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1
Hall, Oskar. "The flow between two coaxial cones." Thesis, University of Exeter, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486775.
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This thesis provides a study of the flow between two coaxial cones, a geometry with many interesting features and of practical importance. We consider the flow for different driving mechanisms and start by studying the highly viscous flow when the fluid is driven by rotation of the cones or a spherical lid. The solution is found through a low Reynolds number e)...pansion expressed as a combination of forced modes and geometric eigenmodes. The latter may cause an infinite sequence of counter-rotating vortices at the apex of the cones, we study the flow topology for a wide range of parameter values and specify when an infinite sequence of eddies occurs. We also cons.ider the non-axisymmetric Stokes flow where each wave number m gives rise to infinitely many eigeninodes. We map the spectra for different wave numbers and study the relative dominance between the eigenmodes. In contrast to the axisymmetric flow and the flow in one cone, no infinite sequence of eddies occur except in special cases. The solutions to the Stokes equations can be expressed as a symmetric and anti-symmetric part and we consider the response from a moving nonrigid lid, where the .flow exhibits a transition from a flow with closed streamlines to what appears to be a completely chaotic flow. in the second part we consider the flow which results from a point sink situated at the apex of the cones. The problem is reminiscent of the classical Jeffery-Hamel flow. We study the flow in the Stokes limit and find that the similarity solution experiences a break-down for certain cone openings. For a general Reynolds number the governing equations do not admit separable solutions so we consider asymptotic expansions of the flow in a narrow gap limit. In the far field the viscous forces dominate and the flow assumes a parabolic profile, the influence of inertia increases as we move downstream and by computing solutions of a PDE we find the resulting boundary layer flow. In the final chapter we consider the same flow for a slightly different cone geometry where there is a constant gap between the cones. We compare the solutions between the two geometries and discuss their qualitative differences.
2
Lin, Jehnming. "Characterisation of coaxial laser cladding." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367284.
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Hall, Philip D. "Design of a coaxial split flow pulse detonation engine." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FHall.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2006.Thesis Advisor(s): Jose O. Sinibaldi, Christopher M. Brophy. "June 2006." Includes bibliographical references (p. 41-42). Also available in print.
4
Segalini, Antonio <1983>. "Experimental analysis of coaxial jets: instability, flow and mixing characterization." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2474/.
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The velocity and mixing field of two turbulent jets configurations have been experimentally characterized by means of cold- and hot-wire anemometry in order to investigate the effects of the initial conditions on the flow development.
In particular, experiments have been focused on the effect of the separation wall between the two streams on the flow field.
The results of the experiments have pointed out that the wake behind a thick wall separating wall has a strong influence on the flow field evolution. For instance, for
nearly unitary velocity ratios, a clear vortex shedding from the wall is observable. This phenomenon enhances the mixing between the inner and outer shear layer. This enhancement in the fluctuating activity is a consequence of a local absolute instability of the flow which, for a small range of velocity ratios, behaves as an hydrodynamic oscillator with no sensibility to external perturbations. It has been suggested indeed that this absolute
instability can be used as a passive method to control the flow evolution.
Finally, acoustic excitation has been applied to the near field in order to verify whether or not the observed vortex shedding behind the separating wall is due to a global oscillating mode as predicted by the theory.
A new scaling relationship has been also proposed to determine the preferred frequency for nearly unitary velocity ratios. The proposed law takes into account both the Reynolds number and the velocity ratio dependence of this frequency and, therefore, improves all the previously
proposed relationships.
5
Tian, Bin. "Dynamics and stability of pinned-clamped coaxial cyclindrical shells conveying viscous flow." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69739.
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This thesis presents a theoretical study of the stability of pinned-clamped and clamped-pinned coaxial cylindrical shells conveying internal and/or annular incompressible viscous fluid flow.In the present analytical model, fluid viscous effects are taken into consideration. Generally, the viscous nature of the fluid results in both steady and unsteady viscosity-related loads being exerted on the shells, the latter of which are approximated by their inviscid counterpart in this thesis. Upstream pressurization of the flow (to overcome frictional pressure drop) and skin friction on the shell surfaces are taken into account, generating time-averaged normal and tangential loads on the shells. In this model, the shell motions are described by Flugge's shell equations, suitably modified to incorporate the time-averaged stress resultants arising from viscous effects. The unsteady fluid-dynamic forces in these equations are formulated from potential flow theory: the perturbation pressures on the shells are determined from the perturbation velocity potentials via the unsteady Bernoulli equation; those velocity potentials are governed by the Laplace equation, which is solved by the Fourier transform technique.
For the clamped-pinned system, since the downstream end of the shell is simply supported, a so-called out-flow model is utilized in modelling the decay of flow perturbations beyond the pinned end.
Comparison is made with the existing results for clamped-clamped and clamped-free cases.
Finally, future work is suggested with regard to setting up a new analytical model with the unsteady viscous effects taken into account.
6
Gautam, Vivek. "Flow and atomization characteristics of cryogenic fluid from a coaxial rocket injector." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7719.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
7
Luu, Van Chi. "Numerical study of the reactive flow in a two-stream, coaxial-jet, axisymmetric bluff-body combustor." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39617.
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Cessou, Armelle. "Stabilisation de la combustion diphasique turbulente au-dessus d'un injecteur coaxial méthanol/air." Rouen, 1994. http://www.theses.fr/1994ROUES039.
