Добірка наукової літератури з теми "Cylinder bundles"

Self-excited acoustic resonance is a design concern in many engineering applications such as tube bundles of heat exchangers and boilers. Since this phenomenon is not yet fully understood, it can be dangerously unpredictable. Due to the complexity of the flow-sound interaction mechanisms in tube bundles, the simplified cases of a single cylinder and two cylinders in various arrangements, tandem and staggered, are investigated in some detail. A summary of these investigations is presented in the current paper. It is found that the aeroacoustic response of two-tandem and side-by-side cylinders in cross-flow can be considerably different from that of a single cylinder under similar flow conditions. Moreover, for the case of two tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity; the pre-coincidence and the coincidence resonance ranges. The pre-coincidence acoustic resonance phenomenon is found to be similar to the acoustic resonance mechanism of in-line tube bundles.

The vascular system of the sessile, fertile spikelet of Sorghum was reconstructed from serial transverse sections. The vascular system is a composite of the basipetal extensions of the traces from the appendages on the rachilla. The rachilla immediately above the glumes consists of an outer and an inner series of these vascular extensions. The basipetal continuations of the median traces of the sterile and fertile lemmas, and of the traces from the stamens comprise the inner series. The outer series consists of the continuations of the many lodicule traces and of vascular bundles descending from the posterior of the pistil. The component of the vascular system related to the pistil is a plexus of xylem and phloem in the form of a hollow cylinder traversed by a large vascular bundle that is the basipetal continuation of the stylar bundles. Bundles from the anterior of the pistil merge with the hollow cylinder at its anterior. Several collateral bundles from the placenta merge with the hollow cylinder at its posterior. Distal portions of these placental bundles supply the short chalaza of the ovule but do not enter it. The vascular system of the fertile spikelet of Sorghum is typical of the Panicoideae, and is useful in distinguishing the Panicoideae from the other subfamilies of grasses. Key words: Sorghum, spikelet, floret, vascular system.

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures over a broad range of void fraction and mass fluxes. Both the dynamic lift and drag forces were measured with strain gage instrumented cylinders. The experiments revealed somewhat unexpected but significant quasi-periodic forces in both the drag and lift directions. The periodic forces appeared well correlated along the cylinder with the drag force somewhat better correlated than the lift forces. The periodic forces are also dependent on the position of the cylinder within the bundle.

In Cordyline indivisa Kunth, an anatomical modification occurs in the primary bundles, in relation to the pattern of their longitudinal course. Consequently, in a given transverse section of the stem, the bundles may be in different structural stages (collateral, intermediate types 1 and 2, amphivasal). All the procambial or primary vascular bundles in the upper 8.59 mm of the stem of an 18-month-old plant were recorded. At regular intervals below the apex, the numbers and percentages of bundles showing each of the structural stages were also recorded. Based on the pattern of bundle construction previously shown for this species, the constitution of the primary cylinder at various distances below the apex is explained in relation to the distribution of the different structural stages.

In all three investigated cultivars, the thin part of the peduncle which originates from the inflorescence axes contained a continuous cylinder of vascular tissue interrupted only occasionally by the gaps accompanying the traces of already abscised ramifications of the inflorescence. In the cvs. Principe Negro and Fuerte, the most distal, "thick" part of the peduncle (where the tepal traces separate) contained the vascular cylinder transformed into a group of concentric or semicircular bundles. These bundles joined anew at the point where the peduncle united with the fruit, forming once more a continuous cylinder of vascular tissues. Within the fruit, the vascular cylinder divided into numerous bundles penetrating the pulp. In cv. Hass the vascular cylinder was continuous in a11 parts of the peduncle, and was interrupted only occasionally by gaps.

The purpose of this article is to present fire and explosion properties of acetylene, the requirements for storing and transporting this gas, and to present the results of tests conducted on single acetylene cylinders and on cylinder bundles. Hazardous area coverage during rescue operations involving acetylene cylinders in open areas should be at least 300 m. Care must be taken when handling rescue operations and all available safety measures should be used.

