/0.06, 35/0.04, 35/0.06, 40/0.04, and 40/0.06. Two hundred EndoSequence™ files of 25mm length were divided equally into ten groups of the same tip and taper sizes analogous to the Profile® Vortex™ file groups. Files were rotated at 500 rpm in a fixed groove in the metal block of the apparatus. The angle of deflection for all files was fixed at 33 degrees, determined using the Schneider method. The time from initiation of rotation to fracture was recorded and rotations to fracture were calculated. The data collected was analyzed using a multi-way ANOVA, followed by specific post-hoc contrasts comparing the two brands for each tip and taper combination. The results demonstrated that the Profile® Vortex™ files required significantly greater rotations to fracture than the EndoSequence™ (p < 0.001) in all tip sizes in both 0.04 and 0.06 tapers. Profile® Vortex™ files exhibited a greater resistance to cyclic fatigue than the EndoSequence™ files.

The main aim of this thesis was to understand the mechanism behind the classical transition scenario inside the boundary layer over an airfoil and eventually attempting to control this transition utilizing passive devices for transition delay. The initial objective of analyzing the transition phenomenon based on TS wave disturbance growth was conducted at 90 Hz using LDV and CTA measurement techniques at two different angles of attack. This was combined with the studies performed on two other frequencies of 100 and 110 Hz, in order to witness its impact on the neutral stability curve behavior. The challenges faced in the next phase of the thesis while trying to control the transition location, was to understand and encompass the effect of adverse pressure gradient before setting up the passive control devices, which in this case was miniature vortex generators. Consequently, several attempts were made to optimize the parameters of the miniature vortex generators depending upon the streak strength and stability. Finally, for 90 Hz a configuration of miniature vortex generators have been found to successfully stabilize the TS wave disturbances below a certain forcing amplitude, which also led to transition delay.

AQUESTA TESI DOCTORAL ES CONFIGURA COM UN COMPENDI DE TRES ARTICLES I ES BASA EN L'AVALUACIÓ DE LA DEFORMACIÓ QUE ES PRODUEIX A NIVELL DEL FORAMEN MAJOR QUAN UTILITZEM ELS INSTRUMENTS ENDODÒNTICS MÉS ENLLÀ DE LA LONGITUT DE TREBALL, QUAN SOBREPASSEN EL FORAMEN MAJOR, JA SIGUI EN REALITZAR LA PERMEABILITAT APICAL O COM A CAUSA D'UNA SOBRE-INSTRUMENTACIÓ MECÀNICA. LES TREBALLS VAN CONCLOURE QUE LES LLIMES K-FLEX # 08 NO PRODUEIXEN DEFORMACIÓ APICAL EN LA MAJOR PART DELS CASOS. A MÉS, LES LLIMES K # 10 I C-PILOT # 10 PODEN SER UTILITZADES DE FORMA SEGURA PER A DUR A TERME LA PERMEABILITAT JA QUE LA DEFORMACIÓ PRODUÏDA PER AMBDUES ÉS MÍNIMA. NO OBSTANT, TOTES LES LLIMES ROTATÒRIES DE NÍQUEL-TITANI ANALITZADES VAN PRODUIR DEFORMACIÓ APICAL.
ESTA TESIS DOCTORAL SE CONFIGURA COMO UN COMPENDIO DE TRES ARTÍCULOS Y SE BASA EN LA EVALUACIÓN DE LA DEFORMACIÓN QUE SE PRODUCE A NIVEL DEL FORAMEN MAYOR CUANDO UTILIZAMOS LOS INSTRUMENTOS ENDODÓNTICOS MAS ALLÁ DE LA LONGITUD DE TRABAJO, CUANDO SOBREPASAN EL FORAMEN MAYOR, YA SEA AL REALIZAR LA PERMEABILIDAD APICAL O COMO CAUSA DE UNA SOBRE-INSTRUMENTACIÓN MECÁNICA. LOS HALLAZGOS CONCLUYERON QUE LAS LIMA K-FLEX#08 NO PRODUCE DEFORMACIÓN APICAL EN LA MAYORÍA DE LOS CASOS. ADEMÁS LAS LIMAS K#10 Y C-PILOT#10 PUEDEN SER UTILIZADAS DE FORMA SEGURA PARA REALIZAR LA PERMEABILIDAD YA QUE LA DEFORMACIÓN PRODUCIDA POR AMBAS EN MÍNIMA. SIN EMBARGO TODAS LAS LIMAS ROTATORIAS DE NIQUEL-TITANIO ANALIZADAS PRODUJERON DEFORMACIÓN APICAL

