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Flow-induced sound and vibration due to the separated shear layer in backward-facing step and cavity configurationsVelikorodny, Alexey S. 25 November 2009 (has links)
Fully turbulent inflow past symmetrically located side branches mounted in a duct can give rise to pronounced flow oscillations due to coupling between separated shear layers and standing acoustic waves. Experimental investigation of acoustically-coupled flows was conducted using digital particle image velocimetry (DPIV) in conjunction with unsteady pressure measurements. Global instantaneous, phase- and time-averaged flow images, as well as turbulence statistics, were evaluated to provide insight into the flow physics during flow tone generation. Onset of the locked-on resonant states was characterized in terms of the acoustic pressure amplitude, frequency and the quality factor of the resonant pressure peak. Structure of the acoustic noise source is characterized in terms of patterns of generated acoustic power. In contrast to earlier work, the present study represents the first application of vortex sound theory in conjunction with global quantitative flow imaging and numerical simulation of the 2D acoustic field.
In addition to the basic side branch configuration, the effects of bluff rectangular splitter plates located along the centerline of the main duct was investigated. The first mode of the shear layer oscillation was inhibited by the presence of plates, which resulted in substantial reduction of the amplitude of acoustic pulsations and the strength of the acoustic source. These results can lead to the development of improved control strategies for coaxial side branch resonators.
Motivation for the second part of this study stems from the paper manufacturing industry, where air clamp devices utilize high-speed jets to position paper sheets with respect to other equipment. Thus, vibration of the paper sheet and turbulent flow that emerged from a planar curved nozzle between a flexible wall and a solid surface containing a backward-facing step (BFS) were investigated using high-speed photography and DPIV, respectively. The emphasis was on the characterization of the flow physics in the air clamp device, as well as of the shape of the paper sheet. For the control case, that involved a solid wall with a geometry that represented the time-averaged paper profile, hydrodynamic oscillation frequencies were characterized using unsteady pressure measurements. Experimentally obtained frequencies of the paper sheet vibration were compared to the hydrodynamic frequencies corresponding to the oscillations of the shear layer downstream of the BFS.
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Quiescent and flow-induced crystallization of poly(lactic acid) / La cristallisation statique et induite par écoulement du poly(acide lactique)Jalali, Amirjalal January 2017 (has links)
Le poly(acide lactique), PLA, est un polymère biocompatible et biodégradable, qui peut être
produit à partir de ressources renouvelables. En conséquence, il a soulevé une attention toute
particulière en tant que remplacement éventuel des polymères à base de pétrole. C’est un
polyester aliphatique ayant des propriétés telles que module élevé, haute résistance,
biocompatibilité et est donc un matériau prometteur pour diverses applications telles que les
implants, l’encapsulation de médicaments et l'emballage. A cause de sa faible température de
transition vitreuse, le PLA a une faible résistance thermique et les applications sont donc
limitées à celles qui ne sont pas associées à des températures élevées. En outre, ce polymère
souffre d'un faible degré de cristallinité. L'augmentation du taux de cristallinité dans de
nombreuses techniques de mise en forme, telles que le moulage par injection, est nécessaire.
Il y a plusieurs façons d'augmenter le niveau de cristallinité du PLA. Ces procédés
comprennent l'utilisation d'agents nucléants, de plastifiants, ou de combinaisons d'agents
plastifiants et de nucléation. La cristallisation du PLA à l'état fondu se présente sous deux
formes cristallines légèrement différentes connues sous les noms α et α'. Cette étude compare
la capacité d'auto-nucléation de ces deux formes cristallines par auto-nucléation. Ceci est
réalisé en comparant les températures de cristallisation lors du refroidissement des
échantillons préalablement cristallisés à diverses températures, puis de nouveau chauffé à une
température dans la plage de fusion partielle du PLA. Dans la deuxième étape, l'effet des
paramètres cinétiques et le poids moléculaire du PLA sur l'efficacité de nucléation des PLA
phases cristallines a été étudié. Cette partie de l’étude ouvre une nouvelle voie pour
comprendre le rôle des modifications cristallines du PLA qui mènent aux conditions optimales
pour la cristallisation du PLA. La mise en forme des polymères implique des contraintes de
cisaillement et d’élongation, ce qui implique une cristallisation induite par l’écoulement et la
solidification qui s’en suit. Les propriétés mécaniques des produits finals dépendent du degré
de cristallisation et de la nature des cristaux formés. Par conséquent, l'optimisation du procédé
nécessite une bonne compréhension de la façon dont l’écoulement influence la cristallisation.