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La stabilisation de la combustion diphasique en aval d'un injecteur méthanol/air a été étudiée. L'interférométrie phase Doppler a fourni les champs de vitesse des gouttes analysées par classe de taille. Des images bidimensionnelles des zones de réaction ont été réalisées par fluorescence induite par laser du radical OH. Les niveaux de gris de ces images ont été étalonnées en concentration absolue de OH, et la position de la stabilisation de la flamme a été mesurée. La stabilisation des flammes turbulentes non-prémélangées peut être modélisée à partir du mélange turbulent à grande échelle. La comparaison des champs de vitesse dans le spray et des localisations de la stabilisation de la flamme a montré que ce résultat peut être étendu à la combustion diphasique. L'analyse des fluctuations de vitesse des gouttes en fonction de leur nombre de Stokes a montré le comportement dynamique bimodal du spray dans la zone où la flamme se stabilise. Ne considérant que le fluide à faible nombre de Stokes, la combustion a été analysée dans le référentiel de la fraction de mélange. L'accent a été mis sur le régime dit de vaporisation où les flammes se stabilisent selon deux zones réactives nettement séparées. Deux limites à ce régime apparaissent, une limite inférieure due à la mauvaise qualité de l'atomisation et une limite supérieure dynamique quand le temps de mélange à grande échelle devient trop rapide. La comparaison aux résultats expérimentaux montre que cette analyse décrit correctement le phénomène de stabilisation
9
Rejent, Andrew. "Experimental Study of the Flow and Acoustic Characteristics of a High-Bypass Coaxial Nozzle with Pylon Bifurcations." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250272655.
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10
Davis, Staci Ann. "The manipulation of large- and small-scale flow structures in single and coaxial jets using synthetic jet actuators." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17313.
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Silas, Kevin Alexander. "Phase Transform Time Delay Estimation to Counteract Spectral Haystacking Effects in Jet Exhaust Flow Measurements." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104892.
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This study determined a superior data processing technique for correlating an acoustic signal passing through a subsonic jet engine exhaust in order to estimate the traversal time of the signal. Thrust measurement is possible with enough time delay estimates across different portions of the exhaust. This preliminary study did not take the full array of data necessary to measure thrust, but did validate key aspects of the measurement process. The turbulent shear layers of the exhaust spectrally broaden the signal, creating the appearance of spectral "haystacks", making traditional correlation methods unworkable. An experiment was performed to evaluate the ability of a novel sound source to produce a signal from which a reliable and precise time delay estimate could be found. The test apparatus was installed on either side of a Honeywell TFE731-2 turbofan research engine exhaust cone, with the source and receivers placed near the jet exit plane. The signal was then directed across the jet exhaust. This flow environment is considered an extreme challenge for accurate acoustic signal propagation. A key contribution of this paper is the determination that the Phase Transform processor of the Generalized Cross-Correlation (GCC) method produces the most reliable time delay estimates, for the given signal and flow conditions. Several alternative time delay estimators and GCC processors were examined and evaluated on this data. A proposed explanation is provided for why this time delay estimation technique produces the most accurate results, as well as explanations for why the technique became less reliable as the flow environment became more challenging, with an observed 22% anomalous TDE selection rate for the N1Corr = 60% and N1Corr = 70% conditions combined, versus only 6% for the idle and N1Corr = 50% conditions combined. This paper also details the development and first use of a novel acoustic source that produces a two-tone narrowband signal emanating from a single point – the dual Hartmann generator.Master of Science
This study builds on a Computational Tomography (CT) technique that uses an acoustic signal and an array of receivers to measure the velocity and temperature of a gas flow field. In particular, the velocity and temperature field tested involves multiple turbulent and disruptive elements, requiring a loud and specifically designed signal. As such, a novel acoustic signal generator, the dual Hartmann generator, was designed that is both loud and produces a specific two-toned signal. The key contribution of the study was to process the data, comparing the sets of transmitted and received signals, in order to estimate the time delay amongst receiver pairs – a key input in the CT method. Traditional cross-correlation methods were inadequate, and multiple alternatives were evaluated. The Phase Transform (PHAT) technique showed the most promise, and an explanation is given for why this technique is most suitable for this type of signal.
12
Rhouzlane, Saïd. "Rheologie des mixtures solide-liquide : conception et realisation d'un viscosimetre rotatif a entre fer large." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13079.
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On travaille avec un entrefer large pour avoir un ecoulement aux fortes concentrations, minimiser les interactions des particules avec la paroi et ainsi eviter la perturbation de l'ecoulement. L'approximation de constance du gradient de vitesse ne pouvant etre maintenue dans cet entrefer large on adapte un systeme d'anemometrie laser et on rend homogene l'indice de refraction du couple liquide-solide afin d'exploiter les vitesse dans l'entrefer
13
Fier, Jeffrey Michael Keller Herbert Bishop Keller Herbert Bishop. "Part I. Fold continuation and the flow between rotating, coaxial disks. : Part II. Equilibrium chaos. Part III. A mesh selection algorithm for two-point boundary value problems /." Diss., Pasadena, Calif. : California Institute of Technology, 1985. http://resolver.caltech.edu/CaltechETD:etd-03262008-150456.
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Odier, Nicolas. "Simulation numérique de jets liquides cisaillés par une phase rapide : dynamique de battement à grande échelle et intéraction avec les structures tourbillonnaires." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI068/document.
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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'injectionFuel 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
15
Camano, Schettini Edith Beatriz. "Étude expérimentale des jets coaxiaux avec différences de densité." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0066.