The doctoral thesis deals with the analysis of the flow in the circular and not circular cross-section pipes by methods using the distribution of the vorticity density. This analysis is particularly focused on the derivation of the new velocity profiles formulas using the above mentioned method. In this work is presented a historical overview of the derived velocity profiles. This overview of already derived velocity profiles will be a fundamental benchmark for newly derived velocity profiles. These new velocity profiles are derived for the circular and not circular cross-section pipes and the derivation is based on the analogy of electromagnetic induction by using Biot-Savart law. It is necessary to apply this analogy at first on solitary vortex filament. By taking this step is possible to get the value of the induced velocity from one solitary vortex filament. Subsequently it is possible to obtain the value of the induced velocity from the vorticity wall and afterwards from the vorticity density distribution over the cross section. This work contains also the results of the experimental measurements of the velocity profiles, and of the CFD simulations. Experimentally measured results are used besides other for the selecting of the most suitable CFD computational model. Selected CFD model will be subsequently declared as a reference model and the valid velocity profiles for this model will serve with the experimentally measured data as a benchmark for the newly derived velocity profiles.

The operating range and efficiency of a centrifugal compressor is limited by the development of rotating stall and surge at low mass flow rates. To extend the operating range of a compressor, flow control in the compressor can be used to suppress secondary flow structures that lead to rotating stall. The presented work seeks to use the novel idea of placing passive vortex generators (VG) upstream of the impeller to suppress rotating stall, while also developing new concepts and optimization of microvortex generators (MVG). To accomplish this goal, a new SIMPLE-type algorithm for compressible flows was written in Code_Saturne along with a 2nd-order MUSCL scheme for convective terms and an AUSM+-up scheme for mass flux computation. The new algorithm was successfully validated against several widely-used test cases. The new algorithm was used to model the flow of the NASA CC3, a high-speed centrifugal compressor, from choke to rotating stall with a vaneless and vaned diffuser. The new algorithm predicted the performance of the compressor with a vaneless diffuser very well; satisfactory results were obtained for the compressor with a vaned diffuser. The full compressor with a vaned diffuser was used to model rotating stall. A complex stall cycle between the inlet of the impeller and diffuser was observed and studied. The fundament behavior of MVG, i.e. micro (sub-boundary layer) vortex generator, in a turbulent boundary layer was investigated in a channel flow with RANS and LES. Complementary wind tunnel testing was conducted to validate the computational predictions. The configuration of the MVG was studied to determine an optimal configuration and several conclusions were reached on the design of MVG. Most importantly triangle MVG were found to be the most efficient shape followed by NACA0012 and e423-type MVG, and a MVG angle of 18˚ to 20˚ was found to be optimal. Rectangle MVG were observed to suffer flow separation on the vanes which reduced their performance. The circulation and drag of a MVG was found to have a logarithmic relationship with the device's Reynolds number. These findings were incorporated in a LES study to control separated flow on the e387 airfoil and achieved an improvement in lift-to-drag ratio of 11.27%. Additional recommendations for MVG implementation were given. Combining the work on the NASA CC3 with the work on MVG, vortex generators were implemented near the inlet of the impeller. A detailed optimization study was conducted for the implementation vortex generators in the compressor. It was found vortex generators equal to the boundary layer thickness were the most efficient on controlling the downstream flow. The best configuration was implemented into the full compressor with a vaned diffuser to assess the ability of vortex generators to suppress rotating stall. The vortex generators were found to suppress rotating stall and extend the operating range of the compressor.

This master's thesis deals with simulation of vortex structure which is created in the draft tube of Francis turbine, at part load flow conditions. The main objective is to get the most accurate results from the calculations, using the student license of Ansys Fluent 19.1. The results from the calculations are compared with the experiment under the Francis-99 project. Mainlly in terms of dynamic properties of vortex rope – aplitude and frequency of pressure pulsations. Additionaly the time-averaged velocity profiles are compared. I used the test-case provided by NTNU – Norwegian University of Science and Technology under the Francis-99 workshop series.

