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A comparison between stall prediction models for axial flow compressorsGill, Andrew 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2006. / ENGLISH ABSTRACT: The Stellenbosch University Compressor Code (SUCC) has been developed for the purpose
of predicting the performance of axial flow compressors by means of axisymmetric inviscid
throughflow methods with boundary layer blockage and empirical blade row loss models.
This thesis describes the process of the implementation and verification of a number of stall
prediction criteria in the SUCC. In addition, it was considered desirable to determine how
certain factors influence the accuracy of the stall prediction criteria, namely the nature of
the computational grid, the choice of throughflow method used, and the use of a boundary
layer blockage model and a radial mixing model. The stall prediction criteria implemented
were the di®usion factor limit criterion, de Haller's criterion, Aungier's blade row criterion,
Aungier's boundary layer separation criterion, Dunham's, Aungier's and the static-to-static
stability criteria. The compressors used as test cases were the Rofanco 3-stage low speed
compressor, the NACA 10-stage subsonic compressor, and the NACA 5-stage and 8-stage
transonic compressors. Accurate boundary layer blockage modelling was found to be of great
importance in the prediction of the onset of stall, and that the matrix throughflow Method
provided slightly better accuracy than the streamline curvature method as implemented in
the SUCC by the author. The ideal computational grid was found to have many streamlines
and a small number of quasi-orthogonals which do not occur inside blade rows. Radial mixing
modelling improved the stability of both the matrix throughflow and streamline curvature
methods without significantly affecting the accuracy of the stall prediction criteria. De
Haller's criterion was over-conservative in estimating the stall line for transonic conditions,
but more useful in subsonic conditions. Aungier's blade row criterion provided accurate
results on all but the Rofanco compressor. The diffusion factor criterion provided over-
optimistic predictions on all machines, but was less inaccurate than de Haller's criterion
on the NACA 5-stage transsonic machine near design conditions. The stability methods
performed uniformly and equally badly, supporting the claims of other researchers that they
are of limited usefulness with throughflow simulations. Aungier's boundary layer separation
method failed to predict stall entirely, although this could reflect a shortcoming of the
boundary layer blockage model. / AFRIKAANSE OPSOMMING: Die Stellenbosch University Compressor Code (SUCC) is ontwikkel om die prestasie van aksiaalvloei kompressors te voorspel met behulp van aksisimmetriese nie-viskeuse deurvloeimetodes met grenslaagblokkasie en empiriese modelle vir die verliese binne lemrye. Hierdie tesis
beskryf die proses waarmee sekere staakvoorspellingsmetodes in die SUCC geïmplementeer
en geverifieer is. Dit was ook nodig om die effek van sekere faktore, naamlik die vorm
van die berekeningsrooster, die keuse van deurvloeimetode en die gebruik van `n grenslaagblokkasiemodel en radiale vloeivermengingsmodel op die akuraatheid van die staakvoorspellingsmetodes te bepaal. Die staakvoorspellingsmetodes wat geïmplementeer is, is die
diffusie faktor beperking metode, de Haller se metode, Aungier se lemrymetode, Aungier
se grenslaagmetode en die Dunham, Aungier en die statiese-tot-statiese stabiliteitsmetodes.