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Les jets coaxiaux ont plusieurs applications pratiques, principalement dans le domaine de la combustion, et particulierement pour les injecteurs de moteurs de fusees, ou l'oxygene liquide (lourd et a faible vitesse) est injecte dans la buse centrale, et l'hydrogene gazeux (tres leger et tres rapide) est injecte dans la buse annulaire. Afin de nous rapprocher de ce type d'ecoulement, nous avons mene des recherches sur les jets coaxiaux, monophasiques, isothermes, avec fortes differences de densite. Les gaz utilises ont ete de l'air, de l'helium et du sf#6. Nous avons mis au point une instrumentation adaptee aux ecoulements heterogenes, basee sur la thermo-anemometrie. Une sonde dite de sillage nous a permis d'identifier les regions de recirculation. Les champs de densite ont ete obtenus avec une sonde de type aspirante. Les parametres les plus importants, pour ce type de jet, sont le rapport de vitesse, r#v, et le rapport de densite, s, qui ont ete regroupes dans le rapport des flux de quantite de mouvement, m. Les jets coaxiaux presentent deux regimes d'ecoulements bien definis: l'un recirculant et l'autre de cone potentiel, qui peuvent etre distingues a partir d'une valeur critique de ce parametre, m#c, pour chaque couple de gaz. M#c vaut 40 a 50 pour l'ensemble des gaz utilises, sauf pour le couple helium-sf#6, pour laquelle m#c 80 - 100. Une bulle de recirculation se developpe avec une frontiere aval pratiquement independante de m (0,9 a 1,2 d#i suivant les differents cas etudies) et une frontiere amont qui remonte vers la buse lorsque m augmente. Les resultats concernant la longueur du cone potentiel se regroupent assez bien en fonction de m, mais il subsiste une legere influence de la densite ; un raccourcissement est constate lorsque le gaz injecte dans la buse annulaire est plus leger que le gaz du jet central. Contrairement a la tendance prevue, le couple helium-sf#6 donne un entrainement plus faible que pour les autres gaz
16
Rehab, Hichem. "Structure de l'écoulement et mélange dans le champ proche des jets coaxiaux." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10074.
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Le present travail est une etude experimentale de l'ecoulement dans le champ proche des jets coaxiaux a fort rapport des vitesses initiales entre le courant annulaire et central. Les objectifs de l'etude sont de clarifier les mecanismes physiques qui gouvernent la dynamique de l'ecoulement et les regimes d'ecoulement. Deux regimes d'ecoulement sont identifies selon les valeurs du rapport des vitesses initiales comparee a une certaine valeur critique. Le premier regime est caracterise par un cone potentiel central dont la longueur est inversement proportionnelle au rapport des vitesses. Un modele d'entrainement base sur la conservation de la masse et le taux d'entrainement turbulent a travers les couches de melange permet d'expliquer et de predire la longueur du cone potentiel central. Le rapport des vitesses initiales represente le parametre cle de l'ecoulement. Au dela d'une valeur critique du rapport des vitesses, le cone potentiel central se brise et un ecoulement de recirculation s'installe. La bulle de recirculation qui se forme a un mouvement de precession a basse frequence et de large amplitude comparee au mode de jet. Le regime de recirculation favorise un melange precoce a la sortie des injecteurs par rapport au regime non recirculant. Les etapes de l'etablissement de la structure fine du melange dans ces jets sont analysees a l'aide d'un scalaire passif a gran nombre de schmidt. On distingue une etape de declenchement des instabilites de cisaillement, puis un processus de reduction des longueurs a etirement constant jusqu'aux echelles diffusionnelles. Le temps necessaire pour atteindre ces echelles depend du nombre de schmidt, et sa valeur elevee induit une pente anormale (-1) sur le spectre des fluctuations de concentration dans la gamme des echelles inertielles.
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Marchand, Olivier. "Sur l'écoulement entre deux disques." Aix-Marseille 2, 1986. http://www.theses.fr/1986AIX22033.
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Etude numerique et experimentale de l'ecoulement entre un disque fixe et un disque en rotation. Les experiences sont realisees en regime laminaire et turbulent par anemometrie a film chaud et visualisations
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Peker, Ekim Atilla. "Momentum Exchange In Coaxial Jet Flows." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606801/index.pdf.
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Coaxial jet flows have a considerable practical application area as water jet pumps. Efficiency of such systems is affected by complex turbulence mechanisms and large-scale vortex structures formed in the mixing regions. An experimental setup is constructed to estimate the momentum exchange rates and mixing of the two jet flows from the coaxial pipes. Pressure distributions along the mixing pipe wall are measured for different flow ratios of the jets. In addition to present experiments, numerical data of two experimental studies from the literature are considered as test cases. Numerical solutions for the test cases are obtained using FLUENT. Experimental and numerical results are compared and adequacy of FLUENT solution is illustrated.
19
Taylor, Mark Victor. "Acoustic and instability properties of coaxial jet flows." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238545.
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Masquelet, Matthieu Marc. "Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47522.
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The understanding and prediction of transient phenomena inside Liquid Rocket Engines
(LREs) have been very difficult because of the many challenges posed by the
conditions inside the combustion chamber. This is especially true for injectors involving
liquid oxygen LOX and gaseous hydrogen GH₂. A wide range of length scales
needs to be captured from high-pressure flame thicknesses of a few microns to the length
of the chamber of the order of a meter. A wide range of time scales needs to be captured,
again from the very small timescales involved in hydrogen chemistry to low-frequency
longitudinal acoustics in the chamber. A wide range of densities needs to be captured,
from the cryogenic liquid oxygen to the very hot and light combustion products. A wide
range of flow speeds needs to be captured, from the incompressible liquid oxygen jet to
the supersonic nozzle. Whether one desires to study these issues numerically or
experimentally, they combine to make simulations and measurements very difficult whereas
reliable and accurate data are required to understand the complex physics at stake. This
thesis focuses on the numerical simulations of flows relevant to LRE applications
using Large Eddy Simulations (LES). It identifies the required features to tackle
such complex flows, implements and develops state-of-the-art solutions
and apply them to a variety of increasingly difficult problems.