Дисертаційна робота присвячена дослідженню теплогідравлічних процесів навколо циліндричних поверхонь теплообміну в залежності від зміни режимних параметрів процесу та конструктивних характеристик оточення. В роботі представлено результати візуалізації динамічного поля та поля температури теплоносія, що дозволило значно поглибити знання про механізми тепло- та масопереносу та більш обґрунтовано описати результати дослідження. Отримані результати дослідження дозволили, в діапазоні зміни режимних та конструктивних характеристик, описати вплив цих факторів на коефіцієнти тепловіддачі та характеристики омивання циліндрів, і вивести залежності для розрахунку коефіцієнтів тепловіддачі з врахуванням виявленого впливу.
In the investigation are developed heat and mass transfer theory around horizontal cylinders which depends on heat flux and several constructive characteristics: presents or absence of vertical walls, other horizontal cylinders placed close to each other. Results of dynamic and temperature field visualization are also presented. These results made our knowledge significantly deeper in a part of heat and mass transfer mechanism during natural convection around cylinder systems. Cylinder, placed inside a vertical channel, has variable heat transfer coefficient, which depend on channel geometrical characteristic. If a cylinder will be placed inside the channel with optimal characteristic, its heat transfer coefficient will be increased around 20%. These optimal width is 2,2-2,3 cylinder diameter. Heat transfer coefficient of cylinder bundl is deeply depends on its constructive characteristic. Based on obtained results, formulas and calculation algoritm of heat transfer coefficient was developed, take into consideration several variables.
Диссертационная работа посвящена исследованию теплогидравлических процессов вокруг цилиндрических поверхностей теплообмена в зависимости от изменения режимных параметров процесса и конструктивных характеристик окружения: наличия адиабатных стенок канала, соседних цилиндров в горизонтальном и/или вертикальном направлениях. В работе представлены результаты визуализации динамического поля и поля температуры теплоносителя, которые позволили значительно углубить знания о механизмах тепло- и массопереноса, более точно и обосновано описать изучаемые процессы и результаты исследования. Кроме этого, проведення работа по визуализации исследуемых процессов разрешила проявить коренные изменения в динамическом поле вокруг горизонтального цилиндра (в частности, при его размещении в вертикальном канале), развитию теплового следа над цилиндром в большом объеме, в и над системой цилиндров. Полученные результаты исследования позволили, в изученном диапазоне изменения режимных и конструктивных характеристик, описать влияние этих факторов на коэффициенты теплоотдачи и характеристики движения теплоносителя вокруг системы цилиндров, вывести зависимости для расчета коэффициентов теплоотдачи с учетом такого влияния. В частности показано, что при размещении горизонтального цилиндра в вертикальном щелевидном канале возможно значительное изменение условий течения теплоносителя, что, в свою очередь, может приводить как к повышению, так и понижению интенсивности теплоотдачи на поверхности такого цилиндра. Впервые предложена диаграмма теплогидравлических режимов, которая позволяет уже на этапе конструирования теплообменной поверхности и её окружения ответить на вопрос об оптимальности выбранной конструкции. Кроме инженерных методик расчета интенсивности теплоотдачи от цилиндров в различных условиях, в работе представленные рекомендации по проектированию цилиндрических теплообменных поверхностей, которые рассчитаны на работу в условиях свободной конвекции и учитывают вскрытые изменения динамического и температурного полей при изменении конструктивного окружения цилиндров. В частности, среди таких рекомендацый не обходимо выделить следующие: интенсивность теплоотдачи значительно снижается при формировании пучка цилиндров с малими вертикальным и горизонтальным шагом установки элементов системы; при этом, большее значение имеет вертикальный шаг установки цилиндров; интенсивность теплоотдачи от цилиндров пучка равная такой для одиночного горизонтального цилиндра в большом объеме достигается при относительном вертикальном шаге их установки равном 5,0; впервые предложена и обоснована методика разделения системы цилиндров на отдельные группы при расчете локального и среднего коэффициента теплоотдачи, что позволяет учитывать особенности теплогидравлических процессов внутри системы; показано, что интенсивность теплоотдачи от глубинных цилиндров в системе до 11 элементов, устанавливается равной, примерно, среднему значению между интенсивностями теплоотдачи второго и третього цилиндров; интенсивность теплоотдачи вдоль течения теплоносителя сильно зависит от геометрических характеристик системы и может как уменшаться (при малых вертикальних шагах установи цилиндров), так и увеличиваться (при наибольших из исследованных).

