Дисертації з теми "SwIRa"
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1
Ben-Yeoshua, Moshe 1957. "Coaxial jets with swirl." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/291734.
Повний текст джерелаАнотація:
The near field of coaxial air jets, with swirl in the outer one, was investigated experimentally. Axial and azimuthal velocities were mapped using hot-wire anemometry, and static pressure measurements were obtained using a pitot tube. The flow was visualized using a double-pass schlieren system. The flow is sensitive to both the amount of swirl, characterized by the swirl number S, and the mass flow ratio between the outer and inner jets, mr. A necessary condition for recirculation to occur was that S > 0.58 and mr > 8.5. The magnitude of a pressure deficit in the centerline strongly depends on mr, while the existence of swirl appears to have a triggering effect on setting up this pressure gradient. Spectral analysis shows distinct characteristics dependent on the occurrence of recirculation. Because these features were observed upstream of the recirculation region, the vortex breakdown in this experiment may be related to flow instabilities.
2
Yellugari, Kranthi. "Effects of Swirl Number and Central Rod on Flow in Lean Premixed Swirl Combustor." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563872979440851.
Повний текст джерела
3
Ayache, Simon Victor. "Simulations of turbulent swirl combustors." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243609.
Повний текст джерелаАнотація:
This thesis aims at improving our knowledge on swirl combustors. The work presented here is based on Large Eddy Simulations (LES) coupled to an advanced combustion model: the Conditional Moment Closure (CMC). Numerical predictions have been systematically compared and validated with detailed experimental datasets. In order to analyze further the physics underlying the large numerical datasets, Proper Orthogonal Decomposition (POD) has also been used throughout the thesis. Various aspects of the aerodynamics of swirling flames are investigated, such as precession or vortex formation caused by flow oscillations, as well as various combustion aspects such as localized extinctions and flame lift-off. All the above affect flame stabilization in different ways and are explored through focused simulations. The first study investigates isothermal air flows behind an enclosed bluff body, with the incoming flow being pulsated. These flows have strong similarities to flows found in combustors experiencing self-excited oscillations and can therefore be considered as canonical problems. At high enough forcing frequencies, double ring vortices are shed from the air pipe exit. Various harmonics of the pulsating frequency are observed in the spectra and their relation with the vortex shedding is investigated through POD. The second study explores the structure of the Delft III piloted turbulent non-premixed flame. The simple configuration allows to analyze further key combustion aspects of combustors, with further insights provided on the dynamics of localized extinctions and re-ignition, as well as the pollutants emissions. The third study presents a comprehensive analysis of the aerodynamics of swirl flows based on the TECFLAM confined non-premixed S09c configuration. A periodic component inside the air inlet pipe and around the central bluff body is observed, for both the inert and reactive flows. POD shows that these flow oscillations are due to single and double helical vortices, similar to Precessing Vortex Cores (PVC), that develop inside the air inlet pipe and whose axes rotate around the burner. The combustion process is found to affect the swirl flow aerodynamics. Finally, the fourth study investigates the TECFLAM configuration again, but here attention is given to the flame lift-off evident in experiments and reproduced by the LES-CMC formulation. The stabilization process and the pollutants emission of the flame are investigated in detail.
4
Pantelides, Kyriacos. "Isothermal and combusting swirl-stabilised." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397059.
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5
Ahmad, N. T. "Swirl stabilised gas turbine combustion." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356423.
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6
Zannoni, Marco. "Simulazione dinamica swirl in motore diesel." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9268/.
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7
Kashdan, Julian Takashi. "Experiments on intermittent swirl generated sprays." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252188.
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8
Shelil, Nasser. "Flashback studies with premixed swirl combustion." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/55494/.
Повний текст джерелаАнотація:
The important conclusion was reached that when combusting H2/CH 4 fuel mixes flashback behaviour approaches that of pure methane for equivalence ratios less than about 0.65, all pressures investigated up to 7 bara and air inlet temperatures of 300 and 473K. Significant deleterious changes in flashback behaviour for H2/CH4 fuel mixes occurred for air inlet temperatures of 673K, although operation at weak equivalence ratios less than 0.65 was still beneficial.
9
DUARTE, LUIZ GUSTAVO DA CRUZ. "MASS TRANSFER TO SWIRL IMPINGING JETS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1994. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24868@1.
Повний текст джерелаАнотація:
O presente trabalho é um estudo experimental das características de troca de calor e massa de um jato de ar incidindo ortogonalmente sobre uma placa. o estudo tem por objetivo avaliar a influência nos coeficientes de troca da presença de um componente circunferencial na velocidade do jato. Durante os experimentos foram investigadas a influência do número de Reynolds do jato, da distância jato/placa e da intensidade do escoamento espiralado (número de swirl).
Os coeficientes de troca foram determinados utilizando-se a técnica de sublimação de naftaleno em conjunto com a analogia entre os provessos de transferência de calor e massa. Coeficientes de troca de massa locais foram determinados utilizando-se uma mesa de coordenadas computadorizada especialmente construída, que permitiu a obtenção de medidas detalhadas tanto na região de estagnação do jato quanto na região mais externa. Coeficientes globais de troca de massa foram obtidos independentemente dos locais através de pesagem.
Os resultados demonstraram uma diminuição nos coeficientes de troca de massa do jato com o aumento da intensidade do escoamento espiralado.
Visualizações do escoamento junto à placa foram realizadas, utilizando-se a técnica de óleo com o negro de fumo. Os resultados das visualizações demonstraram a existência de regiões de separação junto à fronteira da zona de estagnação. Para altos valores do número de swirl foram verificadas fortes reversões do escoamento na região de estagnação.The present work is an experimental study of the mass transfer characteristics of a swirling jet impinging on a flat plate. The main objective of the investigation was to determine the influence of a circumferential velocity component (the swirl component) on the local and average mass transfer coefficients at the plate surface. The dimensionless parameters investigated were the jet Reynolds number, the jet-to-plate distance, and the strength of the swirl flow given by the swirl number. Mass transfer coefficients were obtained utilizing the naphthalene sublimation technique. The local coefficients were determined employing a computerized coodinate table which allowed a detailed study of the effects of the presence of the swirl component. Average coefficients were determined independently through precision weighing, and displayed excellent agreement with the integrated local coefficients. The results demonstrated that the presence of the swirl component decreases the mass transfer coefficients, when compared with the non-swirl case. Flow visualization experiments were conducted utilizing the oil-lamp black technique. The results revealed regions of reverse flow at the stagnation zone for high values of the swirl number.
10
Hoopes, Kevin M. "A New Method for Generating Swirl Inlet Distortion for Jet Engine Research." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/49545.
Повний текст джерелаАнотація:
Jet engines operate by ingesting incoming air, adding momentum to it, and exhausting it through a nozzle to produce thrust. Because of their reliance on an inlet stream, jet engines are very sensitive to inlet flow nonuniformities. This makes the study of the effects of inlet nonuniformities essential to improving jet engine performance. Swirl distortion is the presence of flow angle nonuniformity in the inlet stream of a jet engine. Although several attempts have been made to accurately reproduce swirl distortion profiles in a testing environment, there has yet to be a proven method to do so.A new method capable of recreating any arbitrary swirl distortion profile is needed in order to expand the capabilities of inlet distortion testing. This will allow designers to explore how an engine would react to a particular engine airframe combination as well as methods for creating swirl distortion tolerant engines. The following material will present such a method as well as experimental validation of its effectiveness.