More precisely, a multi-species real gas framework is developed inside a conservative,
compressible solver that uses a state-of-the-art hybrid scheme to capture at the same time
the large density gradients and the turbulent structures that can be found in a
high-pressure liquid rocket engine.
Particular care is applied to the
implementation of the real gas framework with detailed derivations of thermodynamic
properties, a modular implementation of select equations of state in the solver.
and a new efficient iterative method.
Several verification cases are performed to evaluate this implementation and the
conservative properties of the solver. It is then validated against laboratory-scaled
flows relevant to rocket engines, from a gas-gas reacting injector to a liquid-gas
injector under non-reacting and reacting conditions. All the injectors considered contain
a single shear coaxial element and the reacting cases only deal with H₂-O₂ systems.
A gaseous oyxgen-gaseous hydrogen (GOX-GH₂) shear coaxial injector, typical
of a staged combustion engine, is first investigated. Available experimental data is
limited to the wall heat flux but extensive comparisons are conducted between
three-dimensional and axisymmetric solutions generated by this solver as well as by other
state-of-the-art solvers through a NASA validation campaign. It is found that the unsteady
and three-dimensional character of LES is critical in capturing physical flow features,
even on a relatively coarse grid and using a 7-step mechanism instead of a 21-step
mechanism. The predictions of the wall heat flux, the only available data, are not very good and
highlight the importance of grid resolution and near-wall models for LES.
To perform more quantitative comparisons, a new experimental setup is investigated under
both non-reacting and reacting conditions. The main difference with the previous setup,
and in fact with most of the other laboratory rigs from the literature, is the presence of
a strong co-flow to mimic the surrounding flow of other injecting elements. For the
non-reacting case, agreement with the experimental high-speed visualization is very good,
both qualitatively and quantitatively but for the reacting case, only poor agreement is
obtained, with the numerical flame significantly shorter than the observed one. In both
cases, the role of the co-flow and inlet conditions are investigated and highlighted.
A validated LES solver should be able to go beyond some experimental
constraints and help define the
next direction of investigation. For the non-reacting case, a new scaling law is suggested after a
review of the existing literature and a new numerical experiment agrees with the
prediction of this scaling law.
A slightly modified version of this non-reacting setup is
also used to investigate and validate the Linear-Eddy Model (LEM), an advanced sub-grid closure
model, in real gas flows for the first time.
Finally, the structure of the trans-critical
flame observed in the reacting case hints at the need for such more advanced
turbulent combustion model for this class of flow.
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Yoshida, Hiroaki. "Studies on gas flows between two coaxial circular cylinders on the basis of kinetic theory." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136189.
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Xu, Hongyi. "Large eddy simulation of turbulent flows in square and annular ducts and confined square coaxial jet." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/NQ27860.pdf.
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Srinivasan, Shriram. "Study of shear-driven unsteady flows of a fluid with a pressure dependent viscosity." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3201.
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Handa, Masato. "Studies on the Bifurcation of Flows between Two Coaxial Circular Cylinders on the Basis of Kinetic Theory of Gases." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147648.
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Nguyen, Vinhson Ba. "Theoretical and experimental study of the stability of clamped-free coaxial cylindrical shells subjected to internal and annular flows of viscous liquid." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39326.
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This thesis presents a theoretical and experimental study of the stability of cantilevered coaxial cylindrical shells conveying incompressible, viscous fluid inside the inner shell and/or in the annulus between the two shells. Two analytical models are developed with experimental verification.In the first model, fluid viscous effects are partially taken into consideration. Both shells are generally considered flexible. Shell motions are described by Flugge's shell equations, modified to take into account the steady viscous loads--flow pressurization and skin friction--acting on the shells. These equations are solved by means of the extended Galerkin method, in which the shell equations and the free-end boundary conditions can be satisfied simultaneously. The unsteady viscous forces are approximated by their inviscid counterparts, the formulation of which is based on linearized potential-flow theory with the assumption that the fluid is inviscid. The solution for these forces is obtained with the Fourier-transform technique; in connection with this technique, different so-called out-flow models are examined, concerning the effect of the downstream flow perturbations on the dynamics of the system.
The second analytical model, on the other hand, fully accounts for the viscous effects of the flow. Here, only the inner shell is flexible, while the outer shell is replaced by an identical rigid cylinder. Shell motions are also described by Flugge's modified shell equations, which incorporate the steady viscous loads exerted on the shell. These equations are solved numerically with the finite-difference method. The unsteady viscous forces are evaluated from flow perturbations which are the solution of the linearized, unsteady Navier-Stokes equations subject to the divergence-free constraint on the flow velocity perturbation. A recently developed, time-marching finite-difference method using "artificial compressibility" is applied to solve the Navier-Stokes equations; for the problem under consideration, this method employs the pressure and velocity perturbations as the dependent flow variables on a staggered grid.
In the experimental part of the thesis, tests involving either annular or inner flow are conducted on cantilevered silicone rubber shells concentrically located within rigid plexiglas cylinders. Measurements are made of (i) the critical flow velocity of the system for various lengths of the shell and annular widths, and (ii) the dominant frequencies of oscillation of the shell for certain selected cases. Both divergence- and flutter-type instabilities are observed.