Die kompressors wat gebruik is om die metodes te toets is die Rofanco 3-stadium lae-spoed
kompressor, die NACA 10-stadium subsoniese kompressor en die NACA 5- en 8-stadium
transsoniese kompressors. Daar is vasgestel dat akkurate grenslaagblokkasie modelle van
groot belang was om `n akkurate aanduiding van die begin van staking te voorspel, en dat,
vir die SUCC, die Matriks Deurvloei Metode oor die algemeen 'n bietjie meer akkuraat as die
Stroomlyn Kromming Metode is. Daar is ook vasgestel dat die beste berekeningsrooster een
is wat baie stroomlyne, en die kleinste moontlike getal quasi-ortogonale het, wat nie binne
lemrye geplaas mag word nie. Die numeriese stabiliteit van beide die Matriks Deurvloei
en die Stroomlyn Kromming Metode verbeter deur gebruik te maak van radiale vloeivermengingsmodelle, sonder om die akkuraatheid van voorspellings te benadeel. De Haller
se metode was oorkonserwatief waar dit gebruik is om die staak-lyn vir transsoniese vloei
toestande, maar meer nuttig in die subsoniese vloei gebied. Aungier se lemrymetode het
akkurate resultate gelewer vir alle kompressors getoets, behalwe die Rofanco. Die diffusie
faktor metode was oor die algemeen minder akuraat as Aungier se metode, maar meer akkuraat as de Haller se metode vir transsoniese toestande. Die stabiliteitsmetodes het almal ewe
swak gevaar. Dit stem ooreen met die bevindings van vorige navorsing, wat bewys het dat
hierdie metodes nie toepaslik is vir simulasies wat deurvloeimetodes gebruik nie. Aungier se
grenslaagmetode het ook baie swak gevaar. Waarskynlik is dit as gevolg van tekortkomings
in die grenslaagblokkasiemodel.
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Design and development of a pulsatile axial flow blood pump as a left ventricular assist devicePatel, Karnal January 2012 (has links)
Each year all over the world, Millions of patients from infants to adults are diagnosed with heart failure. A limited number of donor hearts available for these patients results in a tremendous demand of mechanical circulatory support (MCS) system, either in the form of total artificial heart (TAH) or a ventricular assist device (VAD). Physiologically MCS are expected to provide heart; a time to rest and potential recovery by unloading the ventricle, while maintaining the adequate peripheral as well as coronary circulation. Existing ventricular assist devices (VAD) have employed either displacement type pulsatile flow pumping systems or continuous flow type centrifugal/rotodynamic pumps systems. Displacement type devices produce a pulsatile outflow, which has significant benefits on vital organ function and end organ recovery. Continuous flow devices are small and can be placed within body using minimal invasive procedures, in addition they reduces infection as well as mechanical failure related complications. Despite availability of success stories for both types of pumping systems, the selection of the either of them is an ongoing debate. This thesis aims to merge the advantages of displacement pumps (pulsatile flow) and axial-flow pumps (continuous flow) into a novel left vertical assist device (LVAD), by designing a novel minimal invasive, miniature axial-flow pump producing pulsating outflow for the patients having early heart failure and myocardial infarction as a Bridge-To-Recovery (BTR) or Bridge-To-Decision (BTD) device. The design of VAD, the experimental setup and dedicated control system were developed for the in vitro evaluation of pulsatile flow. Computational fluid dynamics (CFD) had been employed for the detail investigation of pulsatile flow. In addition, CFD was also applied to optimize the pulse generation for low haemolysis levels. Outcome of the study produces comprehensive understanding for the generation of pulsatile flow using an axial flow pump. Further, it provides the means of generating a controlled pulse that can regulate flow rate for varying heart rate within low haemolysis levels.