This thesis contains measurements of the wall pressure fluctuations on cylinders in a bundle in turbulent axial flow in a cylindrical channel. The measurements were made for the purposes of obtaining insight into the nature of the turbulent pressure field and providing analytical approximations of wall pressure correlations required by a previously derived theory for predicting the flow-induced vibration of cylinders in axial flow.
The turbulent pressure field at the walls of the cylinders is examined in both the frequency and time domains via measured power-spectral densities, cross-spectral densities, auto-correlations and cross-correlations in azimuthal and longitudinal planes in the cylinder bundle over a range of flow velocities. The data is then nondimensionalized to give dimensionless power-spectral densities and azimuthal (or lateral) and longitudinal correlation functions, which are then approximated analytically and compared to a previous analytical approximation for pipe flow. Typical force-per-unit-length spectra are also obtained from the pressure measurements.

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

The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. Condensation heat transfer results are available in ranges from (U&
#61605
= 1 - 30 m/s) for free stream velocity, (m1,&
#61605
= 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T&
#61605
-Tw =10-40 K) for temperature difference. Results show that
a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.

A multitude of processes cooperate to produce the sensation of sound. The key initial step, the transformation from mechanical motion into an electrical signal, takes place in highly specialized mechanosensitive organelles that are called hair bundles due to their characteristic appearance. Each hair bundle comprises many apposed cylindrical stereocilia that are located in a liquid-filled compartment of the inner ear. The viscous liquid surrounding the hair bundle dissipates energy and dampens oscillations, which poses a fundamental physical challenge to the high sensitivity and sharp frequency selectivity of hearing. To understand the structure-function relationship in this complex system, a realistic physical model of the hair bundle with an appropriate representation of the fluid-structure interactions is needed to identify the relevant physical effects. In this work a novel approach is introduced to analyze the mechanics of the fluid-structure interaction problem in the inner ear. Because the motions during normal mechanotransduction are much smaller than the geometrical scales, a unified linear system of equations describes with sufficient accuracy the behavior of the liquid and solid in terms of a displacement variable. The finite-element method is employed to solve this system of partial differential equations. Based on data from the hair bundle of the bullfrog's sacculus, a detailed model is constructed that resolves simultaneously the interaction with the surrounding liquid as well as the coupling liquid in the narrow gaps between the individual stereocilia. The experimental data are from high-resolution interferometric measurements at physiologically relevant amplitudes in the range from a fraction of a nanometer to several tens of nanometers and over a broad range of frequencies from one millihertz to hundred kilohertz. Different modes of motion are analyzed and their induced viscous drag is calculated. The investigation reveals that grouping stereocilia in a bundle dramatically reduces the total drag as compared to the sum of the drags on individual stereocilia moving in isolation. The stereocilia in a hair bundle are interconnected by oblique tip links that transmit the energy in a sound to the mechanotransduction channels and by horizontal top connectors that provide elastic coupling between adjacent stereocilia. During hair-bundle deflections, the tip links induce additional drag by causing small but very dissipative relative motions between stereocilia; this effect is offset by the horizontal top connectors that restrain such relative movements, assuring that the hair bundle moves as a unit and keeping the total drag low. In the model the stiffness of the links, the stiffness of the stereocilia, and the geometry are carefully adjusted to match experimental observations. The references are stiffness and drag measurements, as well as the coherence measurements for the bundle's opposite edges, both with and without the tip links. The results are further validated by a comparison with the relative motions measured in a sinusoidally stimulated bundle for the distortion frequencies at which movements are induced by the nonlinearity imposed by channel gating. The model of the fluid-structure interactions described here provides insight into the key step in the perception of sound and the method presented provides an efficient and reliable approach to fluid-structure interaction problems at small amplitudes
Bei der Hörwahrnehmung eines Klangs spielen viele komplexe Prozesse zusammen. Der Schlüsselprozess, die Umwandlung mechanischer Schwingungsbewegung in elektrische Signale, findet in den Haarbündeln im Innenohr statt. Diese Haarbündel sind hoch entwickelte mechanosensitive Organellen, bestehend aus vielen nahe beieinander stehenden Stereozilien umgeben von Flüssigkeit. Die beträchtliche Viskosität dieser Flüssigkeit führt zur Energiedissipation und zur Schwingungsdämpfung, was im Gegensatz zur bekannten hohen Empfindlichkeit und der ausgezeichneten Frequenzselektivität der Hörwahrnehmung steht. Um die Komponenten des Haarbündelsystems in ihrem funktionalen Zusammenspiel besser zu verstehen, bedarf es eines wirklichkeitsgetreuen Modells unter Einbeziehung der Wechselwirkung zwischen Flüssigkeit und Struktur. Mit dieser Arbeit wird ein neuer Ansatz vorgestellt, um die Mechanik der Fluid-Struktur-Wechselwirkung im Innenohr zu analysieren. Da die Bewegungen bei der normalen Mechanotransduktion wesentlich kleiner als die geometrischen Abmessungen sind, ist es möglich, das Verhalten von Fluid und Struktur in Form der Verschiebungsvariable in einem linearen einheitlichen System von Gleichungen ausreichend genau zu beschreiben. Dieses System von partiellen Differentialgleichungen wird mit der Finite-Elemente-Methode gelöst. Basierend auf experimentell ermittelten Daten vom Haarbündel des Ochsenfrosches wird ein detailliertes Modell erstellt, welches sowohl die Interaktion mit der umgebenden Flüssigkeit als auch die koppelnde Flüssigkeit in den engen Spalten zwischen den einzelnen Stereozilien erfasst. Die experimentellen Daten sind Ergebnisse von hochauflösenden interferometrischen Messungen bei physiologisch relevanten Bewegungsamplituden im Bereich von unter einem Nanometer bis zu mehreren Dutzend Nanometern, sowie über einen breiten Frequenzbereich von einem Millihertz bis hundert Kilohertz. Das Modell erlaubt die Berechnung der auftretenden viskosen Widerstände aus der numerischen Analyse der verschiedenen beobachteten Bewegungsmoden. Es kann gezeigt werden, dass durch die Gruppierung zu einem Bündel der Gesamtwiderstand drastisch reduziert ist, im Vergleich zur Summe der Widerstände einzelner Stereozilien, die sich individuell und unabhängig voneinander bewegen. Die einzelnen Stereozilien in einem Haarbündel sind durch elastische Strukturen mechanisch miteinander verbunden: Die Energie des Schalls wird durch schräg angeordnete sogenannte Tiplinks auf die mechanotransduktiven Kanäle übertragen, wohingegen horizontale Querverbindungen die Stereozilien direkt koppeln. Während der Haarbündelauslenkung verursachen die Tiplinks zusätzlichen Widerstand durch stark dissipative Relativbewegungen zwischen den Stereozilien. Die horizontalen Querverbindungen unterdrücken diese Bewegungen und sind dafür verantwortlich, dass sich das Haarbündel als Einheit bewegt und der Gesamtwiderstand gering bleibt. Die Steifigkeit der Stereozilien und der Verbindungselemente sowie deren Geometrie sind in dem Modell sorgfältig angepasst, um eine Übereinstimmung mit den Beobachtungen aus verschiedenen Experimenten zu erzielen. Als Referenz dienen Steifigkeits- und Widerstandsmessungen, sowie Kohärenzmessungen für die gegenüberliegenden Außenkanten des Bündels, die jeweils mit und ohne Tiplinks durchgeführt wurden. Darüberhinaus sind die Ergebnisse durch den Vergleich mit experimentell beobachteten Relativbewegungen validiert, die das Haarbündel infolge von sinusförmiger Anregung bei Distorsionsfrequenzen zeigt. Diese haben ihren Ursprung in dem nichtlinearen Prozess des öffnens von Ionenkanälen. Das entwickelte Modell eines Haarbündels liefert neue Einblicke in den Schlüsselprozess der auditiven Wahrnehmung. Zur Behandlung von Problemen der Fluid-Struktur-Wechselwirkungen bei kleinen Amplituden hat sich der hier ausgearbeitete Ansatz als effizient und zuverlässig erwiesen