Master of Science
11
Prassas, Ilias. "Combustion of pulverised coal in swirl burners." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286343.
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12
Novotny, Pavel [Verfasser]. "Stability of Swirl Tube Flow / Pavel Novotny." München : Verlag Dr. Hut, 2019. http://d-nb.info/1200755308/34.
Повний текст джерела
13
Yapici, Sinan. "Electrochemical mass transfer in annular swirl flow." Thesis, University of Exeter, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303777.
Повний текст джерела
14
Hatem, Fares. "Flashback analysis and avoidance in swirl burners." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/103700/.
Повний текст джерелаАнотація:
This study is aimed to investigate and demonstrate the feasibility and validity of various flame flashback resistance techniques for premixed fuel conditions. It presents a series of experiments to determine the impact of different configurations on flame flashback mechanisms. Experiments were performed using a 150 kW tangential swirl burner working on premixed mode with various swirl numbers; the flow field characteristics were measured by 1D LDA. The first part of the project targeted the effect of central fuel injector geometries on flame flashback mechanisms, especially combustion induced vortex breakdown (CIVB). It was found that changing the central fuel injector outside diameter can significantly alter the flame flashback mechanism. Large injector diameters result in boundary layer flashback (BLF), contrary, the use of small injectors diameter led to CIVB. Thus a dimensionless number (χ) which represent the ratio between the injector outside diameter and the nozzle inside diameter was introduced. Using this dimensionless number the critical value of transition from CIVB to BLF has been defined, the value being χ= 0.280 for Sg=1.12 and χ= 0.320 for Sg= 0.9. The second part was about the effect of using axial air injection instead of central fuel injectors. It was found that axial air jets have a considerable potential for flame stability requirements, they producing wider stability operation than that of central injectors. Moreover, the stability limits increase regarding both equivalence ratio and inlet tangential velocity. It appeared that using such air jets could reduce the combustor maintenance cost that arises due to a continuous harsh environment. However, it was found that axial air jets could enforce flame propagation during flashback via wall boundary layer. Thus, the third part of the study was about the validity of using micromeshes to improve BLF resistance in addition to axial air injection. It was found that using both techniques produced high flashback resistance for both mechanisms, i.e. CIVB and BLF.
15
Nehring, Wendy M. "Nursing leadership during a time of swirl." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/6721.
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16
Islek, Akay A. (Akay Aydin). "The Impact of Swirl in Turbulent Pipe Flow." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4955.
Повний текст джерелаАнотація:
The impact of swirl (i.e., flow with axial and azimuthal velocity components) on the turbulent flow in a pipe is studied using two-component laser-Doppler velocimetry (LDV). There are practical motivations for the flow geometry. For example, previous studies demonstrate that introducing swirl in the tube bank of a paper machine headbox can significantly increase mixing, and hence increase fiber dispersion and orientation isotropy in the finished paper product. The flow characteristics in a pipe downstream of a single straight tapered fin, a single fin with 180??ist but otherwise identical geometry, and four twisted fins were therefore studied at a pipe-based Reynolds number of 80,000. Radial profiles of the mean and rms fluctuations of the streamwise and azimuthal velocity components are measured; results for the straight and twisted single fin are compared to determine the effects of fin geometry and swirl on the turbulent wake downstream of the fin. From a practical viewpoint, it is also desirable to have adjustable swirl, where swirl can either be turned on or off depending upon the type of paper product being produced. The next generation swirler concept consists of fins fabricated from two-way shape memory alloys. Using the two-way memory effect, the fins will be in their straight configuration when cold and twisted configuration (hence acting as a swirler) when hot. This study is the initial phase in developing new active control mechanisms, known as the Vortigen concept, for increasing productivity, and hence reducing wasted raw material and energy, in the pulp and paper industry.
17
Prakash, Shashvat. "Lean Blowout Mitigation in Swirl Stabilized Premixed Flames." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16159.
Повний текст джерелаАнотація:
Lean, premixed combustion offers a practical approach for reducing nitrogen oxide (NOx) emissions, but increases the risk of lean blowout (LBO) in gas turbines. Active control techniques are therefore sought which can stabilize a lean flame and prevent LBO. The present work has resulted in the development of flame detection, dynamic modeling, blowout margin estimation, and actuation and control techniques. The flame s acoustic emissions were bandpass filtered at select frequencies to detect localized extinction events, which were found to increase in number near LBO. The lean flame was also found to intermittently burst into a transient tornado configuration in which the flame s inner recirculation zone would collapse. The localized extinctions were dynamically linked to the tornado bursts using a linear, first order model. The model was subsequently applied to predict tornado bursts based on optically detected localized extinction events. It was found that both localized extinctions and tornado bursts are by themselves Poisson processes; the exponential distribution of their spacing times could be used to determine blowout probability. Blowout mitigation was achieved by redistributing the fuel flow between the annular swirlers and central preinjection pilot, both of which were premixed. Rule-based and lead-lag control architectures were developed and validated.
18
Fiskum, Andreas. "Calculation of NOx Formation in a Swirl Burner." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12869.
Повний текст джерелаАнотація:
This thesis embraces simulations of NOx emissions from a partially premixed 20 kW swirl burner. The simulations were carried out in the commercial computational fluid dynamics software FLUENT. The concept of partial premixing air and fuel before adding additional air for complete combustion has proven promising with a view on the NOx emissions. However, little research has been done on reach premixing of fuel and air and therefore further investigation of this topic is of interest. In most experiments in the literature methane is used as fuel, but due to problems with stability and blow off in the 20 kW swirl burner propane were chosen as fuel.Simulations of eight different air-fuel ratios have been performed, ranging from diffusion flame to a mass based air-fuel ratio of four. The results from these simulations proved satisfactory when comparing with previous experimental and simulated work, except from the calculations of the exact NOx concentration. This difference in the concentration was one the other hand expected since the power of FLUENT and similar software is to predict variation trends and not the exact value itself.The simulations showed that the NOx concentration increased with increasing premixing, reaching a local peak at an air-fuel ratio of two. After this a local minimum in the NOx concentration was observed before a strong increase when further raising the air-fuel ratio. This is the same trends that are observed in the literature when using methane as fuel, but for propane there is no global reduction in the NOx emissions when applying premixing. This increase in the NOx emission was found to be due to an expansion of the high temperature flame zone with increasing premixing, which benefits the thermal NOx formation mechanism. The NOx reducing effect of swirl generation observed to decrease when the air-fuel ratio was increased. For subsequent experimental work it is recommended to perform a high amount of experiments at different air-fuel ratios, especially in the ratio range where the NOx concentrations starts to fluctuate.
19
Bonaldo, Alessio. "Experimental Characterisation of Swirl Stabilized Annular Stratified Flames." Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/3171.
Повний текст джерелаАнотація:
A burner for investigating lean stratified premixed flames propagating in intense
isotropic turbulence has been developed. Lean pre-mixtures of methane at different
equivalence ratios are divided between two concentric co-flows to obtain annular
stratification. Turbulence generators are used to control the level of turbulence intensity
in the oncoming flow. A third annular weakly swirling air flow provides the flame
stabilization mechanism. A fundamental characteristic is that flame stabilization does
not rely on flow recirculation. The flames are maintained at a position where the local
mass flux balances the burning rate, the result is a freely propagating turbulent flame
front. The absence of physical surfaces in the vicinity of the flame provides free access
for laser diagnostics.