En soufflerie subsonique, on genere un tourbillon a partir du decrochage dynamique d'un volet mis rapidement en incidence par commande numerique. Ce tourbillon unique et reproductible se detache et est convecte par l'ecoulement sur un profil naca0012. Cette maquette, montee sur une balance de portance et de trainee instationnaires est munie de prises de pression multiplexees sur un capteur par un commutateur pneumatique

Certains profils verticaux d'ozone montrent des fluctuations de petite echelle qui se manifestent par des maxima et des minima relatifs autour du profil vertical moyen. Dobson (1973) est le premier auteur qui a mis l'accent sur l'existence de ces fluctuations. Elles sont attribuees a l'advection des masses d'air de differentes origines a une meme colonne verticale d'air. Cependant le mecanisme responsable de cette advection n'est pas tres bien connu. Cette these se propose de montrer qu'il existe deux mecanismes differents qui constituent des causes importantes dans la generation des fluctuations du profil vertical d'ozone. Le premier mecanisme est le deplacement des parcelles d'air sous l'effet d'une onde de gravite et le deuxieme mecanisme est l'advection isentrope de masses d'air. Pour le role des ondes de gravite, on est amene a revoir quelques elements de theorie lineaire des ondes de gravite. Ceci nous permet d'obtenir la relation de dispersion et surtout les relations de phases entre les fluctuations de differents parametres atmospheriques en presence d'une onde de gravite. Ensuite, on etudie le lien theorique entre les fluctuations normalisees du rapport de melange d'ozone et celles de la temperature potentielle, et sa dependance de la periode intrinseque de l'onde et des gradients horizontal et vertical. On confirme ce lien par l'analyse de donnees obtenues pendant la campagne easoe, qui comportent des mesures simultanees d'altitude, de pression, de temperature, de pression partielle d'ozone et dans certains cas du vent horizontal (grandeur et direction). Pour le role des advections isentropes, on etudie les fluctuations induites par le transport de masses d'air sur des surfaces isentropes, dans leurs relations avec les structures filamentaires du vortex polaire. Dans cette etude, on confirme dans un premier temps que la technique d'advection-chirurgie des contours (cas) represente mieux la structure reelle du vortex que celle qu'on tire directement a partir des analyses. On montre ensuite que l'extrusion isentrope d'air du vortex vers la zone qui l'entoure, et l'intrusion d'air venant de basses latitudes peuvent produire des fluctuations dans le profil vertical d'ozone

To predict fluid properties and interactions is an important task for the industry. It is plagued, however, by being close to impossible to predict analytically. Hence, it is customary to turn to numerical solutions. This in itself comes with many different methods and approaches suitable for different needs. This work focuses on two methods: Tip Vortex Index (TVI) and Diffused Vortex Hydrodynamics (DVH). TVI is a method to predict when a marine propeller will experience cavitation of tip vortices and is based on calculations from a Boundary Element Method (BEM). DVH is a particle method for simulating the circulation of a fluid in two dimensions and three dimensions. The aim is to investigate an implemented TVI model based on MPUF-3A for different marine propeller series, with different sub-designs for a total of 28 unique propellers, and implement the DVH method and test it for 3 different bodies. The results of this thesis show that the implemented TVI model is non-functional for the 28 different propellers, but the DVH method is successfully implemented and able to handle 2 different bodies.
Att förutspå fluid egenskaper och interaktioner är en viktig uppgift för industrin. Det plågas dock av att vara näst intil omöjligt att förutspå analytiskt. Det är därför vanligt att vända sig till numeriska lösningar. Detta kommer i sig med många olika metoder och tillvägagångssätt som passar olika behov. Detta arbete fokuserar på två metoder: Tip Vortex Index (TVI) och Diffused Vortex Hydrodynamics (DVH). TVI är en metod för att förutsäga när en marin propeller kommer att uppleva kavitation av spetsvirvlar och baseras på beräkningar från en Boundary Element Method (BEM). DVH är en partikelmetod för att simulera cirkulationen i fluid i två dimensioner och tre dimensioner. Syftet är att undersöka en implementerad TVI-modell baserad på MPUF-3A för olika marina propellerserier, med olika underdesigner, för totalt 28 unika propellrar, och implementera DVH-metoden och testa den för 3 olika kroppar. Resultaten av denna avhandling visar att den implementerade TVI-modellen är icke-funktionell för de 28 olika propellrarna, men DVH-metoden är framgångsrikt implementerad och kan hantera 2 olika kroppar