Le type d'écoulement peut jouer un rôle important sur la cristallisation. Par exemple,
l'écoulement élongationnel provoque l’orientation et l’étirement des molécules dans le sens de
l'extension, comme dans le cas de la mise en forme de fibres et le soufflage de film, en aidant
le processus de cristallisation induite par l'écoulement. Une littérature abondante existe sur la
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cristallisation des thermoplastiques classiques induite par l'écoulement. Cela dit, moins
d'attention a été accordée à l'effet de l'écoulement de cisaillement et d'allongement sur la
cristallisation du PLA. Comme étudié dans la dernière partie de ce document, l'effet du poids
moléculaire sur la cristallisation induite par cisaillement du PLA est rapporté. Pour cela, trois
différents PLA à faible, moyen et haut poids moléculaire ont été préparés par réaction
d'hydrolyse. Ensuite, en utilisant un rhéomètre oscillatoire, l’effet du cisaillement sur la
cinétique de cristallisation du PLA a été examiné. / Abstract : Poly(lactic acid), PLA, is a biocompatible and biodegradable polymer that can be produced
from renewable resources. As a result, it has raised particular attention as a potential
replacement for petroleum-based polymers. It is an aliphatic polyester with properties such as
high modulus, high strength, and biocompatibility and is thus a promising material for various
applications such as implants, drug encapsulation, and packaging. In the wake of low glass
transition temperature, PLA has a low heat resistance and its application is limited to those not
associated with high temperatures. In addition, this polymer suffers from a low degree of
crystalinity. Increasing the crystallization rate in many processing operations, such as injection
molding, is required.
So far, many routes have been found to improve the crystallinity of PLA. These methods
include using nucleating agents, plasticizers, and combination of nucleating agents and
plasticizers together. PLA crystallization in the melt state results in two slightly different
crystalline forms known as α and α’forms. This thesis compares the self-nucleation ability of
these two crystal forms by self-nucleation. This is achieved by comparing crystallization
temperatures upon cooling for samples previously crystallized at various temperatures and
then re-heated to a temperature in the partial melting range for PLA. In the second step, we
study the effect of molecular weight of PLA on the nucleation efficiency of PLA crystalline
phases. This part of the investigation opens a new pathway to understand the role of PLA
crystalline phases on the optimal condition for its crystallization kinetics.
Polymer processing operations involve mixed shear and elongational flows and cause polymer
molecules to experience flow-induced crystallization during flow and subsequent
solidification. The mechanical properties of the final products are significantly dependent
upon the degree of crystallization and types of formed crystals. Therefore, optimization of any
polymer process requires a good understanding of how flow influences crystallization. The
type of flow can play a significant role in affecting crystallization. For example, elongational
flow causes molecules to orient and stretch in the direction of extension, as in the case of fiber
spinning and film blowing, helping the process of flow-induced crystallization. An extensive
body of literature exists on flow-induced crystallization of conventional thermoplastics.
Having said that, less attention has been paid to the effect of shear and elongational flow on
the PLA crystallization kinetics. As investigated in the final part of this thesis, the effect of
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molecular weight on the shear-induced crystallization of PLA is reported. For this, low,
medium and high molecular-weight PLAs were prepared from a high molecular weight one by
a hydrolysis reaction. Next, by means of a simple rotational rheometry, effect of the shear flow
was examined on the crystallization kinetics of these three PLAs.