Stereoscopic Planar Image Velocimetry (SPIV) has been applied to obtain the three
components of the instantaneous velocity vectors on a vertical plane above the burner
outlet where the flames propagate. The instantaneous temperature fields have been
determined through Laser Induced Rayleigh (LIRay) scattering. Planar Laser Induced
Fluorescence (PLIF) on acetone has been used to calculate the average equivalence ratio
distributions. Instantaneous turbulent burning velocities have been extracted from SPIV
results, while flame curvature and flame thermal thickness values have been calculated
using the instantaneous temperature fields. The probability distributions of these
quantities have been compared considering the separate influence of equivalence ratio
stratification and turbulence. It has been observed that increased levels of turbulence
determine higher turbulent burning velocities and flame front wrinkling. Flames
characterized by stronger fuel stratification showed higher values in turbulent burning
velocities. From the curvature analysis emerged that increased fuel concentration
gradients favour flame wrinkling, especially when associated with positive small radius
of curvature. This determines an increased surface area available for reaction that
promotes a faster propagation of the flame front in the oncoming combustible mixtures.
20
Baker, Philip. "Investigation of barrel swirl in spark ignition engines." Thesis, Coventry University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364160.
Повний текст джерела
21
Frost, Mark I. "The clustering of galaxies in the SWIRE survey." Thesis, University of Sussex, 2010. http://sro.sussex.ac.uk/id/eprint/2363/.
Повний текст джерелаАнотація:
Despite the coherent cosmological framework provided by the λCDM model that astronomers have to work within, there are still a lot of unanswered questions regarding galaxy formation and evolution. Measuring the clustering of galaxies can provide information about the different environments that different types of galaxies reside in. Also, measuring the clustering of similar samples of galaxies at different redshifts can provide insights into how galaxies have evolved over time. Previous clustering analyses, particularly at high redshift, have often been restricted to galaxy samples which are small, selected on observable properties and/or contain an unknown mixture of different spectral types. Small samples lead to limited statistics and the inability to break the sample into interesting subsamples based on properties, e.g. by luminosity or star formation rate. Selecting samples based on observable properties leads to varying intrinsic properties with redshift and hence makes interpreting the evolution of clustering difficult. Mixing spectral types makes it impossible to separate the contribution to the clustering signal from early and late-type galaxies which tend to cluster very differently. This thesis overcomes some of the limitations of earlier clustering analyses by using the Spitzer Wide area InfraRed Extragalactic (SWIRE) photometric redshift catalogue of Rowan-Robinson et al.(2008) to measure the clustering of galaxies. The SWIRE catalogues covered multiple fields and large volumes providing large samples of galaxies over 0.1 < z < 1.5. The template fitting procedure also provides spectral classifications as well as intrinsic properties such as stellar mass and star formation rate estimates. The clustering of elliptical and spiral galaxies detected in SWIRE is measured as a function of stellar mass over 0.1 ≤ z ≤ 1.5. The clustering of spiral galaxies selected on star formation rate is also investigated over the same redshift range. Such measurements can help constrain theories of galaxy evolution. Another Spitzer dataset, the dark field, is used in an attempt to place one of the first observational constraints on the detection rate of population III supernovae. The dark field is an extragalactic data set with repeat imaging on a monthly basis over a baseline of approximately 2 years. The unprecedented depth and multi-epochal nature of this data makes it ideal for a first foray into trying to detect supernovae from the first stars.
22
Malý, Milan. "Internal Flow of Spill-Return Pressure-Swirl Atomizers." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-437981.
Повний текст джерелаАнотація:
Tlakové vířivé trysky (TVT) jsou používané v mnoha aplikacích, kde je potřebná velká plocha kapek nebo kde povrch musí být nanesen kapalinou, např. spalování, sprejové chlazení nebo nanášení barev. Parametry spreje z TVT jsou úzce spojené s jejich vnitřním prouděním. Obtokové trysky vylepšují koncepci klasických TVT přítomností otvoru, skrz který může kapalina odtékat zpět do nádrže. Díky této koncepci je možné regulovat vstřikovací množství kapaliny změnou průtoku tímto otvorem, zatímco se ve vířivé komůrce udržuje vysoký tlak, který zaručí dobrou kvalitu spreje. Obtokové trysky byly historicky málo prozkoumány a jejich vnitřní proudění nebylo studováno téměř vůbec. V této práci je popsáno vnitřní proudění několika obtokových trysek jak experimentálně, tak numericky. Tato data jsou následně korelována s měřenými vlastnostmi spreje. Výsledky ukazují, že přidání obtokového otvoru silně ovlivní vnitřní proudění i v případech, kdy obtokem neproudí žádná kapalina. V některých případech se vůbec nezformuje vzdušné jádro a tím se destabilizuje výtok z trysky, čímž vznikne nestabilní sprej. Mimoosé obtokové otvory generují a stabilizují vzdušné jádro, což pomáhá formovat kapalinovou stěnu a vysoce kvalitní sprej. Nicméně některé konfigurace změnily charakter rozpadu kapalinové stěny, což se projevilo i na kvalitě spreje. Navíc regulační schopnost a stabilita spreje závisí na vzdálenosti obtokových otvorů od osy vířivé komůrky. Na závěr byla upravena neviskózní teorie, která analyticky popisuje vnitřní proudění v TVT, tak aby byla aplikovatelná i na obtokové trysky. Pomocí tohoto přístupu byla odvozena teoretická predikce výtokového součinitele a velikosti vzdušného jádra v závislosti na obtokovém poměru (SFR). Zároveň byly pro obtokové trysky upraveny empirické korelace původně odvozené pro TVT. Tato práce přináší nový vhled k porozumění vnitřního proudění obtokových trysek a její výsledky najdou uplatnění při jejich návrhu.
23
XUE, JIANQING. "COMPUTATIONAL SIMULATION OF FLOW INSIDE PRESSURE-SWIRL ATOMIZERS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100228747.
Повний текст джерела
24
Mehdi, Ahad. "Effect of swirl distortion on gas turbine operability." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/12129.
Повний текст джерелаАнотація:
The aerodynamic integration of an aero-engine intake system with the airframe
can pose some notable challenges. This is particularly so for many military air-
craft and is likely to become a more pressing issue for both new military systems
with highly embedded engines as well as for novel civil aircraft configurations.
During the late 1960s with the advent of turbo-fan engines, industry became in-
creasingly aware of issues which arise due to inlet total pressure distortion. Since
then, inlet-engine compatibility assessments have become a key aspect of any new
development. In addition to total temperature and total pressure distortions, flow
angularity and the associated swirl distortion are also known to be of notable con-
cern. The importance of developing a rigorous methodology to understand the
effects of swirl distortion on turbo-machinery has also become one of the major
concerns of current design programmes.