L'enveloppe de vol des hélicoptères est limitée par le décrochage dynamique, que le contrôle d'écoulement permet de surmonter. Malgré de nombreuses études, aucun dispositif de contrôle ne s'est révélé utilisable sur un rotor. Conçu par l'ONERA, un Vortex Generator déployable (DVG) s'est révélé efficace pour limiter les effets du décrochage dynamique d'un profil OA209 en oscillation de tangage. Mais l'étude de cet actionneur est nécessaire avant son application. Le travail exposé dans le présent mémoire s'attache à reproduire par simulations numériques l'écoulement du décrochage dynamique contrôlé par DVG afin d'identifier les phénomènes physiques en jeu. Après une première partie bibliographique dédiée au contrôle de décrochage dynamique et aux Vortex Generators, une seconde partie a été consacrée à valider et étudier la simulation numérique du contrôle du décrochage statique. L'écoulement induit a pu être ainsi caractérisé par les interactions tourbillonnaires présentes du fait de l'épaisseur du DVG et qui réduisent l'efficacité du contrôle. Cette analyse a permis d'élaborer une modélisation préliminaire du DVG. Dans une troisième partie, la validation et l'étude de la simulation numérique du contrôle du décrochage dynamique a mis en évidence un effet de contrôle similaire au cas statique, et la décomposition en modes propres orthogonaux de l'écoulement contrôlé a montré une altération du mode lié au tourbillon de décrochage dynamique. Ce travail valide la simulation numérique mise en place, laisse entrevoir des perspectives d'amélioration du dispositif de contrôle et permet la simulation numérique ultérieure du contrôle de décrochage dynamique de voilure tournante
The helicopter flight envelope is limited by dynamic stall, which can be reduced by flow control actuation. Numerous studies are dedicated to the alleviation of dynamic stall, however no actuator has ever been used on real rotor configuration. A new deployable Vortex Generator-type actuator called DVG has been designed by the ONERA and proved its efficiency over pitch-oscillating dynamic stall control of an OA209 airfoil. However, the control effect must be in-depth analyzed before further application. Therefore, the present works aims at reproducing the dynamic stall control through numerical simulations,in order to investigate the physics involved. After a first part dedicated to the literature review of dynamic stall control and Vortex Generators, a second part considered the validation and investigation of the static stall control. DVG-induced secondary flow has been characterized by its vortex interactions, which reduce the control efficiency because of the DVG thickness. This analysis made a preliminary modeling of the DVG possible. In a third part, validation and investigation of the dynamic stall control have been performed, and the actuation showed strong similarities with the static case. Eventually, Proper Orthogonal Decomposition of the flow brought evidence of Dynamic Stall Vortex mode distortion thanks to DVG presence. This work validates the numerical simulation methodology, lets hope possible improvement of the actuator design and allows further numerical simulations of dynamic stall control over real helicopter blades