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Experimental Study of Flow Past a Circular Cylinder with a Flexible Splitter PlateShukla, Sanjay Kumar January 2017 (has links) (PDF)
A circular cylinder is a geometrically simple bluff body that occurs in various practical applications. As with any bluff body, it exhibits large drag forces and a strong fluctuating lift force, both related to the strong shedding of vortices from the body, which is commonly referred to as the Karman Street. Rigid splitter plates in the wake of the cylinder are known to suppress shedding from the body, and thereby result in reduced drag and fluctuating lift forces, the latter being important to reduce flow-induced vibrations of the body. In the present work, the flow past a cylinder with a downstream flexible splitter plate/flap is studied, the length (L) and flexural rigidity (EI) of the flap being the main parameters besides the flow speed (U). Two flaps length to cylinder diameter ratios (L/D), namely, a short (L/D = 2) and a long (L/D = 5) flaps have been studied, the shorter one being smaller than the recirculation zone, while the larger is longer than the recirculation zone. In both these cases, the flexural rigidity (EI) and the flow speed are systematically varied. In all cases, the flaps motion are directly visualized, the lift and drag forces are measured with a force balance, and the wake velocity field is measured using PIV.
In both the long and short flaps cases, the flexural rigidity (EI) of the flexible flap has been varied over a large range of values, and it has been found that the results for flaps tip motion and forces collapse well when plotted with a non-dimensional bending stiffness (K∗), which is defined as K∗ = EI/(1/2ρU2L3). This collapse occurs across flexible flaps with different values of EI, as long as Re > 5000. The collapse is not found to be good for Re < 5000. This difference appears to be related to the large reduction in fluctuating lift for a bare cylinder in the Re range between approximately 1600 and 5000 discussed by Norberg[41].
In the long flap case, the existence of two types of periodic modes is found within the range of K∗ values from 5 × 10−6 to 1 × 10−1 studied. The first one corresponds to a local peak in amplitude at K∗ ≈ 1.5 × 10−3 that is referred to as mode I, and the second that occurs at low values of K∗ (K∗ < 3 × 10−5) that is referred to as mode II. The fluctuating lift is found to be minimum for the mode I oscillation. The mean drag is also found to reach a broad minimum that starts at K∗ corresponding to mode I and continues to be at the same low level of approximately 65% of the bare cylinder drag for all higher K∗ values, representing an approximately 35% decrease in mean drag of the cylinder. The wake measurements also show significant changes with K∗. The formation length (lf /D) obtained from the closure point of the mean separation bubble is found to continuously increase with K∗, reaching values of approximately 2.6 at mode I and thereafter only small increases are seen as K∗ is increased to large values corresponding to the rigid splitter plate case, consistent with the observed variations in the mean drag. The stream wise and cross-stream turbulent intensities and the Reynolds shear stress are all found to be strikingly lower in the mode I case compared to the bare cylinder case, and more importantly, these values are even lower than the rigid splitter plate case. This is consistent with the shedding of weaker vortices and with the minimum in fluctuating lift found in the mode I case. The results for this flap length show that the mode I flap oscillation, corresponding to K∗ ≈ 1.5 × 10−3, may be useful to reduce lift, drag, velocity fluctuations in the wake and the strength of the shed vortices. In particular, the wake fluctuations corresponding to this mode are found to be significantly lower than the rigid splitter plate case.
In the short flap case (L/D = 2), it is found that there exists a richer set of flapping modes compared to the long flap, with these modes being dependent on K∗. At low K∗ values, the flap exhibits large amplitude symmetric flap motion that is referred to as mode A, while clearly asymmetric flaps motion are seen at higher K∗ values corresponding to modes B and C. Mode B corresponds to asymmetric large amplitude flapping motion, while mode C is also asymmetric with the flap clearly deflected off to one side, but
having small oscillation amplitudes. At even higher K∗ values, corresponding to mode D, symmetric flaps motion are again seen with the amplitudes being smaller than in mode A. Apart from the flap tip amplitude, the non-dimensional frequency of flap tip motion also changes as the flap changes modes. In this case, there is a minimum in the fluctuating lift corresponding to mode B and C oscillation. The mean drag is found to reach a minimum again corresponding to mode C, which corresponds to an approximately 35% decrease in mean drag of the cylinder. In this case, there is a large increase in fluctuating lift (approximately 150% of the bare cylinder case) at higher values of K∗ that appears to correspond to a “resonant” condition between the structural natural frequency of the flexible splitter plate/flap and the wake shedding frequency of the bare cylinder. The wake measurements show that the formation length (lf /D) is the largest for mode C (deflected flap state), which is consistent with the observed minimum in mean drag observed for this mode. The stream wise and cross-stream turbulent intensities and the Reynolds shear stress are all found to be strikingly lower in the mode C case compared to the bare cylinder case, with the values for the Reynolds shear stress being lower than the rigid splitter plate case. This is again consistent with the minimum in fluctuating lift found in the mode C case. The results for this flap length show that the mode C flap oscillation, corresponding to K∗ ≈ 5 × 10−2 that correspond to a deflected flap state with very small oscillation may be useful to reduce lift, drag, velocity fluctuations in the wake and the strength of the shed vortices.