The goal of this doctoral research was to further the current knowledge on
swirl distortion, and its adverse effects on engine performance, focusing on the
turbo-machinery components (i.e. fans or compressors). This was achieved by
looking into appropriate swirl flow descriptors and by correlating them against the
compressor performance parameters (e.g loss in stability pressure ratios). To that
end, a number of high-fidelity three-dimensional Computational Fluid Dynamics
(CFD) models have been developed using two sets of transonic rotors (i.e. NASA
Rotor 67 and 37), and a stator (NASA Stator 67B). For the numerical purpose,
a boundary condition methodology for the definition of swirl distortion patterns
at the inlet has been developed. Various swirl distortion numerical parametric
studies have been performed using the modelled rotor configurations. Two types of swirl distortion pattern were investigated in the research, i.e. the pure bulk
swirl and the tightly-wound vortex.
Numerical simulations suggested that the vortex core location, polarity, size
and strength greatly affect the compressor performance. The bulk swirl simula-
tions also showed the dependency on swirl strength and polarity. This empha-
sized the importance of quantifying these swirl components in the flow distortion
descriptors. For this, a methodology have been developed for the inlet-engine
compatibility assessment using different types of flow descriptors. A number of
correlations have been proposed for the two types of swirl distortion investigated
in the study.
25
Chinn, John Joss. "The internal flow physics of swirl atomizer nozzles." Thesis, University of Manchester, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488302.
Повний текст джерелаАнотація:
The internal flow of pressure swirl atomizers is studied with the ultimate aim of developing a design tool for such atomizers, particularly to enable the production of the finest possible water sprays (for any given supply pressure) for fire suppression purposes. The primary direction of the research was in computationally modelling this flow with a two-dimensional assumption and a methodology is described which is capable of determining the velocity profiles and, for the first time in the literature, the air-core topology and discharge coefficient, for nozzles which approximate the axially-symmetric condition. The results are compared with the experimental results from both the literature and also from research which was carried out under the supervision of the author. The predictions show important flow features, which are found in the experiments and have not been recognised in the "classically" assumed internal flow. These include concentration of the axial flow near the air-core and toroidal vortices, similar to Taylor-Göertler vortices found in Taylor-Couette flow, which are visible in planes through the nozzle axis. The secondary direction of the research is in both reviewing and improving upon simplified analytical techniques which have been used to estimate the size of the air-core radius at the nozzle exit together with the values of the discharge coefficient and the cone angle of the resultant spray. A critical review is given of many of the existing analytical techniques and a new analytical theory is presented which is based upon a balance of the axial momentum across a control volume. The results of the new theory are compared with the experimental findings reported in the literature and show the need to include the swirl chamber/nozzle orifice ratio as an independent variable. Suggestions are given on how the computational methodology might be employed to determine the spray drop size for a given atomizer design and on the direction the computational work might take in order to predict a full two-phase internal flow using volume of fluid (VOF) techniques.
26
Bauduin, Hadrien. "Contribution expérimentale à l'étude d'écoulements internes avec swirl." Thesis, Valenciennes, 2014. http://www.theses.fr/2014VALE0015/document.
Повний текст джерелаАнотація:
Ce travail expérimental s’intéresse à l’écoulement en aval d’un swirler statique court. L’induction d’un mouvement de swirl est une solution connue pour augmenter le gradient pariétal de vitesse. L’augmentation du frottement pariétal présente un intérêt industriel dans les échangeurs de chaleur pour accroître leurs potentiels de transfert de chaleur et diminuer leurs vitesses d’encrassement. Nous proposons d’approfondir la connaissance des écoulements avec swirl décroissant à faibles nombres de Reynolds pour lesquels l’intérêt énergétique est a priori plus important. Dans un premier temps, le champ d’écoulement est caractérisé à l’aide de méthodes optiques, pour identifier le type de tourbillon caractérisant le swirl. Dans un second temps, la méthode électrochimique est utilisée pour mesurer le frottement pariétal instationnaire. Par analogie, ces mesures permettent d’obtenir une première estimation du transfert de chaleur en écoulement anisothermeThis experimental work is interested in understanding the flow downstream a short static swirler. Inducing a swirl motion is a known solution to increase the wall velocity gradient. The increase in wall shear stress is useful in industrial heat exchangers in order to enhance their heat transfer capabilities and reduce their fouling rates. We try to go deeper into knowledge of decaying swirl flows, for low Reynolds number for which energy interest is greater a priori. First, we study the flow field with optical methods in order to identify type of vortex characteristics of the swirl. Second, electrochemical method is used to measure the unsteady wall shear stress. By analogy, these measurements give a first estimate of the heat transfer for the case of non-isothermal flows
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Camata, Mauricio Bishop. "Análise da influência de diferentes geometrias de retificador de fluxo no desempenho de um sensor tipo \"impulse swirl meter\" utilizado para medição de cabeçotes." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3149/tde-03032017-114543/.
Повний текст джерелаАнотація:
O número de swirl de um cabeçote de motor de combustão interna pode ser medido pelo método de vazão em regime permanente. Nesse método o ar é forçado através do cabeçote para diferentes aberturas de válvula. O sensor comumente utilizado nas plataformas para a medição do swirl é o do tipo ISM (impulse swirl meter) que utiliza um retificador de fluxo como o componente principal para capturar o momento angular de rotação do fluxo de ar. Esse trabalho visa encontrar as dimensões geométricas para o retificador de fluxo utilizado em sensor tipo ISM, de tal forma que esse retificador possibilite a realização das medições com a menor interferência possível no resultado final. Dezesseis retificadores de diferentes dimensões foram construídos a partir do processo conhecido como prototipagem rápida. Vários ensaios foram realizados em uma plataforma que utiliza o método de vazão em regime permanente para a medição de swirl em cabeçotes. Para todos os ensaios foi utilizando um mesmo cabeçote de motor diesel como gerador de swirl. No capítulo conclusões são apresentadas as dimensões geométricas que resultaram em menor interferência no fluxo e uma maior eficiência do sensor, bem como sugestões para trabalhos futuros.The swirl number of a cylinder head can be measured by a steady state flow method in which air is forced through the cylinder head for different valve openings. The sensors commonly used on the swirl measurement platform are of the ISM type (impulse swirl meter) that use a flow straightener as the main component to capture the rotational angular momentum of the air flow. This study objective is to determine the geometric dimensions for the flow straightener used in the ISM sensor, which still allows the measurement but causes the least interference on the measurement result. Sixteen different flow straighteners were constructed by rapid prototyping process. Several tests were performed on a platform that uses the steady state flow method to measure the swirl number of cylinder heads. For all tests the same cylinder head was used as swirl generator. The conclusion chapter presents the geometric dimensions that caused the least interference in the flow and resulted in a greater sensor efficiency, as well as suggestions for future studies.
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Bompelly, Ravi K. "Lean blowout and its robust sensing in swirl combustors." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47529.
Повний текст джерелаАнотація:
Lean combustion is increasingly employed in both ground-based gas turbines and aircraft engines for minimizing NOx emissions. Operating under lean conditions increases the risk of Lean Blowout (LBO). Thus LBO proximity sensors, combined with appropriate blowout prevention systems, have the potential to improve the performance of engines. In previous studies, atmospheric pressure, swirl flames near LBO have been observed to exhibit partial extinction and re-ignition events called LBO precursors. Detecting these precursor events in optical and acoustic signals with simple non-intrusive sensors provided a measure of LBO proximity.