Since the discovery of soccer-ball-shaped C60 (Kroto et al., 1985), fullerenes have been added to the family of allotropes of carbon element. During the fullerene formation by arc-discharge of graphite electrodes, carbon nanotubes were simultaneously grown as a deposit on the electrode (Iijima, 1991). The carbon nanotubes consist of single or multiple graphene sheets rolled in the form of a seamless cylinder, with the diameter of the hollow core being almost 10 Å (similar to that of fullerenes) or even as small as 4 Å. For these new forms of nanometer-sized carbon, so-called nanocarbons, basically similar concepts as GICs have been applied from the aspects of structures, electronic properties, and functionalities that can be controlled by doping or intercalation process. That is, the bonding force between nanoballs or nanotubes is governed by weak van der Waals forces, so that foreign species such as atoms or molecules can be intercalated (or doped) in the van der Waals gaps, similar to graphite. So, from applications and the basic science of these new carbon families, intercalation as well as doping to these hosts has been studied intensively in the last ten years. There are three kinds of doping reactions of guest species into these host materials, which are reflected in their specific structure. Guest atoms can be introduced by substituting the carbon atoms of the hosts. This process is generally called “doping,” as there is a similarity with the doping process in semiconductors, where, in general, there is no long-range periodicity in the guest arrangement against the host crystal. Guests can locate in the hollow cores of fullerenes or carbon nanotubes as well as on their outer surfaces. GICs establish the super-lattice structure between the host of the graphite lattice and the inserted guest species, where the long-range periodicity along the c-axis as well as on the a-b plane is formed. According to the original meaning of “intercalation,” periodic doping to the host materials is defined as intercalation. So, the three kinds of doping are: (1) endohedral doping into the hollow cage; (2) substitutional doping by replacing the carbon atoms on the cages; and (3) exohedral doping where the dopants are sited in the gaps between the cage molecules of a fullerene crystal or between carbon nanotubes in the array of the bundle form.