The results from the present study show that the flexible flap/splitter plate down-stream of the cylinder exhibits a variety of mode shapes depending on the effective bending rigidity of the flap K∗ for both the long and short flaps cases. The forces and the wake are also found to be strongly dependent on this parameter K∗ with the wake fluctuations, lift fluctuations and the drag being very effectively suppressed at an intermediate value of K∗ that is found to be dependent on the plate/flap length.
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The Dynamics of Viscoelastic Wormlike Micelles in Complex FlowsMoss, Geoffrey R 01 January 2009 (has links) (PDF)
Solutions of self-assembled wormlike micelles are used with ever increasing frequency in a multitude of consumer products ranging from cosmetic to industrial applications. Owing to the wide range of applications, flows of interest are often complex in nature; exhibiting both extensional and shear regions that can make modeling and prediction both challenging and valuable. Adding to the complexity, the micellar dynamics are continually changing, resulting in a number of interesting phenomena, such as shear banding and extensional flow instabilities. Presented in this thesis are the results of an investigation into the flow fields generated by both a controllable and idealized porous media, effected as a periodic array of cylinders as well as a single circular cylinder. In order to fully characterize the kinematics, two rheologically documented test fluids were used. The first test channel geometry consists of six equally spaced cylinders, arranged perpendicular to the flow, while the second consists of a single circular cylinder. By systematically varying the Deborah number, the flow kinematics, stability and pressure drop were measured. A combination of particle image velocimetry in conjunction with flush mount pressure transducers were used to characterize the flow, while flow induced birefringence measurements were used to determine micelle deformation and alignment. In the periodic geometry, the pressure drop was found to decrease initially due to the shear thinning of the test fluid, and then exhibit a dramatic upturn as other elastic effects begin to dominate in one of the test fluids. In the case of the single cylinder, no such upturn was observed. Presented is evidence of the onset of an elastic instability in one of the test fluids above a critical Deborah number, manifest in fluctuating transient pressure drop measurements and asymmetric streamlines. This instability was observed in both test geometries. It is argued that this instability can be attributed to the measurable differences in the extensional rheology of the two fluids.
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Influence of Supraglottal Geometry and Modeling Choices on the Flow-Induced Vibration of a Computational Vocal Fold ModelShurtz, Timothy E. 28 November 2011 (has links) (PDF)
Computational models of the flow-induced vibrations of the vocal folds are powerful tools that can be used in conjunction with physical experiments to better understand voice production. This thesis research has been performed to contribute to the understanding of vocal fold dynamics as well as several aspects of computational modeling of the vocal folds. In particular, the effects of supraglottal geometry have been analyzed using a computational model of the vocal folds and laryngeal airway. In addition, three important computational modeling parameters (contact line location, Poisson's ratio, and symmetry assumptions) have been systematically varied to determine their influence on model output. Variations in model response were quantified by comparing glottal width, frequency, flow rate, open quotient, pressures, and wave velocity measures. In addition, the glottal jet was qualitatively analyzed. It was found that for various supraglottal geometries (either symmetrically or asymmetrically positioned), there was little asymmetry of the vocal fold motion despite significant asymmetry in the glottal jet. In addition, the vocal fold motion was most symmetric when consistent jet deflection was present (even if asymmetric). Inconsistent deflection of the glottal jet led to slightly larger asymmetries in vocal fold motion. The contact line location was found to have minimal impact on glottal width, frequency, and flow rate. The largest influence of the contact line location was seen in predicted velocity fields during the closed phase and in the pressure profiles along the vocal fold surfaces. Variations in Poisson's ratio strongly affected vocal fold motion, with lower Poisson's ratios resulting in larger amplitudes. The model did not vibrate when a Poisson's ratio of 0.49999 was used. The response of a full model (with two vocal folds) was shown to vary slightly from that of a half model (one vocal fold and a symmetry boundary condition), the greatest difference being in the deflection and dissipation of the glottal jet. It was concluded that for many scenarios the half model will be sufficient for modeling vocal fold motion; however, a full model is suggested for studies of material asymmetry or glottal jet dynamics. Application of these results to computational models of the vocal folds will lead to improved modeling and understanding of vocal fold dynamics.