This thesis examines robust LBO margin sensing approaches, by exploring LBO precursors in the presence of combustion dynamics and for combustor operating conditions that are more representative of practical combustors, i.e., elevated pressure and preheat temperature operation. To this end, two combustors were used: a gas-fueled, atmospheric pressure combustor that exhibits pronounced combustion dynamics under a wide range of lean conditions, and a low NOx emission liquid-fueled lean direct injection (LDI) combustor, operating at elevated pressure and preheat temperature. In the gas-fueled combustor, flame extinction and re-ignition LBO precursor events were observed in the presence of strong combustion dynamics, and were similar to those observed in dynamically stable conditions. However, the signature of the events in the raw optical signals have different characteristics under various operating conditions. Low-pass filtering and a single threshold-based event detection algorithm provided robust precursor sensing, regardless of the type or level of dynamic instability. The same algorithm provides robust event detection in the LDI combustor, which also exhibits low level dynamic oscillations. Compared to the gas-fueled combustor, the LDI events have weaker signatures, much shorter durations, but considerably higher occurrence rates. The disparity in precursor durations is due to a flame mode switch that occurs during precursors in the gas-fueled combustor, which is absent in the LDI combustor.
Acoustic sensing was also investigated in both the combustors. Low-pass filtering is required to reveal a precursor signature under dynamically unstable conditions in the gas-fueled combustor. On the other hand in the LDI combustor, neither the raw signals nor the low-pass filtered signals reveal precursor events. The failure of acoustic sensing is attributed in part to the lower heat release variations, and the similarity in time scales for the precursors and dynamic oscillations in the LDI combustor. In addition, the impact of acoustic reflections from combustor boundaries and transducer placement was addressed by modeling reflections in a one-dimensional combustor geometry with an impedance jump caused by the flame.
Implementing LBO margin sensors in gas turbine engines can potentially improve time response during deceleration transients by allowing lower operating margins. Occurrence of precursor events under transient operating conditions was examined with a statistical approach. For example, the rate at which the fuel-air ratio can be safely reduced might be limited by the requirement that at least one precursor occurs before blowout. The statistics governing the probability of a precursor event occurring during some time interval was shown to be reasonably modeled by Poisson statistics. A method has been developed to select a lower operating margin when LBO proximity sensors are employed, such that the lowered margin case provides a similar reliability in preventing LBO as the standard approach utilizing a more restrictive operating margin. Illustrative improvements in transient response and reliabilities in preventing LBO are presented for a model turbofan engine. In addition, an event-based, active LBO control approach for deceleration transients is also demonstrated in the engine simulation.
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Abdulsada, Mohammed. "Flashback and blowoff characteristics of gas turbine swirl combustor." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/24193/.
Повний текст джерелаАнотація:
Gas turbines are extensively used in combined cycle power systems. These form about 20% of global power generating capacity, normally being fired on natural gas, but this is expected in the future to move towards hydrogen enriched gaseous fuels to reduce CO2 emissions. Gas turbine combined cycles can give electrical power generation efficiencies of up to 60%, with the aim of increasing this to 70% in the next 10 to 15 years, whilst at the same time substantially reducing emissions of contaminants such as NOx. The gas turbine combustor is an essential and critical component here. These are universally stabilized with swirl flows, which give very wide blowoff limits, and with appropriate modification can be adjusted to give very low NOx and other emission. Lean premixed combustion is commonly used at pressures between 15 to 30 bar, these even out hot spots and minimise formation of thermal NOx. Problems arise because improving materials technology/improved cooling techniques allow higher turbine inlet temperatures, hence higher efficiencies, but with the drawback of potentially higher emissions and stability problems. This PhD study has widely investigated and analysed two different kinds of gas turbine swirl burners. The research has included experimental investigation and computational simulation. Mainly, the flashback and blowoff limits have been comprehensively analysed to investigate their effect upon swirl burner operation. The study was extended by using different gas mixtures, including either pure gas or a combination of more than one gas like natural gas, methane, hydrogen and carbon dioxide. The first combustor is a 100 kW tangential swirl combustor made of stainless steel that has been experimentally and theoretically analysed to study and mitigate the effect of flashback phenomena. The use of a central fuel injector, cylindrical confinement and exhaust sleeve are shown to give large benefits in terms of flashback resistance and acts to reduce and sometimes eliminate any coherent structures which may be located along the axis of symmetry. The Critical Boundary Velocity Gradient is used for characterisation of flashback, both via the original Lewis and von Elbe formula and via new analysis using CFD and investigation of boundary layer conditions just in front of the flame front. Conclusions are drawn as to mitigation technologies. It is recognized how isothermal conditions produce strong Precessing Vortex Cores that are fundamental in producing the ii final flow field, whilst the Central Recirculation Zones are dependent on pressure decay ratio inside the combustion chamber. Combustion conditions showed the high similarity between experiments and simulation. Flashback was demonstrated to be a factor highly related to the strength of the Central Recirculation Zone for those cases where a Combustion Induced Vortex Breakdown was allowed to enter the swirl chamber, whilst cases where a bluff body impeded its passage showed a considerable improvement to the resistance of the phenomenon. The use of nozzle constrictions also reduced flashback at high Reynolds number (Re). All these results were intended to contribute to better designs of future combustors. The second piece of work of this PhD research included comprehensive experimental work using a generic swirl burner (with three different blade inserts to give different swirl numbers) and has been used to examine the phenomena of flashback and blowoff in the swirl burner in the context of lean premixed combustion. Cylindrical and conical confinements have been set up and assembled with the original design of the generic swirl combustor. In addition to that, multi-fuel blends used during the experimental work include pure methane, pure hydrogen, hydrogen / methane mixture, carbon dioxide/ methane mixture and coke oven gas. The above investigational analysis has proved the flashback limits decrease when swirl numbers decrease for the fuel blends that contain 30% or less hydrogen. Confinements would improve the flashback limit as well. Blowoff limits improve with a lower swirl number and it is easier to recognise the gradual extinction of the flame under blowoff conditions. The use of exhaust confinement has created a considerable improvement in blowoff. Hydrogen enriched fuels can improve the blowoff limit in terms of increasing heat release, which is higher than heat release with natural gas. However, the confinements complicate the flashback, especially when the fuel contains a high percentage of hydrogen. The flashback propensity of the hydrogen/methane blends becomes quite strong. The most important features in gas turbines is the possibility of using different kinds of fuel. This matter has been discussed extensively in this project. By matching flashback/blowoff limits, it has been found that for fuels containing up to 30% of hydrogen, the designer would be able to switch the same gas turbine combustor to multifuels whilst producing the same power output.
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NOGUEIRA, ANTONIO CARLOS RIBEIRO. "HEAT TRANSFER IN TURBULENT SWIRL FLOW THROUGH RECTANGULAR DUCTS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24953@1.