Le décrochage profond est un cas particulier du décrochage d’un avion, où l'empennage horizontal est entièrement situé dans le sillage décollé de la voilure principale. Le plan perd ainsi son efficacité, ce qui se traduit par une position d'équilibre en tangage stable, à une incidence élevée, dont il est impossible de sortir par une manœuvre simple. L’objectif de cette étude est de caractériser l’aérodynamique associée à ce phénomène et de proposer une procédure d’identification et de récupération. Il est proposé une démarche visant à déterminer la dynamique bidimensionnelle de l’écoulement autour d’une configuration aéronautique de référence. Les coefficients aérodynamiques, obtenus dans une large plage d’incidence, mettent en évidence l’effet de l’interaction entre les profils sur le décrochage, qui impacte principalement le profil aval. L’analyse des champs de vitesse fournit l’étendue et l’évolution axiale des sillages des profils. Un traitement des champs de vitesse par moyennes de phase permet de reconstruire la dynamique temporelle. À partir de ces résultats, un modèle potentiel de forçage de l’écoulement autour du profil aval permet d’expliquer la modification du coefficient de portance imposé par l’interaction. Des simulations numériques de l’écoulement, qui fournissent des champs résolus en temps, permettent de retrouver certaines évolutions expérimentales. L’ensemble des résultats est utilisé, en parallèle à des données issues d’un aéronef réel, dans un modèle de vol longitudinal afin d’analyser le comportement dynamique de l’avion. Des critères permettant d’identifier la dynamique qui conduit à cet équilibre, fournissent une détection précoce de ce dernier
Deep stall is a specific type of airplane stall, in which the horizontal tail is inside the detached wake of the main wing. The tail loses its efficiency, leading to a stable pitching equilibrium position with a high angle-of-attack, without any easy recovery procedure. The aim of the study is to characterize the aerodynamic associated to that phenomenon in order to propose an identification and recovery procedure. The approach consists in a two-dimensional flow characterization based on an aeronautical reference configuration. Aerodynamic coefficients, obtained for a wide range of angles-of-attack, show the interaction between the airfoils on the stall of the downstream airfoil. The analysis of velocity fields gives the width and the axial development of the airfoils wakes. Phase-averages of velocity fields lead to the synthesis of flow time-development. With these results, a potential model of flow forcing on the downstream airfoil explains the lift coefficient alteration imposed by the interaction. Flow numerical simulations, giving time-resolved fields, provide good accordance with experimental developments .The whole set of results is used, concurrently with real aircraft data, inside a longitudinal flight model in order to analyze the airplane dynamical behavior. Criteria for the identification of the dynamic leading to that equilibrium provide a rapid detection of deep stall and the implementation of a recovery strategy

Liquid and gas do not separate naturally in microgravity, presenting a problem for twophase space systems. Increased integration of multiphase systems requires a separation method adaptable to a variety of systems. Researchers at Texas A&M University (TAMU) have developed a microgravity vortex separator (MVS) capable of handling both a wide range of inlet conditions and changes in these conditions. To optimize the MVS design, the effects of nozzle area, separator geometry, and inlet flow rate must be understood. Computational fluid dynamics (CFD), in the form of Adapco’s Star-CD, is used, along with laboratory testing, to accomplish this goal. Furthermore, as analysis aids for the laboratory data and CFD results, relationships for radial pressure, bubble transit time, and momentum transfer were developed. Ground testing data showed a linear relationship between rotational speed and inlet flow rate. The CFD results compared well with the ground data and indicated that the majority of the rotational flow travels at nearly the same rotational speed. Examination of the tangential velocity profile also showed that a reduction of nozzle outlet area resulted in increased tangential velocities. Using dimensional analysis, a relationship between separator radius, inlet momentum rate, fluid properties, and rotational speed was found. Applying this relationship to the ground data and CFD results showed a strong correlation between the two dimensionless groups. Linear regression provided an equation linking rotational speed to the separator parameters. This equation was tested against the ground data and shown to predict average rotational speed well for all separator models. These results were used to calculate the radial and axial transit times of gas bubbles within the separation volume. Radial transit time was found to decrease more rapidly than axial transit time as gas volume increased, indicating axial and radial transit times are closest in value for the all liquid case and increasing gas core diameter improves the operational characteristics of the separator. From a design standpoint, the all liquid case provides a minimum flow rate for successful phase separation. Maximum flow rate depends on the pressure resources of the system.

This study was motivated by airframe noise in aircraft and blade-vortex interaction (BVI) noise in helicopters. In this thesis, the sound generated by vortical disturbances in a subsonic flow around solid surfaces, using different vortex velocity formulations, was investigated by numerically solving the linearized or non-linearized Euler equations. Analytical solutions for this general case are not available because the wavelength of the generated acoustic wave is comparable to the vortex size, which is at variance to the compact source assumption of the acoustic analogy. Numerical errors associated with the discretization and boundary conditions were kept small using a high-order scheme with accurate non-reflecting boundary conditions. Stagnation flow on a flat plate, flow around a stationary and rotating cylinder, and that about two cylinders were taken as prototypes of real-world flows with strong gradients of mean pressure and velocity. Single and periodic vortices were taken into consideration. In addition, the effect of vortex core size, the street distance, street frequency, and the Mach number of the mean flow on sound generation and propagation were examined. The sound wave strength was found to be proportional to the vortex strength. If the acoustic pressure is normalized by the vortex strength, then all the distinct acoustic pressure profiles will collapse into single curve. Sound generation by vortex interaction with a solid surface, as well as its propagation, were found to be totally different between the Taylor's and Vatistas's vortices. The vortex core size and vortex street distance have minor influences on the acoustic pressure profile for sound waves radiated by the Vatistas vortex. Nevertheless, the change of the core size or the distance between the vortex rows significantly affects the sound pressure profile and sound directivity radiated by a Taylor vortex. The effects of the non-linear terms on sound wave properties were also investigated. The non-linear influence was found to increase with the vortex strength. A lifting cylinder is shown not only to increase the sound wave amplitude, but also to shift its directivity. The developed methods and computer codes can be used in the future as platforms to more elaborate methods that will predict the noise generated by multi-element airfoils, and the undercarriage of an aircraft. This will help reduce the need of costly, time consuming, wind tunnel and field experiments.