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Forces fluides stationnaires exercées sur un cylindre déformé en écoulement axial et confiné - application au dimensionnement sismique des assemblages combustibles / Steady fluid forces on a deformed cylinder in axial and confined flow. Application to the seismic design of fuel assembliesJoly, Aurélien 07 November 2018 (has links)
Les phénomènes d’interaction fluide-structure jouent un rôle important dans le calcul de tenue au séisme des assemblages combustibles. Afin de quantifier les marges de dimensionnement, le modèle de forces fluides utilisé doit être validé et affiné. Pour cela, des campagnes d’essais à l’échelle industrielle ont été réalisées en amont de la thèse. L’objectif ici est de contribuer à l’interprétation des essais industriels pour le cas stationnaire, et de valider les méthodes numériques permettant de simuler ce type d’écoulement. La problématique industrielle s'inscrit dans la tradition de l'étude des structures élancées sous écoulement axial. Le modèle de force fluide locale généralement utilisé, que nous appelons modèle de Taylor-Lighthill-Païdoussis (TLP), consiste en stationnaire à combiner un terme de force fluide potentielle, proportionnel à la courbure, et un terme de force fluide visqueuse, proportionnel à la pente. Des versions dynamiques de ce modèle ont été employées avec succès pour prédire le comportement vibratoire de cylindres flexibles en écoulement axial. Néanmoins, la littérature propose très peu de données de validation directe de cette représentation des forces fluides. Afin d’acquérir de telles données, pour le cas particulier d’un cylindre confiné dans un réseau de cylindres, un nouveau banc d’essai a été conçu et mis en place au laboratoire. Il s’agit d’un faisceau de 3x3 cylindres disposé dans une veine de soufflerie. Le cylindre central possède trois degrés de liberté : rotation, translation, flexion. Les efforts fluides résultants sont mesurés à l’aide d’une balance. Un modèle numérique similaire à la maquette est aussi réalisé et donne accès aux forces fluides locales. Les forces globales obtenues numériquement et expérimentalement sont comparables. Les forces locales obtenues dans les simulations numériques s’expliquent bien à l’aide du modèle TLP, en ignorant les effets de bord à l’entrée et à la sortie du faisceau. La transposition au cas industriel, de géométrie plus complexe, est réalisable par recalage des coefficients du modèle. / Fluid-structure interaction phenomena play a major role in the seismic design of fuel assemblies. In order to evaluate the design margins, the implemented model of fluid forces needs to be carefully assessed. Industrial-scale tests have been carried out with that purpose. Our goal is to contribute to their interpretation in the steady case, and to validate CFD methods usually applied to the type of flow at stake here. This fits in the tradition of the study of slender structures in axial flow. The local steady fluid forces decompose in a potential term, which is proportional to the curvature of the structure, and a viscous term, proportional to the angle of incidence. Adapted versions of this representation, which we call Taylor-Lighthill-Païdoussis (TLP) model, have proved successful in predicting the dynamic behaviour of flexible cylinders in axial flow. However, there is a lack in the literature of sound validation data for the fluid forces themselves. In order to gather such data, a new test rig has been designed and built. It consists in a 3x3 cylinder bundle confined in a wind tunnel. The central cylinder can be rotated, translated or bent. Resultant fluid forces are measured using a load cell. CFD calculations give access to the local fluid forces. CFD and experiments give similar results on the global fluid forces. The TLP model performs well at predicting the local fluid forces, except in the inlet and outlet regions. It can be fitted to the industrial case by adapting its coefficients.
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Design Of An Axial Flow Fan For A Vertical Wind Tunnel For ParatroopersCevik, Fatih 01 December 2010 (has links) (PDF)
Free fall is one of the important phases of the operation performed by the Special Forces paratroopers. Also civilian parachutists are performing free fall as a sport by doing aerobatic maneuvers when they reach the terminal
velocity during falling before opening their parachutes. Vertical wind tunnels are used for training the parachutists and paratroopers. It is safe, cheap and more convenient when compared to jumping out of an airplane.
This thesis consists of aerodynamic design of closed circuit, double return vertical wind tunnel with a flight section that can accommodate four paratroopers, aerodynamic design of a rotor straightener configuration axial flow fan and running CFD analysis of the axial flow fan for different operating conditions by FLUENT software.