Повний текст джерелаАнотація:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO presente trabalho investigou numericamente e experimentalmente as características de transferência de calor e queda de pressão de um escoamento espiralado, turbulento, de caindo através de um duto retangular de elevada razão de aspecto. A condição de escoamento espiralado na estrada do duto foi obtida por meio de tubos paralelos contendo fitas torcidas de modo a produzir vórtices girando em sentidos opostos, dois a dois. Coeficientes de transferência de calor locais e médios foram determinados através da utilização da técnica de sublimação de naftaleno em conjunto com a anologia entre processos de transferência de calor e massa. Os valores locais foram medidos sobre toda a superfície ativa do duto, com o auxílio de uma mesa de coordenadas controlada por microcomputador. Resultados para os coeficientes transferência de calor e da queda de pressão foram obtidas para três valores do número de Reynolds do duto e para três valores da intensidade do escoamento espiralado, dados pela utilização de fitas torcidas com diferentes relações de passo/diâmetro. Para posições axiais próximas da entrada do duto, os resultados revelaram altas taxas de aumento na transferência de calor, relativamente ao caso base, representado por escoamento turbulento sem a imposição do escoamento espiralado. Os resultados para a queda de pressão demonstraram que a presença da componente tangencial da velocidade do escoamento espiralado imposto reduziu os efeitos de recuperação de pressão existentes na região de entrada de dutos com entrada abrupta. Foi também verificado que o comprimento de desenvolvimento hidrodinâmico do escoamento aumenta com a intensidade do escoamento espiralado. As equações de conservação de massa , movimento linear e energia, incorporadndo o modelo de turbulência K – E foram resolvidas numericamente para a configuração em estudo. Os resultados numéricos apresentaram boa concordância com os experimentos, permitindo a
The presente work investigated experimentally and numerically the heat transfer and pressure drop characteristics of turbulent decaying swirl flows through a rectangular duct of high aspect ratio. The swirl flow inlet condition was obtained by a set of parallel tubes with twisted-tape inserts wich produced pairs of counterrotating vortices. Local and average heat transfer coefficients were determined by the utilization of the naphthalene sublimation technique in conjunction with the analogy between heat and mass transfer. Local result were obtained along the whole active surface of the duct, utilizing a computer-assisted coordinate table and depth gage. The study encompassed the investigation of the local and average heat transfer coefficient distribution and pressure drop, for three values of the duct Reynolds number, and for three values of the swirl intensity given by different tape pitch-to-diameter rations. The results showed regions of high heat transfer augmentation situated close to the entrance of the duct, when compared to the base case results characterized by turbulent flow through a duct without the swirl flow inlet condition. The pressure drop results demonstrated that the presence of the tangencial velocity component of the imposed swirl flow was seen to reduce the pressure recover effect present in sharp-edged entrance ducts. It was also verifyied that the hydroninamic developing length increases with the intensity of the swirl flow. The equations governing conservation of mass, linear momentum and energy were solved numerically for the configuration investigated. The K-E turbulence model was employed. The numerical results displayed good agreement with the experiments and provided additional information related to velocity and temperature fields which complemented the experimental program.
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Yuan, Ruoyang. "Measurements in swirl-stabilised spray flames at blow-off." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709345.
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Lewis, Paul. "Pre-swirl rotor-stator systems : flow and heat transfer." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516951.
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Oh, David Y. (David Younghee). "The use of swirl to clean nuclear rocket plumes." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/46428.
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Al-Shaghdari, Mohammed A. "The evaluation of time-dependent flow in swirl burners." Thesis, University of South Wales, 1997. https://pure.southwales.ac.uk/en/studentthesis/the-evaluation-of-timedependent-flow-in-swirl-burners(e2caff50-bfda-4bc9-85f4-e91182d53bd7).html.
Повний текст джерелаАнотація:
Swirl burners are widely used in industry. Recent environmental concerns, particularly on emissions from combustion processes, have introduced the requirement to modify these processes to reduce emissions whilst at the same time maintaining combustion efficiency. This thesis presents details of experimental and computational studies into the flowfield structures of swirl burners. Previous investigators have concentrated on the time-average flows, but it has become apparent that these are insufficient to enable pollutant emissions to be accurately predicted. Knowledge of the time-temperature and species history is needed to obtain better predictions. Pivotal to this is a detailed determination of the time-dependent structure of the flow. In this study, series of experiments were carried out at different inlet configurations and conditions. The flowrate and swirl number were varied as well as the injection mode, inlet length and exit geometry. The burner flow was characterised by measuring axial, tangential and radial velocities using a Laser Doppler Anemometer. A Computational Fluid Dynamics modelling package, FLUENT was used to produce two and three-dimensional computational models to predict the flowfield structures of the burners in isothermal and combustion cases. Four turbulence models were evaluated in the prediction: the k-e Model, the Algebraic Stress Model (ASM), the Reynolds Stress Model (RSM) and the Re-normalisation Group Model (RNG). Constant velocity scaling of the 100 and 500 kW burner was examined in both experimental and computational studies. The experimental results show that the flowfield structures in both burners are nonaxisymmetric and develop three-dimensional time-dependent coherent structures in the flow. The experimental results have been compared with the computational model predictions. The comparisons reveal very good agreement between the time average measurement and the predictive values, especially downstream of the burner exit. This work was extended to investigate the following novel phenomena: a). The computational prediction of the flowfield structure was extended to include different inlet boundary conditions with both the RSM and the RNG turbulence models. The model was also extended to investigate the time-dependent flows. b). The influence of varying the inlet and exit geometries and conditions on the flow patterns and the reverse flow zone was examined in detail. A 500 kW swirl burner with scroll inlet was designed and characterized with time-dependent flows to simulate the Precessing Vortex Core. This investigation showed very good agreement with experimental velocity data with less constrained boundary conditions that had previously obtained. The time-dependent simulation was limited by the computer speed and processing capability but identified that such analysis is possible when computer power allows and has the potential to model the flow in greater detail yielding more accurate data on pollution emissions.
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Ganeshalingam, Jeyakumar. "Swirl-induction for improved solid-liquid flow in pipes." Thesis, University of Nottingham, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.655744.
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Spangelo, Øystein. "Experimental and Theoretical Studies of a Low Nox Swirl Burner." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-310.
Повний текст джерелаАнотація:
Nitrogen oxides emitted to the atmosphere can cause health problems for humans and environmental problems such as acid rain and global warming. The main part of the world energy consumption involves combustion; hence nitrogen oxide abatement in combustion is an important research field. Formation and reduction of NOx in combustion and the current regulations on NOx emissions are reviewed.
A novel low NOx swirl stabilized gas burner concept, the Swirl Burner, has been studied experimentally, theoretically and numerically. Flame stabilization, rapid air and fuel mixing and internal flue gas recirculation are provided by a strongly swirling flow generated in this patented burner concept. NOx emissions have been measured below 25 and 45 ppmv dry corrected to 3% O2 in the flue gases using methane and propane as fuel respectively.
Studying the effect of varying geometrical parameters on the emissions of NOx, fuel and air supply pressure and flame stability, have resulted in an optimized burner design. The optimized Swirl Burner has successfully been scaled from a 200 kW burner down to a 20 kW burner and up to a 370 kW burner, using a constant velocity scaling criteria which is the most commonly used scaling criteria for industrial burners. Experiments with the scaled burners have revealed that the fuel to air momentum should be preserved while scaling the burner. The 200 kW and the 370 kW burners were operated stable with the boiler to burner diameter (confinement) ratio in the range 5.3-6.7. The 20 kW burner, which was operated in an un-cooled and a water-cooled combustion chamber with confinement ratio of 8.1, was found to have a narrower range of stable operation with regards to thermal throughput. High post-flame heat extraction, which is enhanced by increased confinement ratio and combustion chamber cooling, reduces the emissions of NOx, but might cause flame instabilities.