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FLOW INDUCED VIBRATIONS IN PIPES, A FINITE ELEMENT APPROACHGRANT, IVAN 25 May 2010 (has links)
No description available.
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Flow-Induced Noise of Perforated Plates at Oblique Angles of IncidenceVanoostveen, Paul 11 1900 (has links)
In this thesis, the tonal noise produced by flow over perforated plates at oblique angles of incidence is studied experimentally. A two-dimensional model of a perforated plate is used, where the circular holes of a typical perforated plate are replaced by a series of long rectangular Aluminum slats with an adjustable gap width between them. The slats are 3.175 mm thick and the gap width between them is set to 3.175 mm, 6.35 mm, and 12.7 mm. This simplified model is mounted at the exit of an open-loop wind tunnel and tested at angles of incidence of 0° to 40° and flow velocities of 0 to 30 m/s. An angle of 0° is defined as flow parallel to the plate. The acoustic response is studied using microphone measurements, and flow visualization is done using particle image velocimetry. The effect of the angle of incidence, flow velocity, gap width, and streamwise position are investigated. The flow visualization reveals that tonal noise is produced by the periodic shedding and impingement of vortices at the trailing edge of the gaps. Vortices form in the unstable free shear layer originating at the leading edge of the gap and impinge on the downstream side of the gap. At the downstream corner, these vortices separate into vortex pairs, consisting of one positively rotating and one negatively rotating vortex. These vortices are shed periodically, leading to the production of tonal noise at the shedding frequency. The effect of the angle of incidence is investigated by changing the angle of the plate with respect to the flow. For a given gap width, tones are produced only for a specific range of angles. Depending on the plate geometry, this range of angles is typically around 5° to 30°. Within this range of angles, the free shear layer impinges on the downstream side of the gap. For angles which are too small or too large, the free shear layer misses this downstream side and tones are not produced. For a larger gap width, tones are produced at smaller angles of incidence. Similarly, for a given plate geometry, there is a preferred range of flow velocities at which tonal noise is produced. The velocity at which the free shear layer is the most unstable at the tone frequency produces the strongest vortices and the loudest tones. The optimal velocity is lower for larger gap widths. Finally, it is found that the magnitude of the produced tones increases in the streamwise direction over repeated gaps along the length of the plate. This is due to the local flow conditions changing in the streamwise direction, only reaching the optimal conditions after a certain length of the plate. / Thesis / Master of Applied Science (MASc)
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Characterization of Fluid Structure Interaction mechanisms and its application to vibroacoustic phenomenaQuintero Igeño, Pedro Manuel 15 October 2019 (has links)
[ES] La Interacción Fluido Estructura consiste en un problema físico en el
que dos materiales, gobernados por conjuntos de ecuaciones distintas, se
acoplan de diferentes formas.
La investigación en el campo de la Interacción Fluido Esructura
experimentó un importante desarrollo desde principios del siglo XX, de la
mano del campo de la aeroelasticdad. Durante el desarrollo de la industria
aeroespacial en el contexto de las guerras mundiales, el uso de materiales
más ligeros (y flexibles) comenzó a hacerse obligatorio para la obtención de
aeronaves con un comportamiento (y costes) aceptable.
A lo largo de los últimos años, el uso de materiales de construcción
cada vez más ligeros, se ha extendido al resto de campos de la industria.
A modo de ejemplo, podría servir el desarrollo de trackers en la producción
de energia solar; la utilización de materiales ligeros en ingeniería
civil o el desarrollo de elementos constructivos de plástico en la industria
del automóvil. Como consecuencia, la predicción con exactitud de las
deformaciones inducidas por un fluido y, si aplica, la influencia de estas
deformaciones en el propio flujo, ha adquirido una importancia vital.