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Widefield fluorescence correlation spectroscopyNicovich, Philip R. 26 March 2010 (has links)
Fluorescence correlation spectroscopy has become a standard technique for modern biophysics and single molecule spectroscopy research. Here is presented a novel widefield extension of the established single-point technique. Flow in microfluidic devices was used as a model system for microscopic motion and through widefield fluorescence correlation spectroscopy flow profiles were mapped in three dimensions. The technique presented is shown to be more tolerant to low signal strength, allowing image data with signal-to-noise values as low as 1.4 to produce accurate flow maps as well as utilizing dye-labeled single antibodies as flow tracers. With proper instrumentation flows along the axial direction can also be measured. Widefield fluorescence correlation spectroscopy has also been utilized to produce super-resolution confocal microscopic images relying on the single-molecule microsecond blinking dynamics of fluorescent silver clusters. A method for fluorescence modulation signal extraction as well as synthesis of several novel noble metal fluorophores is also presented.
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Design And Performance Analysis Of A Reversible Axial Flow FanKokturk, Tolga 01 June 2005 (has links) (PDF)
Reversible axial flow fans are used as emergency ventilation fans to discharge the smoke generated on the probable fires occurring in the underground transportation systems and mines as quickly as possible, without causing any harm to people exposed to it. The fans which are placed in different configurations according to the location of fire must be able to work bi-directionally, namely reversible. Due to this fact, the blade profiles of the fan must possess the same aerodynamic performance while working on either discharge or suction condition of the fan, dictated by direction of the rotation.
This manuscript consists of the computation of the aerodynamic performances of symmetrical blade profiles of fully reversible axial fans by computational fluid mechanics (CFD) methods, developing a methodology for the design of reversible axial fans and analysis of the designed fan with CFD methods. The aerodynamic performances of the blade cascades are evaluated using FLUENT 6.0 software for different Reynolds numbers, solidities and angle of attacks of the cascade. The results of these computations are embedded into the developed methodology. Performance analysis of the reversible axial flow fan, which is designed with the developed methodology, is done with CFD techniques.
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[pt] ESTUDO EXPERIMENTAL DO ESCOAMENTO AXIAL ATRAVÉS DE REGIÃO ANULAR COM ROTAÇÃO DO CILINDRO INTERNO / [en] EXPERIMENTAL STUDY OF AXIAL FLOW THROUGH AND ANNULAR REGION WITH INNER CYLINDER ROTATION08 May 2008 (has links)
[pt] O escoamento entre cilindros concêntricos com rotação do
cilindro interno com a imposiçãao de um gradiente axial de
pressão foi estudado experimentalmente. A razão de raios
era (n)= 0, 64 e razão de aspecto era (r) = 265. O fator de
atrito e campos de velocidade foram estudados para quatro
rotações diferentes do cilindro interno e para os três
regimes de escoamento, laminar, transição laminar-
turbulento, e turbulento. Os Campos de velocidades foram
obtidos através da técnica de Velocimetria
por Imagem de Partículas (PIV). Os resultados para os
fatores de atrito revelaram que a influência da rotação é
mais pronunciada para regimes laminares e de transição.
Para estes dois regimes o aumento observado foi
de 100% de f/f0. Para o regime de escoamento turbulento, o
aumento foi decrescendo gradativamente até o valor de 10%
de f/f0 para Reaxial = 8458. Os campos de velocidade
instantâneos relevaram padrões complexos do escoamento. Os
perfis de velocidade axial médios tomavam uma forma
achatada com o aumento da rotação do cilindro interno e do
número de Reynolds axial. Para o regime de escoamento
turbulento a influência da rotação do cilindro nos perfis
de velocidade era pequena. / [en] The flow between concentric cylinders with an inner
rotating cylinder with an imposed pressure-driven axial
flow was studied experimentally. The radius ratio was (n) =
0, 64 and the aspect ration was (r) = 265. Friction factor
and velocity fields were studied for four rotations of the
inner cylinder and for laminar, transitional, and turbulent
flow. Velocity fields were measure by Particle Image
Velocimetry (PIV). The results for friction factor showed
that the influence of the rotation is more apparent for
laminar and transitional flow, increasing with the rotation
of the inner cylinder. For these two flows,
the increasing was 100% of f/f0. For turbulent flow, the
increasing was gradualy decreasing to 10% of f/f0 for
Reaxial = 8458. Instantaneous velocity fields showed
complex flow patterns. The time average axial velocity
profiles showed a top hat like form with the increasing of
inner cylinder rotation and axial Reynolds numbers. For
turbulent flow, the influence of rotation in the velocity
profiles was small.