Comparisons between analytical results and test measurements show that the agreement between experiment and the two proposed analytical models is generally good, both qualitatively and quantitatively, in terms of the overall (lowest) critical flow velocities and frequencies of oscillation (first model only) of the tested shells.
Finally, future work is suggested with regard to improving the second model and conducting further calculations.
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BOUKERMOUCHE, AHMED. "Mise au point et developpementde mesures de la granulometrie et de la concentration de la phase liquide dans un jet diphasique engendre par des injecteurs coaxiaux." Université Louis Pasteur (Strasbourg) (1971-2008), 1989. http://www.theses.fr/1989STR13080.
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Dans le cadre des travaux de cette these, nous avons propose, en premier lieu, une modification a la methode de mesure de la granulometrie basee sur la mesure des piedestaux; celle-ci consiste a determiner la fonction de repartition des piedestaux, au lieu de la densite de probabilite. Cette methode a servi a l'etude des jets engendres, par des injecteurs coaxiaux. En deuxieme lieu, nous avons effectue des mesures de la concentration locale en phase liquide, en proposant d'une part, la mesure de celle-ci par la methode de la diffusion de la lumiere, et d'autre part par la methode de comptage opto-electronique des particules traversant le volume de mesure d'un anemometre laser-doppler. L'etude de la concentration nous a amene a nous interesser a la diffusivite turbulente, et au nombre de schmidt. En considerant les profils mesures des vitesses de l'air et des concentrations le long du jet, on a pu calculer les distributions de la diffusivite turbulente equivalente et d'evaluer l'evolution du nombre de schmidt le long de l'axe du jet
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Elouadie, Larbi. "Electroconvection et augmentation des échanges thermiques produites par une injection unipolaire en géométrie fil- cylindre coaxiaux." Grenoble 1, 1991. http://www.theses.fr/1991GRE10121.
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L'application d'un champ electrique a un liquide dielectrique suffisamment isolant, produit en general une injection unipolaire qui met le liquide en mouvement. Cette electroconvection, ainsi que son effet sur l'augmentation des echanges thermiques sont etudies dans la geometrie fil-cylindre coaxiaux. En absence d'ecoulement force, les deux regimes d'electroconvection (respectivement domines par les effets visqueux et inertiels) sont mis en evidence. L'analogie avec le cas plan permet d'estimer l'ordre de grandeur de la vitesse caracteristique du liquide. La valeur beaucoup plus elevee que dans le cas plan de la tension de transition entre les deux regimes de convection est due a la geometrie. La superposition d'un ecoulement force a l'injection unipolaire produit un entrainement de charge, ainsi qu'une diminution de la valeur caracteristique de la composante radiale de la vitesse du liquide. Des arguments qualitatifs permettent de rendre compte de l'influence du nombre de reynolds de l'ecoulement force sur l'entrainement de charge et la diminution du courant. La turbulence est alimentee aussi bien par l'ecoulement force que par l'action de la force de coulomb. Ceci ressort de la bonne correlation entre la perte de charge et la somme des puissances mecanique et electrique fournies au systeme. La force de coulomb qui s'exerce sur les charges injectees determine principalement l'etat d'agitation du liquide et par consequent l'importance des echanges thermiques. Les mesures montrent que les echanges thermiques peuvent etre augmentes jusqu'a un rapport dix. La meilleure correlation est obtenue entre le nombre de nusselt et un parametre incluant l'energie electrique fournie au systeme et definit une loi de puissance. Il apparait que l'ecoulement force n'agit pas directement mais seulement en diminuant le courant total. Finalement, l'estimation du nombre de reynolds turbulent permet de comparer l'effet de l'electroconvection a celui de la turbulence generee par l'ecoulement en conduite (re>2000)
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Örlü, Ramis. "Experimental studies in jet flows and zero pressure-gradient turbulent boundary layers." Doctoral thesis, KTH, Mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10448.
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This thesis deals with the description and development of two classical turbulent shear flows, namely free jet and flat plate turbulent boundary layer flows. In both cases new experimental data has been obtained and in the latter case comparisons are also made with data obtained from data bases, both of experimental and numerical origin. The jet flow studies comprise three parts, made in three different experimental facilities, each dealing with a specific aspect of jet flows. The first part is devoted to the effect of swirl on the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of combined X-wire and cold-wire anemometry. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air. The second jet flow part was set out to test the hypothesis put forward by Talamelli & Gavarini (Flow, Turbul. & Combust. 76), who proposed that the wake behind a separation wall between two streams of a coaxial jet creates the condition for an absolute instability. The experiments confirm the hypothesis and show that the instability, by means of the induced vortex shedding, provides a continuous forcing mechanism for the control of the flow field. The potential of this passive mechanism as an easy, effective and practical way to control the near-field of interacting shear layers as well as its effect towards increased turbulence activity has been shown. The third part of the jet flow studies deals with the hypothesis that so called oblique transition may play a role in the breakdown to turbulence for an axisymmetric jet.For wall bounded flows oblique transition gives rise to steady streamwise streaks that break down to turbulence, as for instance documented by Elofsson & Alfredsson (J. Fluid Mech. 358). The scenario of oblique transition has so far not been considered for jet flows and the aim was to study the effect of two oblique modes on the transition scenario as well as on the flow dynamics. For certain frequencies the turbulence intensity was surprisingly found to be reduced, however it was not possible to detect the presence of streamwise streaks. This aspect must be furher investigated in the future in order to understand the connection between the turbulence reduction and the azimuthal forcing. The boundary layer part of the thesis is also threefold, and uses both new data as well as data from various data bases to investigate the effect of certain limitations of hot-wire measurements near the wall on the mean velocity but also on the fluctuating streamwise velocity component. In the first part a new set of experimental data from a zero pressure-gradient turbulent boundary layer, supplemented by direct and independent skin friction measurements, are presented. The Reynolds number range of the data is between 2300 and 18700 when based on the free stream velocity and the momentum loss thickness. Data both for the mean and fluctuating streamwise velocity component are presented. The