Este documento intenta porporcionar, en primer lugar, una profunda
revisión de los métodos experimentales y computacionales que se han utilizado
en este contexto en la bibliografía, así como los análisis en problemas
de este tipo realizados por otros investigadores de cara a presentar una
primera aproximación a la Interacción Fluido Estructura.
Se verá cómo existe una importante cantidad de herramientas y
metodologías aplicables a cualquier tipo de problema y para cualquier
combinación de flujos y estructuras. Sin embargo, no existe una aproximación
general que, en función de valores de números adimensionales,
permita establecer cuáles de ellos son los de mayor importancia en este
tipo de problemas. En este sentido, se llevará a cabo un completo análisis
paramétrico durante el desarrollo del Capítulo 2 para establecer cuáles de
ellos son de mayor importancia.
Una vez se establezca la importancia de estos parámetros, se analizará
un caso que es de especial interés en la industria: la aerovibroacústica. Éste
es un caso particular de Interacción Fluido Estructura en el que, debido a
la combinación de parámetros adimensionales, la interacción se puede considerar
como prácticamente unidireccional, permitiendo extender estudios
mediante un conste computacional relativamente acotado. La Aerovibroacústica
y la vibroacústica se analizarán mediante la presentación de
dos casos de referencia, permitiendo proponer una metodología que se
podrá extender a otros problemas similares. / [CA] La Interacció Fluid Estructura consisteix en un problema físic en què
dos materials, governats per conjunts d'equacions diferents, s'acoblen de
diferents formes.
La investigació en el camp de la Interacció Fluid Esructura va experimentar
un important desenvolupament des de principis del segle XX,
de la mà del camp de la aeroelasticdad. Durant el desenvolupament de
la indústria aeroespacial en el context de les guerres mundials, l'ús de
materials més lleugers (i flexibles) va començar a fer-se obligatori per a
l'obtenció d'aeronaus amb un comportament (i costos) acceptable.
Al llarg dels últims anys, l'ús de materials de construcció cada vegada
més lleugers, s'ha estès a la resta de camps de la indústria. A tall
d'exemple, podria servir el desenvolupament de textit trackers en la producció
d'energia solar; la utilització de materials lleugers en enginyeria
civil, el desenvolupament d'elements constructius de plàstic a la indústria
de l'automòbil. Com a conseqüència, la predicció amb exactitud de les
deformacions induïdes per un fluid i, si escau, la influència d'aquestes
deformacions en el propi flux, ha adquirit una importància vital.
Aquest document intenta porporcionar, en primer lloc, una profunda
revisió dels mètodes experimentals i computacionals que s'han utilitzat
en aquest context en la bibliografia, així com les anàlisis en problemes
d'aquest tipus realitzats per altres investigadors de cara a presentar una
primera aproximació a la Interacció Fluid Estructura.
Es veurà com, encara que existeix una important quantitat d'eines
i metodologies aplicables a qualsevol tipus de problema i per a qualsevol
combinació de fluxos i estructures, no hi ha una aproximació general que,
en funció de valors de nombres adimensionals, permeti establir quins
d'ells són els de major importància en aquest tipus de problemes. En
aquest sentit, es durà a terme una completa anàlisi paramètric durant
el desenvolupament del Capítol 2 per a establir quins d'ells són de major
importància.
Un cop s'estableixi la importància d'aquests paràmetres, s'analitzarà
un cas que és d'especial interès en la indústria: la aerovibroacústica. Això
és un cas particular d'Interacció Fluid Estructura en què, a causa de la
combinació de paràmetres adimensionals, la interacció es pot considerar
com pràcticament unidireccional, permetent estendre estudis mitjançant
un consti computacional relativament acotat. La Aerovibroacústica i la
vibroacústica s'analitzaran mitjançant la presentació de dos casos de referència,
permetent proposar una metodologia que es podrà estendre a altres
problemes similars. / [EN] Fluid Structure Interaction is a physical problem where two different
materials, governed by different set of fundamental equation, are coupled
on different ways.