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Reverzační turbokompresor / Reverse TurbochargerZygmont, Martin January 2011 (has links)
The diploma thesis consists of a theoretical part, which deals with the description of reversing turbocharger and its components. The following part is devoted to calculating the radial-axial compressor and turbine. It also performs a calculation of gear box and characteristics of the turbine.
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Die invloed van versteurde inlaatvloeipatrone op aksiaalwaaiersVisser, J. G. J. 12 1900 (has links)
Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. / Thesis (MEng)--Stellenbosch University, 1990. / ENGLISH ABSTRACT: The causes of disturbances in the flow patterns at the
inlets of axial flow fans that are used in mechanical draft
cooling towers and the effects of these disturbances on the
fans, were investigated.
A scale model of a part of a mechanical draft cooling tower
used at a power station was built for the purpose of this
study. In the cooling tower the axial flow fans are
arranged in a matrix configuration. It was noted from the
scale model that the boundary fan was subjected to the
worst inlet disturbances and this had an adverse effect on
the flow it produced. Geometric alterations like the use
of guide vanes and rounded inlets improved the flow through
the boundary fan considerably. It was found that the
performance of the fans is a function of the number of fans
used and the elevation of the fans.
Several tests to determine the performance of the cooling
tower confirmed the results obtained from the experiments
on the scale model. It was also found that the speed and
direction of the prevailing wind have a significant effect
on the cooling tower.
Experiments to investigate the effects of cross-flow at the
inlet of a fan indicated an increased flow through the fan
at low cross-flow velocities and that the flow decreased at
high cross-flow velocities. / AFRIKAANSE OPSOMMING: Die invloed en oorsake van versteurde inlaatvloeipatrone op
aksiaalwaaiers wat in meganiese-trek koeltorings gebruik
word is ondersoek.
'n Skaaimodel van 'n deel van 'n meganiese-trek koeltoring
wat by 'n kragstasie gebruik word is gebou vir die doel van
die studie. Die aksiaalwaaiers wat in die koeltoring
gebruik word is in 'n matrikskonfigurasie gerangskik.
Vanaf die skaalmodel is waargeneem dat die randwaaier die
ergste versteuring by die inlaat ervaar, en gevolglik
minder vloei as die res van die waaiers in die opstelling
lewer. Die vloei deur die randwaaier is verbeter deur
verskillende geometriese wysigings soos leilemme en
inlaatafrondings aan te bring. Daar is gevind dat die
werking van die waaiers in die opstelling 'n funksie van
die hoeveelheid waaiers asook die grondvryhoogte is.
Om die werking van die koeltoring te bepaal is verskillende
toetse daarop uitgevoer. Die resultate het die geldigheid
van die skaalmodel bevestig. Daar is ook gevind dat die
heersende windsterkte en rigting 'n definitiewe invloed op
die koeltoring uitoefen.
Die invloed van 'n dwarsvloei by die inlaat van 'n enkele
waaier is ook eksperimenteel ondersoek. Die resultate toon
dat daar 'n vermeerdering in vloei deur die waaier by lae
dwarsvloeisnelhede plaasvind. Hoë dwarsvloeisnelhede
veroorsaak egter 'n vermindering in vloei.
