L'injection d'un mélange carburant/comburant dans une chambre de combustion d'un turboréacteur ou d'un moteur-fusée fait intervenir un jet liquide, cisaillé par un gaz rapide. Le jet liquide peut être sous certaines conditions sujet à un phénomène de battement à grande échelle. Ce phénomène, dont les mécanismes de base sont aujourd'hui mal connus, peut avoir des conséquences importantes sur la combustion. Nous réalisons dans ce travail une étude numérique de jets liquides cisaillés par une phase rapide, en portant une attention particulière à l'étude de l'interaction entre les structures tourbillonnaires de la phase rapide et le jet liquide. Une nappe liquide plane cisaillée de part et d'autre par une phase rapide est analysée dans un premier temps . Les mécanismes de déstabilisation de cette nappe liquide sont étudiés, ainsi que le contrôle passif du phénomène de battement. Des jets liquides coaxiaux, cisaillés par une couronne de phase rapide, sont ensuite analysés. Les mécanismes de déstabilisation à grande échelle sont étudiés, ainsi que le contrôle passif et actif de cette déstabilisation. La simulation d'une configuration d'écoulement réaliste eau/air est enfin réalisée, en interaction avec les expérimentateurs du LEGI. Une attention particulière est portée à l'écoulement se produisant au sein de la buse d'injection. / Fuel injection in an aircraft engine or in a rocket engine involves a liquid jet sheared by a high-velocity gas. The liquid jet can display, under some specific conditions, a flapping motion. This flapping motion, the basic mechanisms of which are still poorly understood, can significantly impact the combustion process. We perform in this work a numerical study of liquid jets interacting with a high-speed stream and focus on the interactions between the vortical structures in this high-speed stream and the liquid jet. A plane liquid jet surrounded by two high-speed streams is first analysed. The mechanisms leading to the flapping motion are studied, as well as the passive control of this instability. A liquid coaxial jet, sheared by an annular high speed stream, is next analysed. The mechanisms leading to the flapping motion are also analysed, as well as passive and active strategies for controlling this instability. Finally, we perform simulations of an experimental set-up studied at LEGI, focusing on the flow inside the nozzle.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Through the Karoo Array Telescope, and its extension MeerKAT, South Africa is demonstrating its capabilities to host the most powerful radio telescope ever, the Square Kilometre Array (SKA). This new interferometer is intended to assist radio astronomers in unlocking the mysteries concealed in the far regions of the universe. A thorough investigation of Radio Frequency Interference (RFI) sources at each stage of the design becomes relevant for the success of the project. The electromagnetic coupling through coaxial cables is the main focus of this thesis since 90% of the Electromagnetic Compatibility (EMC) problems come from inadequate system layout and grounding, where cabling plays the major role. Interest revolves around better noise immunity, low radiation and cost. Transfer impedance (ZT ) and shielding e ectiveness (SE) are used as the cable selection criteria. Several measurements of coaxial cables identi ed on KAT-7 have been performed for ZT characterisation from 300 kHz up to 1.3 GHz. A current injection method is used to identify the ZT for the low frequency region. We derived the high frequency part of ZT , with a reverberation chamber technique (RC) measuring shielding e ectiveness. At rst, we calibrated the RC according to the relevant IEC 61000-4-21 standard and evaluated the result with an Open Area Test Site (OATS) E- eld estimation. The accuracy of the E- eld within the chamber is also addressed, based on statistical analysis of the chamber's independent samples. The OATS E- eld equivalent determination showed a good correlation with the OATS E- eld data of a standard radiator. A coaxial air-line ZT veri ed the theoretical ZT model within 7 dB and showed the expected 20 dB/decade slope variation. Furthermore, the braiding porpoising e ect has been noticed with some cable samples. Here, a variation less than 20 dB/decade occurs at lower frequency. Then, the slope changes to 20 dB/decade at high frequency. This study illustrates a practical comparison of cable performance and constitutes a rst approach to RFI mitigation of the MeerKAT cabling system. / AFRIKAANSE OPSOMMING: Deur middel van die Karoo Reeks Teleskoop, asook sy uitbreiding MeerKAT, demonstreer Suid-Afrika sy vermo om die mees kragtige radioteleskoop ooit, die Vierkante Kilometer Reeks (SKA), te vestig. Hierdie nuwe interferometer is bedoel om radiosterrekundiges te help in die ontsluiting van die geheimenisse wat versteek is in die verre reike van die heelal. 