data are validated against the composite profile by Chauhan et al. (Fluid Dyn. Res. 41) and are found to fulfil recently established equilibrium criteria. The problem of accurately locating the wall position of a hot-wire probe and the errors this can result in is thoroughly discussed in part 2 of the boundary layer study. It is shown that the expanded law of the wall to forth and fifth order with calibration constants determined from recent high Reynolds number DNS can be used to fix the wall position to an accuracy of 0.1 and 0.25 l_ * (l_* is the viscous length scale) when accurately determined measurements reaching y+=5 and 10, respectively, are available. In the absence of data below the above given limits, commonly employed analytical functions and their log law constants, have been found to affect the the determination of wall position to a high degree. It has been shown, that near-wall measurements below y+=10 or preferable 5 are essential in order to ensure a correctly measured or deduced absolute wall position. A number of peculiarities in concurrent wall-bounded turbulent flow studies, was found to be associated with a erroneously deduced wall position. The effect of poor spatial resolution using hot-wire anemometry on the measurements of the streamwise velocity is dealt with in the last part. The viscous scaled hot-wire length, L+, has been found to exert a strong impact on the probability density distribution (pdf) of the streamwise velocity, and hence its higher order moments, over the entire buffer region and also the lower region of the log region. For varying Reynolds numbers spatial resolution effects act against the trend imposed by the Reynolds number. A systematic reduction of the mean velocity with increasing L+ over the entire classical buffer region and beyond has been found. A reduction of around 0.3 uƬ, where uƬ is the friction velocity, has been deduced for L+=60 compared to L+=15. Neglecting this effect can lead to a seemingly Reynolds number dependent buffer or log region. This should be taken into consideration, for instance, in the debate, regarding the prevailing influence of viscosity above the buffer region at high Reynolds numbers. We also conclude that the debate concerning the universality of the pdf within the overlap region has been artificially complicated due to the ignorance of spatial resolution effects beyond the classical buffer region on the velocity fluctuations.QC 20100820
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Suen, Chung-Yuen, and 孫鍾右. "flow patterns of the coaxial jets." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/63200952632453253318.
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Perez, Ronald Jose Doblado, and 杜洛德. "Development of A Coaxial Pipe Flow Generator." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/73703166468831183393.
Full textAbstract:
碩士崑山科技大學
機械工程研究所
99
This study aims to research and develop of A Coaxial Pipe Flow Generator. This generator is based in a horizontal coaxial turbine. Computer Aided Design software were used to design the turbine and the other components of the mechanism. Modern engineering tools such as Computational Fluid Dynamics (CFD) software and Rapid Prototyping (RP) technology are utilized to facilitate the numerical and experimental studies. The CFD numerical simulations consist of three-dimensional steady analyses. These simulations were conducted to find the relationship between the flow rate, blade geometry and number of blades. During the experimentation process, Rapid Prototyping Technology was used to fabricate many different types of turbine geometries to test different impeller parameters. The stator coil was redesigned to increase the performance of the generator and to test the generator under different conditions. RPM and voltages where measured for each turbine design. The study leads to several important findings for better pipe flow generator design.
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Lin, Yeong-Chern, and 林永成. "Recirculation Zone of Annular Swirling Flow and Confined Boundary of Annular Flow with Coaxial Jets." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/97789026924719234282.
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紀一珍. "Numerical Modeling on the Fuel Nozzle with Dual Coaxial Swirling Flow." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9zy6x9.
Full textAbstract:
碩士高苑科技大學
機械與自動化工程研究所
107
An environmental clean and high performance turbojet engine highly depends on a large degree of the optimized control of fuel supply, fuel atomization and fuel/air mixing in the combustor. In the present study, a homemade air blast fuel nozzle with dual coaxial swirling Flow was numerically studied. The velocity of droplets, the distribution of droplets and vapor of spray, and the stream line for six specific conditions were evaluated. Briefly, the fundamental results from this study will provide essential background and database for designing fuel nozzle for advanced turbofan engine in Taiwan for domestic or military application.
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SUNG, CHEN-YU, and 宋振宇. "Experimental Study on Effects of Flow-Field with PIV-Method for Coaxial Rotors." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/50925227999228493868.
Full textAbstract:
碩士逢甲大學
航太與系統工程學系
105
This study presents the results of the rotors aerodynamic for a coaxial helicopter. The main purpose of our research was to estimate the optimum airfoil and upgrade wingtip design. For this study we employed the airfoil of the asymmetric Viper-X rotor, this study compared the aerodynamic performance of the Viper-X with the common symmetric airfoil NACA0012, and derived an improved asymmetric swept rotor design based on the asymmetric rotor Viper-X. Different rotor wingtips affect both the thrust output of the upper rotors and lower rotors, as well as aerodynamic outcomes. Symmetric rotors, asymmetric rotors and asymmetric swept rotors all present particular advantages under individual flight conditions. However, the optimal output of each type of rotor depends on the effect of the coupling of the flow field and the influence of the eddy current structure on the aerodynamic performance of the coaxial rotors. Our numerical calculations show that among the asymmetric airfoil series, the A-20 rotor presents the best performance under all the simulated flight conditions. In addition, we discuss the results of the PIV experiment conducted for this study where we employed different coaxial rotors: NACA0012, A-0, A-20, A-35 and A-40 and A-50r rotors. We demonstrate that the A-20 presents the most optimal performance when the upper and lower coaxial rotors intersect during the specific flight conditions for this experiment results. Our method employing experimental coaxial rotors in the conduction of the PIV flow field experiment allowed us to observe the different effects in a hover state. We tested the weight of the air-load, the complexity of flow filed vortex distribution, and the robustness of the vortex structure. We concluded that both the asymmetric rotors and the asymmetric swept rotors present similar optimal outcomes in terms of aerodynamic performance. Nevertheless, the asymmetric A-20 swept rotor appears to be the most suitable option according to our research seeking the best aerodynamic effect of the rotor.