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Design methodology of an axial-flow turbine for a micro jet engineBasson, Johan George Theron 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The main components of a micro gas turbine engine are a centrifugal or mixed-flow compressor, a combustion chamber and a single stage axial-flow or radial-flow turbine. The goal of this thesis is to formulate a design methodology for small axial-flow turbines. This goal is pursued by developing five design-related capabilities and applying them to develop a turbine for an existing micro gas turbine engine. Firstly, a reverse engineering procedure for producing digital three-dimensional models of existing turbines is developed. Secondly, a procedure for generating candidate turbine designs from performance requirement information is presented. The third capability is to use independent analysis procedures to analyse the performance of a turbine design. The fourth capability is to perform structural analysis to investigate the behavior of a turbine design under static and dynamic loading. Lastly, a manufacturing process for prototypes of a feasible turbine design is developed. The reverse engineering procedure employs point cloud data from a coordinate measuring machine and a CT-scanner to generate a three-dimensional model of the turbine in an existing micro gas turbine engine. The design generation capability is used to design three new turbines to match the performance of the turbine in the existing micro gas turbine engine. Independent empirical and numerical turbine performance analysis procedures are developed. They are applied to the four turbine designs and, for the new turbine designs, the predicted efficiency values differ by less than 5% between the two procedures. A finite element analysis is used to show that the stresses in the roots of the turbine rotor blades are sufficiently low and that the dominant excitation frequencies do not approach any of the blade natural frequencies. Finally prototypes of the three new turbine designs are manufactured through an investment casting process. Patterns made of an organic wax-like material and a polystyrene material are used, with the former yielding superior results. / AFRIKAANSE OPSOMMING: Mikro-gasturbiene-enjins bestaan uit 'n sentrifugaal- of ‘n gemende-vloeikompressor, 'n verbrandingsruim en 'n enkel-stadium-aksiaalvloei- of ‘n radiaalvloei-turbine. Die doel van hierdie tesis is om 'n ontwerpsmetodologie vir klein aksiaalvloei-turbines saam te stel. Hierdie doel word deur die ontwikkeling en toepassing van vyf ontwerpsverwante vermoëns nagestreef. Eerstens word 'n tru-waartse-ingenieursproses ontwikkel om drie-dimensionele rekenaarmodelle van die bestaande turbines te skep. Tweedens word 'n metode om kandidaatturbineontwerpe vanaf werkverrigtingsvereistes te verkry, voorgestel. Die derde ontwerpsvermoë is om die werksverrigting van 'n turbineontwerp met onafhanklike analises te evalueer. Die vierde ontwerpsvermoë is om die struktuur van 'n turbinelem te analiseer sodat die effek van statiese en dinamiese belastings ondersoek kan word. Laastens word 'n vervaardigingsproses vir prototipes van geskikte turbineontwerpe ontwikkel. Die tru-waartse-ingenieursproses maak gebruik van 'n koördinaat-meet-masjien en 'n CT-skandeerder om puntewolkdata vanaf die turbine in 'n bestaande mikro-gasturbiene-enjin te verkry. Die data word dan gebruik om 'n drie-dimensionele model van die turbine te skep. Die ontwerpskeppingsvermoë word dan gebruik om drie kandidaatturbineontwerpe vir die bestaande mikro-gasturbiene-enjin te skep. Onafhanklike empiriese en numeriese prosedures om die werkverrigting van 'n turbineontwerp te analiseer word ontwikkel. Beide prosedures word op die vier turbineontwerpe toegepas. Daar word gevind dat die voorspelde benuttingsgraadwaardes van die nuwe ontwerpe met minder as 5% verskil vir die twee prosedures. 'n Eindige-element-analise word dan gebruik om te wys dat die spannings in die wortels van die turbinelemme laag genoeg is, asook dat die dominante opwekkingsfrekwensies nie die lem se natuurlike frekwensies nader nie. Laastens word prototipes van die drie nuwe turbineontwerpe deur 'n beleggingsgietproses vervaardig. In die vervaardigingproses word die effektiwiteit van twee materiale vir die gietpatrone getoets, naamlik 'n organiese wasagtige materiaal en 'n polistireen-materiaal. Daar word bevind dat die gebruik van die wasagtige gietpatrone tot beter resultate lei.
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