The research on the field of Fluid Structure Interaction experienced
a noticeable growth since the beginnings of the XXth century, by means
of the field of aeroelasticity. During the development of the aerospace
industry in the context of first and second Wolrd War, as the use of lighter
(and softer) materials became mandatory for the correct behavior (and cost
savings) of the produced aircrafts.
During these past years, the use of use of increasingly lighter construction
materials has extended to the rest of fields of the industry. As an
example, it could be mentioned the use of solar trackers on the solar energy
sector; the use of light materials on civil engineering or the use of plastic
for some constructive elements in the context of the automotive field. As a
consequence, the accurate prediction of the deformations induced to a fluid
flow over a structure and, if needed, the influence of this deformation on
the fluid flow itself is becoming of primal importance.
This document intends to provide with a deep review of the computational
and experimental reported methodologies already available on the
literature and the previous works performed by other researches in order
to infer a first approximation to the Fluid Structure Interaction Problem.
It will be observed how an important amount of solving methodologies
is available in order to face these problems regarding with the strength
of the interaction. However, a general approximation allowing to predict
this strength as a function of a set of dimensional number is rarely
known. In this sense, a full parametric study will be performed during the
development of Chapter 2 showing which of them are of higher importance.
Once the influence of these parameters is determined, a case of special
interest will be analyzed: aerovibroacoustics. This, is a particular case
of Fluid Structure Interaction where, due to the combination of its nondimensional
parameters, one directional coupling can be supposed for most
of the cases. Aerovibroacoustics and vibroacoustics will be analyzed by
means of two reference cases, allowing finally to propose a methodology
which could be extended for other related problems. / Quintero Igeño, PM. (2019). Characterization of Fluid Structure Interaction mechanisms and its application to vibroacoustic phenomena [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/128412
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Investigation et application des méthodes d'ordre réduit pour les calculs d'écoulements dans les faisceaux tubulaires d'échangeurs de chaleur / Investigation and application of reduced-order methods for flows study in heat exchanger tube bundlesPomarède, Marie 07 February 2012 (has links)
Cette thèse s’intéresse à la faisabilité de la mise en place de modèles d’ordre réduit pour l’étude des vibrations sous écoulement au sein de faisceaux tubulaires d’échangeurs de chaleur. Ces problématiques sont cruciales car les systèmes étudiés sont des éléments majeurs des centrales nucléaires civiles et des chaufferies embarquées dans les sous-marins.Après avoir rappelé le fonctionnement et les risques vibratoires existants au sein des échangeurs de chaleur, des calculs complets d’écoulement et de vibrations sous écoulement ont été effectués, d’abord pour un tube seul en milieu infini, puis pour un faisceau de tubes. Ces calculs ont été menés avec l’outil CFD Code_Saturne. La méthode de réduction de modèle POD (Proper Orthogonal De-composition) a été appliquée au cas des écoulements avec la structure laissée fixe.Les résultats obtenus montrent l’efficacité de la méthode pour ces configurations, moyennant l’introduction de méthodes de stabilisation pour l’écoulement au sein du faisceau. La méthode POD-multiphasique, permettant d’adapter la méthode POD à l’interaction fluide-structure, a ensuite été appliquée. Les grands déplacements d’un cylindre seul dans la zone d’accrochage (lock-in) ont été correctement reproduits par cette méthode de réduction de modèle. De même, on montre que les grands déplacements d’un cylindre en milieu confiné dans un faisceau de tubes sont fidèlement reconstruits.Enfin, l’extension de l’utilisation de la réduction de modèle aux études d’évolution paramétrique a été testée. Nous avons d’abord utilisé la technique considérant une base POD unique pour reproduire des écoulements à divers nombres de Reynolds autour d’un cylindre seul. Les résultats confirment la prédictivité bornée à une gamme de paramètres de cette méthode. Enfin, l’interpolation de bases POD pré-calculées pour une famille de paramètres donnés, utilisant les variétés de Grassmann et permettant de générer de nouvelles bases POD, a été testée sur des cas modèles. / The objective of this thesis is to study the ability of model reduction for investigations of flow-induced vibrations in heat exchangers tube bundle systems.These mechanisms are a cause of major concern because heat exchangers are key elements of nuclear