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Chang, Yu-Lung, and 張友隆. "The development of the aqueous-organic liquid-liquid micro-extraction technology with continuous coaxial flow." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/n8x3rb.
Full textAbstract:
碩士國立中興大學
機械工程學系所
106
In recent years, bioengineering technology has flourished and is widely used in the pharmaceutical industry. From raw materials to processed drugs, it can be roughly divided into upstream pretreatment, midstream reaction and downstream purification. Each stage contains various bioprocessing technology. As long as you change one parameter of the steps, it will affect the yield. It also makes the drug development in the process takes a lot of money and time. In order to reduce the production cost, the techniques for miniaturizing devices in bioengineering have also emerged. The final output and quality of the product are mainly affected by downstream processing. The downstream processing utilizes the different physical properties and chemical properties of the reactants in process to separate and purify the product. In this study, the miniaturization system for liquid-liquid extraction was discussed. Among the existing miniaturized liquid-liquid extraction systems, there are three of the most common techniques: droplet based liquid-liquid extraction, membrane based liquid-liquid and co-flow liquid-liquid extraction systems. The development of these three technologies is limited in their use. But these three technologies are limited in their use. In order to overcome the limitations of the above three technologies, the purpose of this study was to develop a system that can be continuously flowed, has a wide operating range, has a stable aqueous-organic phase contact area, and does not require an additional liquid separation device. To achieve the purpose, a helix wire is added into the device to make the aqueous solution flow only in the helix wire and form a stable contact surface with the organic solvent due to the Laplace pressure. The extraction is carried out by continuous coaxial flow; The pitches of the helix wire are adjustable by stretching or compressing the helix wire. To allow the device to have a stable liquid contact area at different flow rates to complete the extraction. The system also optimizes bioprocessing efficiency by changing contact time, pH, and changing extractant. In the study, the aqueous phase contained 50 mM of -methylbenzylamine (-MBA) and acetophenone (APH), and the organic solvent phase was n-heptane, which was used to simulate the purification operations in the acetophenone production process. In the experiment, the applicable operating range of helix wire pitches are from 0.156 to 0.335 mm was tested. From the experimental results, the operating range was from 0.5 to 7300 l/min, and no droplet was formed in the other phase liquid. After the flow rate is applied, the extraction efficiency in the device at different settings is also verified.
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Santhosh, R. "Transition and Acoustic Response of Vortex Breakdown Modes in Unconfined Coaxial Swirling Flow and Flame." Thesis, 2015. http://etd.iisc.ernet.in/2005/3856.
Full textAbstract:
The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies.
The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801.
In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold
excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude.
In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.
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Liu, Yu-Tsung, and 劉育宗. "Thermal and Fluid Field Analysis of Coaxial Flow Issuing From a RF-driven Atmospheric-Pressure Plasma Jet." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/00097080360466499634.
Full textAbstract:
碩士國立交通大學
機械工程系所
96
APPJs have found applications in surface modification, surface cleaning, sterilization, thin-film deposition and etching, to name a few. Most experimental studies empasized on the electrical properties such as the power deposition and I-V curve. Measurements of flow field are not seen in the literature, which is otherwise very important from the viewpoint of applications. This study aims to understand the structure of flow and thermal field which issues from a coaxial atmospheric-pressure plasma jet (APPJ). The control parameters of the experiment: Ar gas flow rate, 10,15,20 slm, RF power source for 80,120,150 W, We get the velocity distribution by using the particle image velocimetry (PIV), get the temperature distribution by using the thermocouple (TC), and get the radicals intensity distribution by using the Optical Emission Spectroscopy (OES). Experiment content is divided into three parts. The first part is to get the velocity distribution of the exit from the jet with and without plasma. The second part is to measure the temperature distribution of the exit from the jet at different flow rates and different input power. The final part is to measure the intensity of radicals along the exit from the jet and use V-I probe to measure the electrical property with and without seeding particles. The distribution of velocity increased slightly with the input power. As the gas flow rate increased, the temperature of coaxial flow issuing from the jet would be deceased. But the change is not clearly. OES measurement from the experimental results can be known that the plasma can generate a lot of oxygen radicals at 0~4mm from the jet. V-I probe measurement from the experimental results can be know that the electrical properties with seeding and without seeding are different.
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Doung, Yu-Cheng, and 董育成. "Analysis on Concentration Distribution of Mehane Flames in a Coaxial SPF and Flow Field of a Rotating SPF." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/07270743716994433651.