NOx emissions measured from the three Swirl Burners scale well with NOx scaling correlations based on flame volume as a leading-order parameter for NOx formation (Weber, 1996). The correlations consider the effect of heat extraction on flame volume and emissions of NOx. These correlations indicate that the heat extraction from the 20 kW burner is increasing with increasing thermal throughput. The 200 kW and the 370 kW burners were, from the correlations, found to operate with constant heat extraction.
Flame volume and shape are studied by non-intrusive measurements of OH radicals with the 20 kW burner using laser induced fluorescence. The measurements show that the flame volume is reduced with increasing thermal throughput. Measurements of NOx from this burner also show a reduction with increasing thermal throughput. These results support the theoretical considerations of the flame volume as being the leading-order parameter for NOx formation.
An evaluation of turbulence models and combustion models suitable for studying the Swirl Burner by computational fluid dynamics has been carried out. For this evaluation, a 2D computational model of the 20 kW burner has been used. For closure of the Reynolds Averaged Navier-Stokes equations for turbulent flow, three models have been evaluated.
These are the standard k-ε model, the RNG k-ε model and the Reynolds Stress model.
Also for modelling of combustion, three models have been evaluated, namely the Eddy Dissipation model, the Equilibrium PDF model and the Flamelet PDF model. For studying the Swirl Burner, a combination of the Reynolds Stress model and the Flamelet PDF model were found to be most suitable for modelling of turbulence and combustion respectively.
Computational results with the 20 kW burner indicate that flue gases are recirculated into a central toroidal recirculation zone downstream the burner exit. The computations are further compared with the OH concentrations measured with laser induced fluorescence.
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Colby, Jonathan A. "Flow Field Measurements in a Counter-Swirl Stabilized Liquid Combustor." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10470.
Повний текст джерелаАнотація:
To adhere to the current requirements for NOx and CO emissions in combustion systems, modern land and air based gas turbine engines often operate in the fuel lean regime. While operating near the lean blow out (LBO) limit does reduce some harmful emissions, combustor stability is sacrificed and extinction becomes a major concern. To fully understand the characteristics of lean operation, an experimental study was conducted to map the time averaged flow field in a typical industrial, counter-swirling, liquid fuel combustor. This study examined two steady-state operating conditions, both near the lean extinction limit for this swirl burner. Using an LDV/PDPA system, 2-D mean and fluctuating velocities, as well as Reynolds stresses, were measured throughout the combustor. These measurements were taken for both the non-reacting and reacting flow fields, enabling a direct analysis of the result of heat addition and increased load on a turbulent swirling flow field. To further understand the overall flow field, liquid droplet diameter measurements were taken to determine the fuel spray characteristics as a function of operating pressure and rated spray angle. Chemical composition at the combustor exit was also measured, with an emphasis on the concentrations of both CO and NOx emissions. This large database of aerodynamic and droplet measurements improves understanding of the swirling, reacting flow field and aids in the accurate prediction of lean blow-out events. With this understanding of the lean blow-out limit, increased fuel efficiency and decreased pollutant emissions can be achieved in industrial combustors, especially those used for thrust in the airline industry.
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O'Connor, Jacqueline. "Response of a swirl-stabilized flame to transverse acoustic excitation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43756.
Повний текст джерелаАнотація:
This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. A description of the velocity-coupled transverse instability mechanism is explained with companion measurements describing each of the velocity disturbance pathways. Dependence on acoustic frequency, amplitude, and field symmetry is discussed. Significant emphasis is placed on the response of a swirling flow field to a transverse acoustic field. Details of the dynamics of the vortex breakdown bubble and the shear layers are explained using a wide variety of measurements for both non-reacting and reacting flow cases. This thesis concludes with an overview of the impact of this work and suggestions for future research in this area.
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Sakajo, Takashi. "Numerical Computation of three-dimensional vortex sheet with swirl flow." 京都大学 (Kyoto University), 1999. http://hdl.handle.net/2433/181452.
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Babbedge, Thomas Sebastian Reed. "Photometric redshifts and luminosity functions from the SWITZER SWIRE survey." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415162.
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Sheen, Dong-Hyon. "Swirl-stabilised turbulent spray flames in an axisymmetric model combustor." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445249.
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Novotny, Pavel [Verfasser], and Bernhard [Akademischer Betreuer] Weigand. "Stability of swirl tube flow / Pavel Novotny ; Betreuer: Bernhard Weigand." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1201646375/34.
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Salcedo, Saulo Alfredo Gómez. "CFD analysis in spray combustion using a pressure swirl injector." Instituto Tecnológico de Aeronáutica, 2015. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=3292.
Повний текст джерелаАнотація:
The object of this work is to apply CFD simulation in the description of the spray burning. As a case study, a pressure swirl injector, characterized and tested by NIST, has been chosen, which atomize liquid kerosene in an atmosphere of gaseous oxygen. The chamber dimensions allow a complete evaporation, avoiding the impact of drops on the circular wall. Swirl-axisymmetric domain and steady state permit to include combustion, a complex process, without requiring of high computational resources. Continuous phase is treated with an Eulerian reference, while fuel drops are tracked following the Lagrangian formulation. Chemical kinetics is reduced to the concept of mixture fraction. This assumption avoids the solution of too many transport equations for all involved species. In the first simulation, the inlet boundary of the continuous phase is obtained from the numerical solution of a fully developed flow transporting the oxidant gas. Then, four cases are proposed and solved, changing the turbulence intensity and swirl velocity on the inlet boundary, each parameter with two different values. Finally, results for the axial velocity, streamlines, drops trajectories, temperature, distribution and total production of selected species are analyzed and compared with other related studies.
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Guimaraes, Bucalo Tamara. "Fluid Dynamics of Inlet Swirl Distortions for Turbofan Engine Research." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82921.
Повний текст джерелаАнотація:
Significant effort in the current technological development of aircraft is aimed at improving engine efficiency, while reducing fuel burn, emissions, and noise levels. One way to achieve these is to better integrate airframe and propulsion system. Tighter integration, however, may also cause adverse effects to the flow entering the engines, such as total pressure, total temperature, and swirl distortions. Swirl distortions are angular non-uniformities in the flow that may alter the functioning of specific components of the turbomachinery systems. To investigate the physics involved in the ingestion of swirl, pre-determined swirl distortion profiles were generated through the StreamVane method in a low-speed wind tunnel and in a full-scale turbofan research engine. Stereoscopic particle image velocimetry (PIV) was used to collect three-component velocity fields at discrete planes downstream of the generation of the distortions with two main objectives in mind: identifying the physics behind the axial development of the distorted flow; and describing the generation of the distortion by the StreamVane and its impact to the flow as a distortion generating device.
Analyses of the mean velocity, velocity gradients, and Reynolds stress tensor components in these flows provided significant insight into the driving physics. Comparisons between small-scale and full-scale results showed that swirl distortions are Mach number independent in the subsonic regime. Reynolds number independence was also verified for the studied cases. The mean secondary flow and flow angle profiles demonstrated that the axial development of swirl distortions is highly driven by two-dimensional vortex dynamics, when the flow is isolated from fan effects. As the engine fan is approached, the vortices are axially stretched and stabilized by the acceleration of the flow. The flow is highly turbulent immediately downstream of the StreamVane due to the presence of the device, but that vane-induced turbulence mixes with axial distance, so that the device effects are attenuated for distances greater than a diameter downstream, which is further confirmed by the turbulent length scales of the flow. These results provide valuable insight into the generation and development of swirl distortion for ground-testing environments, and establishes PIV as a robust tool for engine inlet investigations.Ph. D.