'n Deeglike ondersoek van Radio Frekwensie Steurings (RFS) bronne by elke stadium van die ontwerp is belangrik vir die sukses van die projek. Die elektromagnetiese koppeling deur koaksiale kabels is die hoo okus van hierdie tesis, aangesien 90% van die elektromagnetiese versoenbaarheid (EMV) probleme ontstaan as gevolg van onvoldoende stelsel-uitleg en beaarding, waar kabels die hoofrol speel. Beter ruis-immuniteit, lae straling en koste vorm die areas van belang. Oordragimpedansie (ZT ) en afskermingsdoeltre endheid (SE) word gebruik as die kabelkeuringskriteria. Verskeie metings van koaksiale kabels wat op KAT-7 gedenti seer is, is uitgevoer vir ZT karakterisering van 300 kHz tot 1,3 GHz. 'n Stroom-induseringsmetode is gebruik om die ZT vir die lae-frekwensiebereik te identi seer. Ons het die ho-frekwensie deel van ZT afgelei met 'n weerkaatsingskamer tegniek (RC) wat afskermingsdoeltre endheid meet. Eerstens het ons die RC gekalibreer volgens die relevante IEC 61000-4-21 standaard en die resultaat met 'n Ope Area Toetsterrein (OAT) E-veld benadering gevalueer. Die akkuraatheid van die E-veld in die kamer is ook aangespreek, gebaseer op 'n statistiese analise van die kamer se onafhanklike monsters. Die OAT E-veld ekwivalente benadering het goed met die OAT E-veld data van 'n standaard uistraler gekorreleer. 'n Koaksiale lugmedium-transmissielyn ZT bevestig die teoretiese ZT model binne 7 dB en het ook die verwagte 20 dB/dekade variasie in helling getoon. Verder is die golwende e ek oor die kabelomvlegting opgemerk met sekere kabels. Hier is 'n variasie van minder as 20 dB/dekade gevind by die laer frekwensie. Dan verander die helling na 20 dB/dekade teen ho frekwensie. Hierdie studie toon 'n praktiese vergelyking van die verrigting van die kabel en 'n eerste benadering tot RFS tempering van die MeerKAT kabelstelsel.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The purpose of this project is to develop a number of coaxial resonator lters. Firstly, the theoretical model of the lter is discussed, with a Tchebyscheff LC-ladder prototype lter used to derive a generalised bandpass lter. From this, generalised Combline- and Interdigital lters are derived. Following this, various options and limitations in the mechanics of microwave lters are discussed. Results are shown for an in-depth study considering the unloaded quality factor for thirteen di erent resonators. Each resonator is unique in the method of manufacturing, polishing, as well as plating. Utilizing the information obtained from the unloaded quality factor measurements, three coupled coaxial resonator lters, are designed for use in a radar system, namely a sixth order 2125 MHz Combline lter, a sixth order 9250 MHz Interdigital lter and a third order 9250 MHz Interdigital lter. Optimal results were obtained when both resonators and coupled transmission line lters were constructed from aluminium that was wire-cut and then silver electroplated. / AFRIKAANSE OPSOMMING: Die omvang van hierdie projek behels die ontwerp en bou van ko-aksiale resoneerder filters. Eerstens word die teoretiese modellering van die lters bespreek. 'n Tchebyscheff LC-leer prototipe filter word gebruik as basis vir 'n generiese banddeurlaat filter. Die banddeurlaat lter word gebruik om die afgeleide Kamlyn- en Interdigitale filter te de finieer. Hierna volg 'n bespreking aangaande die verskillende moontlikhede in die meganiese vervaardiging van mikrogolf filters. 'n Gedetailleerde studie word gedoen om die onbelaste kwaliteitsfaktore van 13 verskillende resoneerders te bepaal. Elkeen van hierdie resoneerders is uniek in die metode van vervaardiging, polering, asook die platering daarvan. Deur gebruik te maak van die resultate van die onbelaste kwaliteitsfaktore, word drie gekoppelde ko-aksiale resoneerder filters ontwikkel vir die gebruik in 'n radarstelsel, naamlik 'n sesde-orde 2125 MHz Kamlyn lter, 'n sesde orde 9250 MHz Interdigitale filter, asook 'n derde orde 9250 MHz Interdigitale filter. Die beste resultate was gevind toe beide resoneerders en gekoppelde ko-aksiale resoneerder filters vervaardig is uit aluminium wat gedraadsny en silwer geplateer is.