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碩士國立成功大學
機械工程研究所
82
@ 在研究紊流燃燒場特性時，火燄除了垂直方向的作用外，平行於火燄 間相互作用的影響也是不可被忽略的。一般實際所使用的燃燒器其燃燒場 大多處於紊流燃燒的狀態,而由於燃燒行為本身是一種劇烈的質量及能量 的交換過程,因此對於紊流燃燒場現象的研究將更為複雜但也更為重要。 本文之第一部份藉由停滯面同軸燃燒場的濃度量測探討平行火燄面間的質 傳效應,以幫助吾人對紊流燃燒場特性及火燄結構有進一步的認識。在實 驗中,吾人保持同軸燃燒器內外管出口流速為 60 cm/sec ,並於燃燒器內 通入三種不同濃度的甲烷可燃流。其濃度分別為(7,0),(9,35) 及(11.5,35)石英玻璃停滯面與同軸燃燒器出口之距離為 12mm 。在高溫 氣體的採樣方面則是以具有急冷(quench)效果的石英探針(probe)配合氣 體集氣瓶進行。此後再將採樣氣體通入氣體層析儀(gas chromatograph) 內進行濃度組成分析。本文之第二部份則藉由停滯面旋轉流場的數值計算 探討剛體旋轉運動對停滯面旋轉流場的影響。吾人利用有限體積的數值方 法，配合冪次法則以SIMPLER 之原理對有限間距之停滯面旋轉噴流進行冷 流場分析並與實驗數據進行比較分析。其結果顯示,數值計算與實驗二者 於低轉速時相當接近,但在高轉速時,數值計算與實驗二者有些差距,但二 者之趨勢則是相同的。
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Fier, Jeffrey Michael. "Part I. Fold Continuation and the Flow Between Rotating, Coaxial Disks. Part II. Equilibrium Chaos. Part III. A Mesh Selection Algorithm for Two-Point Boundary Value Problems." Thesis, 1985. https://thesis.library.caltech.edu/1162/1/Fier_jm_1985.pdf.
Full textAbstract:
Part I:
We consider folds in the solution surface of nonlinear equations with two free parameters. A system of equations whose solutions are fold paths is formulated and proved to be non-singular in a neighborhood of a fold, thus making continuation possible. Efficient numerical algorithms employing block Gaussian elimination are developed for applying Euler-Newton pseudo-arclength continuation to the system, and these are shown to require fewer operations than other methods.
To demonstrate the use of these methods we calculate the flow between two infinite, rotating disks. For Reynold's number less than 1000, six separate solution sheets are found and completely described. Plots of 47 solutions for three values of the disk speed ratio and for Reynold's number equal to 625 are shown. These are compared with the solutions found by previous investigators.
Part II:
Two ordinary differential equations with parameters whose solution paths exhibit an infinite sequence of folds clustered about a limiting value are studied. Using phase-plane analysis, expressions for the limiting ratios of the parameter values at which these folds occur are derived and the limiting values are shown to be non-universal.
Part III:
A mesh selection algorithm for use in a code to solve first-order nonlinear two-point boundary value problems with separated end conditions is described. The method is based on equidistributing the global error of the box scheme, a numerical estimate of which is obtained from Richardson extrapolation. Details of the algorithm and examples of its performance on non-stiff and stiff problems are presented.
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Chen, Shiarng-Jiang, and 陳祥江. "Predictions on Flame Surfaces in Coaxial Combustible Flows." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/94755652122746559798.
Full textAbstract:
碩士國立成功大學
機械工程研究所
81
Because the mechanism of turbulent combustion is compl- icated , so many experimental and analytical studies have considered laminar premixed or diffusion flames.Previous experimental investigations on flame interaction utilize counterflow configuration ; in the present investigation , stagnation- point coaxial flows were made using coaxial bur- ners and quartz plate. The interaction between inner and outer coaxial flames is experimentally investigated in det- ail. Experimental results show that , under the condition of Le<1 or Le>1 ,the outer flame is more easier flashback than the inner flame. Also the instabilities of flames are obse- rved in the experiment. The shape and location of flames in a combustible coax- ial counterflow are theoretically predicted in this paper . The distributions of velocity and concentration in the non- reactive flow were numerically calculated by the finite-vo- lume method incorporated with the SIMPLER algorithm and the power-law scheme. The surface of a premixed flame is deter- mined on the basis of the balance betwen the flame velocity and the flow velocity normal to the flame surface at the upstream edge of the premixed flame. The surface of a diff- usion flame is identified by the iso-concentration line in the flow field. The predictions are finally compared with the previous experimental observations in the stagnation- point coaxial flows.
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Yi-ShengChen and 陳以昇. "Symmetry breaking of the flow between two coaxially counter rotating circular disks." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/41466551132791301443.
Full textAbstract:
碩士國立成功大學
機械工程學系碩博士班
101
The swirling flow between two coaxial counter-rotating disks may not be the only one solution given different aspect ratios of the rotating disks or different Reynolds numbers. Therefore, in the present study, it discusses the relation between aspect ratio and critical Reynolds number choosing different boundary conditions and compares these results with academic. In particular, there are two cases about free surface and solid boundary respectively with two coaxial counter-rotating disks. Specifically, ANSYS FLUENT simulations are performed the motions of the flow constructing 2D axisymmetric and 3D models and are found the critical Reynolds number by changing the angular speeds. The results show that critical Reynolds number first decreases and then increases as the aspect ratio increases in free surface case. Moreover, it is found that case of the solid boundary and the motion of the flow is similarity qualitatively with free surface case. In quantitative, it is overall right shift about aspect ratio of 1 unit and the critical Reynolds number is higher three hundred in solid boundary. Finally, it is found that the boundary academic chose appears like the cases of free surface and solid boundary in qualitative. But it shows that it is overall left shift about aspect ratio of 0.1 to 0.5 unit and the critical Reynolds number is between them quantitatively.