power plants and on-board stoke-holds.In a first part, we give a recall on heat exchangers functioning and on vi-bratory problems to which they are prone. Then, complete calculations leaded with the CFD numerical code Code_Saturne are carried out, first for the flow around a single circular cylinder (fixed then elastically mounted) and then for the case of a tube bundle system submitted to cross-flow. Reduced-order method POD is ap-plied to the flow resolution with fixed structures. The obtained results show the efficiency of this technique for such configurations, using stabilization methods for the dynamical system resolution in the tube-bundle case.Multiphase-POD, which is a method enabling the adaptation of POD to fluid-structure interactions, is applied. Large displacements of a single cylinder elastically mounted under cross-flow, corresponding to the lock-in phenomenon,are well reproduced with this reduction technique. In the same way, large displace-ments of a confined moving tube in a bundle are shown to be faithfully recon-structed.Finally, the use of model reduction is extended to parametric studies. First,we propose to use the method which consists in projecting Navier-Stokes equations for several values of the Reynolds number on to a unique POD basis. The resultsobtained confirm the fact that POD predictability is limited to a range of parameter values. Then, a basis interpolation method, constructed using Grassmann mani-folds and allowing the construction of a POD basis from other pre-calculated basis,is applied to basic cases.
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Étude des sollicitations dynamiques induites par un fluide lourd au passage d'une singularité / Study of the dynamic excitation induced by dense fluids flowing through piping singularitiesBaramili Fleury De Amorim, André 20 December 2017 (has links)
Les réseaux de tuyauterie industriels sont le siège de niveaux importants de vibrations induites par l’écoulement qui peuvent mener à la rupture par fatigue des installations. La présente étude se concentre sur l’analyse et modélisation simplifiée de la source vibratoire associée au passage d’un écoulement liquide turbulent par un coude à 90°. Une approche combinant expériences et simulation a été conduite. Une boucle de circulation d’eau munie d’un coude transparent a été conçue afin de permettre des me-sures de vitesse à l’intérieur du coude. Pour cette finalité, les techniques de Vélocimétrie par Imagerie de Particules (PIV) plane et stéréoscopique ont été utilisées. La pression pariétale et les vibrations du banc d’essais ont été mesurées simultanément. Plusieurs configurations d’écoulement ont été testées afin d’obtenir une riche base de données couplées reliant l’écoulement fluide à l’excitation dynamique des parois et, finalement, à la réponse vibratoire de la structure. En parallèle, l’écoulement instationnaire d’eau dans le coude a été simulé au moyen d’une approche du type Simulation des Grandes Echelles (LES). La simulation fluide a permis d’étudier en détails la topologie de l’écoulement turbulent au passage du coude ainsi que le champ instationnaire de pression fluctuante induit sur la paroi. Finale-ment, un ensemble d’outils statistiques a été appliqué aux données expérimentales et numériques afin de proposer un modèle simplifié des transferts qui relient l’écoulement turbulent à la sollicitation dynamique de la structure contenant le coude. / The flow of dense fluids within thin-walled piping systems may lead to significant levels of Flow-Induced Vibration, mainly in the vicinities of singularities such as obstacles inserted into the flow, sudden changes of cross-sectional area or flow direction. This study focuses on the analysis and reduced-order modelling of the vibrational source associated with the turbulent flow of liquids through a 90° elbow.A mixed experimental-computational approach is undertaken. A closed water loop containing a transparent elbow was designed in order to allow for fluid velocity measurements inside the singularity. To this purpose, planar and stereoscopic Particle Image Velocimetry (PIV) were employed. Wall pressure fluctuations and structural vibrations were measured simultaneously. Several flow configurations were tested in order to obtain a large coupled database linking the flow to the dynamic excitation, and then to the vibration response of the structure.In parallel, the unsteady water flow through the elbow was computed using Large-Eddy Simulation (LES). The fluid simulation allowed for a detailed study of the turbulent flow through the singularity and the unsteady pressure field induced on the piping walls. Finally, a set of statistical tools was applied to both experimental and computational data in order to propose a reduced-order model of the transfer function that links the tur-bulent flow to the dynamic excitation of the elbowed piping structure.
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