<p> Lifted non-premixed turbulent jet flames in the Transverse Instability Combustor (TIC) have been analyzed using qualitative and quantitative methods. Lifted flames in the TIC have been observed to stabilize about zero to five injector exit diameters downstream of the dump plane into the chamber and exhibit pulsating, unsteady burning. Anchored flames immediately begin reacting in the injector recess and burn evenly in a uniform jet from the injector exit through the entire optically accessible region. Statistically significant, repeatable behavior lifted flames are observed. It is shown that the occurrence of lifted flames is most likely for an injector configuration with close wall-spacing, second greatest for a configuration with close middle-element spacing, and lowest for a configuration with even element-spacing. For all configurations, of those elements that have been observed to lift, the center element is most likely to lift while the second element from the wall was likely. Flames at the wall elements were never observed to lift. Evidence is shown to support that close injector element spacing and stronger transverse pressure waves aid lateral heat transfer which supports flame stability in the lifted position. It is hypothesized that the stability of lifted flames is influenced by neighboring ignition sources, often a neighboring anchored flame. It is also shown that instances of lifted flames increase with the root-mean-squared magnitude of pressure fluctuation about its mean (P’ RMS) up to a threshold, after which flames stabilize in the anchored recess position.</p> <p>Dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) analyses of CH* chemiluminescence data is performed. It is found that lateral ignition of the most upstream portion of lifted flames is dominated by the 1W mode. Furthermore, it is shown that low-frequency high energy modes with spatial layers resemble intensity-pulses, possibly attributable to ignition. These modes are trademarks of CH* chemiluminescent intensity data of lifted flames. It was also shown that the residence time in the chamber may be closely associated with those low-frequency modes around 200 Hz. DMD and POD were repeated for a downstream region on the center element, as well as a near-wall element, highlighting differences between the lifted flame dynamics in all three regions. </p> <p>It is shown that lifted flames are best characterized by their burning behavior and in rare cases may stabilize in the recess, while still being “lifted”. Furthermore, it is shown that flame position differentiation can extend into an initial period of highly stable combustor operation. Dynamic mode decomposition is explored as potential method to understand physical building blocks of proper orthogonal spatial layers. Non-visual indicators of lifted flames within the high-frequency (HF) pressure signal are sought to seek a method that allows for observation of lifted flames in optically inaccessible combustors, such as those in industry. Some attributes of power-spectral diagrams and cross-correlations of pressure signals are provided as potential indicators. </p>