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Frohnapfel, Dustin Joseph. "Experimental Investigation of Fan Rotor Response to Inlet Swirl Distortion." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71323.
Повний текст джерелаАнотація:
Next generation aircraft design focuses on highly integrated airframe/engine architectures that exploit advantages in system level efficiency and performance. One such design concept incorporates boundary layer ingestion which locates the turbofan engine inlet near enough to the lifting surface of the aircraft skin that the boundary layer is ingested and reenergized. This process reduces overall aircraft drag and associated required thrust, resulting in fuel savings and decreased emissions; however, boundary layer ingestion also creates unique challenges for the turbofan engines operating in less than optimal inlet flow conditions.
The engine inlet flow profiles predicted from boundary layer ingesting aircraft architectures contain complex distortions that affect the engine operability, durability, efficiency, and performance. One component of these complex distortion profiles is off-axial secondary flow, commonly referred to as swirl. As a means to investigate the interactions of swirl distortion with turbofan engines, an experiment was designed to measure distorted flow profiles in an operating turbofan research engine.
Three-dimensional flow properties were measured at discrete planes immediately upstream and immediately downstream of the fan rotor, isolating the component for analysis. Constant speed tests were conducted under clean and distorted test conditions. For clean tests, a straight cylindrical inlet duct was attached to the fan case; for distorted tests, a StreamVane swirl distortion generator was inserted into the inlet duct. The StreamVane was designed to induce a swirl distortion matching results of computation fluid dynamics models of a conceptual blended wing body aircraft at a plane upstream of the fan. The swirl distortion was then free to develop naturally within the inlet duct before being ingested by the engine.
Results from the investigation revealed that the generated swirl profile developed, mixed, and dissipated in the inlet duct upstream of the fan. Measurements immediately upstream of the fan rotor leading edge revealed 50% reduction in measured flow angle magnitudes along with evidence of fanwise vortex convection when compared to the StreamVane design profile. The upstream measurements also indicated large amounts of secondary flow entered the fan rotor. Measurements immediately downstream of the fan rotor trailing edge demonstrated that the fan processed the distortion and further reduced the intensity of the swirl; however, non-uniform secondary flow persisted at this plane. The downstream measurements confirmed that off-design conditions entered the fan exit guide vanes, likely contributing to cascading performance deficiencies in downstream components and reducing the performance of the propulsor system.Master of Science
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MA, ZHANHUA. "INVESTIGATION ON THE INTERNAL FLOW CHARACTERISTICS OF PRESSURE-SWIRL ATOMIZERS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1016634882.
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LI, GUOQIANG. "EMISSIONS, COMBUSTION DYNAMICS, AND CONTROL OF A MULTIPLE SWIRL COMBUSTOR." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092767684.
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Mohamed, Jainulabdeen Mohammed Abdul Kadher. "Combustion Noise and Instabilities from Confined Non-premixed Swirl Flames." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1560867354695989.
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Burkhalter, Matthew W. "Atomization and mixing performance of swirl-venturi lean direct injection." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1433.
Повний текст джерелаАнотація:
This paper investigated the effects of swirl number and momentum ratio on the atomization and mixing performance of Swirl-Venturi Lean Direct Injection technology. Mie scattering of liquid water, was used to identify the location of water droplets in a cross section of the injector spray. Experiments were performed with three air swirlers with vane angles of 45, 52 and 60 degrees. The swirl number varied from 0.58 to 1.0 and air-to-liquid ratios from 15.8 to 35.6. A transition was observed in the liquid spray distribution for the 52 degree case, which unexpectedly produced twice as much signal than the 45 and 60 degree cases. The main cause of this increased signal may be due to instabilities in the flow when transitioning from low to high swirl states. The results from investigation of swirl number it was found that the spray pattern for is sensitive to swirl intensity. Two flow states were observed for a lower and higher swirl flow as well as a transition state that occurred with the lower swirl state. This work may aid in the specific inquiry of physical mechanisms relating to the effect of flow states on spray distribution. It is found that improved atomization and mixing performance are a result of increase in swirl number.
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Dawson, Dylan Paul. "Design and Low-Speed Validation of a Tailored Low-Loss Flow Straightening Device." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/97888.
Повний текст джерелаАнотація:
In many applications, non-uniform flows are undesirable and have a negative system impact. Non-uniform flows can arise in many ways such as in geometry changes and turns in piping/ducting, as well as with lip separation in certain aircraft engine inlets at high angle of attack. These non-uniformities can come with a variety of secondary flow patterns and thus highly three-dimensional flow. In a cylindrical coordinate system, these secondary (or in-plane) velocities have tangential and radial components. The tangential velocity is typically referred to as swirl and is the component of secondary flow that has the most system impact. These systems include industrial compressors, aircraft engines, and flow metering devices.
In industrial compressors and aircraft engines, swirl translates into off-design incidence angles on the blades. The off-design incidence can lead to blade stall, losses in performance, and loss in system operability. In flow metering, swirl can significantly reduce measurement accuracy, and is regulated in industries such as the oil and gas industry.
In the straightening of low-speed flows with approximately constant density and axial velocity, the velocity magnitude decreases and pressure increases along streamlines. This creates an unfavorable streamwise pressure gradient that inhibits the fluids ability to remain attached to the convex suction surface of the turning vane. This suction side separation causes the flow to under turn and exit at an angle not equal to the vane's trailing edge angle. The angle measured between the vane's trailing edge and the actual exiting flow angle is referred to as the deviation. Research on specific airfoil shaped turning vanes set up in linear cascade arrangements provides experimental data detailing the deviation measured at ranges of inlet flow conditions and vane spacing. These experimental data sets indicate that deviation angles were measured to be 10 degrees or higher in large vane spacing, high design flow turning arrangements. It is evident that in order to effectively straighten flow with turning vanes, the deviation must be predicted and accounted for in the design stage.
In this work, the design system of a new method of swirl mitigation is detailed and experimentally validated in a low-speed wind tunnel. The design system builds upon the fundamentals of the swirl-producing StreamVane design methods and is thus designated as the Inverse StreamVane. The complex arrangement of turning vanes in the StreamVane and Inverse StreamVane alike creates a spanwise variation of vane spacing. Calculated by a proximity approximation method, this local vane spacing, along with the local inlet flow conditions, become inputs to a derived function that predicts the local flow deviation. A root-finding method is utilized at each incremental vane section of each turning vane to converge on the design cambers that set the predicted local deviation angles equal to the local trailing edge angles.
Experimental and computational results validate the design method employed with the reduction of an experimentally measured 30 degree peak paired swirl profile to a 3 degree peak, 1.01 degree rms, swirl profile. Flow angularity and loss measurements detailed at 1/2 duct diameter downstream of the 1/6 duct diameter axial length of the device introduce the Inverse StreamVane as a very effective and efficient method of swirl mitigation.MS