Indiana University-Purdue University Indianapolis (IUPUI)
We numerically investigate the underlying physics of two peculiar phenomena, which are axis-switching and saddle-back velocity profile, in both laminar and turbulent rectangular jets using lattice Boltzmann method (LBM). Previously developed computation protocols based on single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann equations are utilized to perform direct numerical simulation (DNS) and large eddy simulation (LES) respectively. In the first study, we systematically study the axis-switching behavior in low aspect-ratio (AR), defined as the ratio of width over height, laminar rectangular jets with AR=1 (square jet), 1.5, 2, 2.5, and 3. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the streamwise velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. The 45° and 90° axis-switching occur in characteristic decay (CD) region consecutively at the early and late stage. The half-width contour (HWC) reveals that 45° axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when 45° axis-switching occurs. The close examinations of flow pattern and vorticity contour, as well as the correlation between streamwise velocity and vorticity, indicate that 90° axis-switching results from boundary effect. Specific flow patterns for 45° and 90° axis-switching reveal the mechanism of the two types of axis-switching respectively. In the second study we develop an algorithm to generate a turbulent velocity field for the boundary condition at jet inlet. The turbulent velocity field satisfies incompressible continuity equation with prescribed energy spectrum in wave space. Application study of the turbulent velocity profile is on two turbulent jets with Re=25900. In the jets with AR=1.5, axis-switching phenomenon driven by the turbulent inlet velocity is more profound and in better agreement with experimental examination over the laminar counterpart. Characteristic jet development driven by both laminar and turbulent inlet velocity profile in square jet (AR=1) is also examined. Overall agreement of selected jet features is good, while quantitative match for the turbulence intensity profiles is yet to be obtained in future study. In the third study, we analyze the saddle-back velocity profile phenomenon in turbulent rectangular jets with AR ranging from 2 to 6 driven by the developed turbulent inlet velocity profiles with different turbulence intensity (I). Saddle-back velocity profile is observed in all jets. It has been noted that the saddle-back's peak velocities are resulted from the local minimum mixing intensity. Peak-center difference &Delta_pc and profound saddle-back (PSB) range are defined to quantify the saddle-back level and the effects of AR and I on saddle-back profile. It is found that saddle-back is more profound with larger AR or slimmer rectangular jets, while its relation with I is to be further determined.

Electrical energy supply in South Africa, provided by ESKOM, has become more expensive with regular price increases in the past seven years. Increases on an annual basis have seen the Mega flex tariffs quadruple in the years from 2007 to 2014. ESKOM is the sole supplier of electricity to Safripol, a polymer producer of which the manufacturing facility is located in Sasolburg, South Africa. This study will provide contextual information on what impact the escalation in cost of this utility has on the financial returns of the business. Independent power generation within the boundaries of the manufacturing site has become essential in order to alleviate the impact of inflated electricity costs, by at least 10% of the current total demand from ESKOM. Primary research includes different types of alternative electricity generation techniques that will be able to deliver a practical solution to the business. The means of operation, required resources and cost to produce are set out to provide input into concrete models that are scaled to the potentials applicable to the production facility. Total alternative electricity generation added up to almost half of the current total site electricity demand from ESKOM. This finding was truly beyond the expectations of the case study and clearly set out how understated the potential to generate electricity is within the industrial sector.
MIng (Development and Management Engineering), North-West University, Potchefstroom Campus, 2015