This thesis examines the development of DC-DC converters that are suitable for Module Integrated Converters, (MICs), in grid interactive photovoltaic (PV) systems, and especially concentrates on the study of the half bridge dual converter, which was previously developed from the conventional half bridge converter. Both hard-switched and soft-switched half bridge dual converters are constructed, which are rated at 88W each and transform a nominal 17.6Vdc input to an output in the range from 340V to 360Vdc. An initial prototype converter operated at 100kHz and is used as a base line device to establish the operational behaviours of the converter. The second hard-switched converter operated at 250kHz and included a coaxial matrix transformer that significantly reduced the power losses related to the transformer leakage inductance. The soft-switched converter operated at 1MHz and is capable of absorbing the parasitic elements into the resonant tank. Extensive theoretical analysis, simulation and experimental results are provided for each converter. All three converters achieved conversion efficiencies around 90%. The progressive increases in the operation frequency, while maintaining the conversion efficiency, will translate into the reduced converter size and weight. Finally different operation modes for the soft-switched converter are established and the techniques for predicting the occurrence of those modes are developed. The analysis of the effects of the transformer winding capacitance also shows that soft switching condition applies for both the primary side mosfets and the output rectifier diodes.

The aim of this study is to demonstrate the possibility of production of nanocables as an alternative to the other one dimensional metal/polymer composite structures like nanowires and nanorods. There is no certain definition of nanocables / however they could be considered as assemblies of nanowires. Nanocable structure can be defined as a core-shell structure formed by a polymeric shell and a metal core that runs continuously within this shell. To produce nanocables, two main steps were carried out. Firstly, monodispersed silver metal nanoparticles to be aligned within the cable core were produced. Investigations on reduction reactions in the presence of strong and weak reducing agents and different capping agents revealed the importance of the kinetics of reduction in the production of monodispersed nanoparticles. Use of capping agents to give a positive reduction potential, resulted in the slow reduction rates that was critical for fine tuning of the final particle sizes between 1-10 nm. Hydrazine hydrate and oleylamine/ oleic acid systems were used as strong and weak reducing agents, respectively. By using weak reducing agent, monodisperse spherical silver nanoparticles with the diameter of 2.7 nm were produced. It was shown that particles with controlled diameter and size distribution can be obtained by tuning the system parameters. Secondly, particles produced as such were electrospun within the core of the polymer nanofibers and long continuous nanocables were produced. Polyvinyl pyrrolidone and polycaprolactone were used in shell part of nanocables. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), X-ray diffraction (XRD) and surface plasmon resonance spectroscopy (SPR) analyses were carried out in order to understand the mechanism by which the nanoparticles were reduced and for further characterization of the product.

Differential Mobility Spectrometry (DMS) using a non-radioactive ion source (NRIS) is investigated as a possible medical diagnostic instrument for near real-time detection of breast cancer biomarkers. In previous clinical studies, concentrations of Linoleic, Palmitic and Stearic fatty acids have been observed at different levels in women with carcinoma breast cancer versus women with benign tumors or healthy women showing no signs of breast cancer. Present diagnostic methods require a biopsy of the suspect tissue and a microscopic lab analysis performed to determine its disease state. This process can take hours or days before the patient and doctor are informed of the results. Controlled volumetric samples of each fatty acid listed above were introduced into a DMS instrument, using a NRIS, to determine detectability of each acid. The results provide proof-of-concept that Linoleic, Palmitic and Stearic fatty acids can be uniquely identified by varying the sample temperature and scanning the ionized fatty acid molecules in both the negative and positive ion mode of the DMS instrument. Detection response times range from 2 to 6 seconds for initial detection up to 35 seconds for peak detection. The Limit of Detection for the DMS instrument is estimated in the low parts per billion.

The aim of this master’s theses was a designing of duplexer working in non license frequency band 5.6GHz. The theses is concerning with selection of suitable concept for a given duplexer, with creating a model in software for simulation of distribution of electromagnetic field and with subsequent implementation of duplexer and verifying its parameters.

This thesis deals with the analysis of coaxial cavity filters and synthesis of generic topology of these filters. Transfer function comes out the synthesis, which is based on low-pass prototype and similarity with real structure. The next aim of this thesis is to build the basic software for coaxial cavity filters synthesis from engaged characteristic parameters of the filter. This work also includes the analysis of coupling matrix synthesis based on transfer function, where we can use direct coupling or cross-coupling between resonators. The last point is focused on the diplexer filter based on specified parameters and obtained coupling matrix. Entire diplexer model is optimized using Tuning-Space Mapping method.

This thesis describes possibilities of measuring permittivity of various materials, especially with coaxial probe method. It describes character of measuring method, hardware requirements and how to calculate values from the measured. Objective of this thesis is to design measuring station for measuring permittivity of materials with coaxial probe including calibration set. Code in Matlab is also programmed and whole station is tested with known samples to discuss measurement accuracy.