A new nozzle using a composite flow network has been developed for plain air film stabilization without film break. The design consists of a slit duct with layers of diamond-shaped cylinder bundles. Tests were conducted using air at average velocity of 8m/s. The new nozzle had a stabilized length in its flow direction stretching 2 times, compared to a conventional slit design. The development of new nozzle was based on fluid dynamic theory. A new type of intersecting flow networks, to be referred to as composite flow network, was constructed consisting of ambivalent flows superposed with con-current thin-film flows in diamond-shaped cylinder bundles. Our previous experiments have revealed the occurrence of flip-flop flow with self-sustained flow oscillations and the generation of longitudinal vortices in the diamond-shaped cylinder bundle. It is conceivable to extend longitudinal vortex flow in composite flow networks through interacting with flip-flop flow exiting from a pre-fixed multiple-intersecting flow network in order to strengthen and thus stretch its efflux.

In this paper, the effect of several models representing the state of the art in wall-pressure fluctuations statistics were applied to the geometry of square rod bundles with P/D = 1.33, and used together with the random vibration theory to yield the spectral characteristics of rod vibration. Comparison of model predictions with experimental data representing rod acceleration allowed the selection of Efimtsov model as better suited for the rod bundles flow geometry and low frequency range. Further assimilating the mixing-vanes induced swirling flow as a disturbance to the parallel flow, two corrections were proposed based on comparison of measured vibration characteristics of vaned and vaneless bundles.

Some knowledge on damping and fluid-elastic instability is necessary to avoid flow-induced-vibration problems in shell and tube heat exchanger such as steam generator. Fluid-elastic instability is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. Experiments have been performed to investigate fluid-elastic instability of normal square tube bundles, subjected to two-phase cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and critical flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

An approximate analytical model for upward two-phase cross-flow through horizontal bundles, to predict drag coefficient on a cylinder and two-phase Euler number, has been developed. To verify the model, two sets of experiments were performed for various pitch mass fluxes of air-water mixture with void fraction. The experiments were undertaken with rotated triangular array of cylinders. The pitch to diameter ratio is 1.5 and the cylinder diameter 38 mm. The void fraction model proposed by Feenstra et al. (2000) is utilized to estimate the void fraction for the cross-flow in the tube bundle. An important variable on the drag coefficient is the two-phase friction multiplier. An empirical formulation of non dimensional pressure drop (Euler number) for single phase flow in tube bundles was proposed by Zukauskas et al. (1988) and two-phase friction multiplier in duct flow was formulated by various researchers. Considering the formulations, the present model was developed. It is found that Marchaterre’s model (1961) for two-phase friction multiplier is applicable to air-water mixtures. The analytical results agree well with experimental drag coefficients and Euler numbers in air-water mixtures for a sufficiently wide range of pitch mass fluxes and qualities. This model will allow researcher to provide analytical estimates of the drag coefficient, which is related to two-phase damping.

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures over a broad range of void fraction and mass fluxes. Both the dynamic lift and drag forces were measured with strain gage instrumented cylinders. The experiments revealed somewhat unexpected but significant quasi-periodic forces in both the drag and lift directions. The periodic forces appeared well correlated along the cylinder with the drag force somewhat better correlated than the lift forces. The periodic forces are also dependent on the position of the cylinder within the bundle.

The heat transfer tubes in steam generator of High Temperature Reactor-Pebble bed Modules (HTR-PM) suffer a high-speed and high temperature Helium flow environment. To avoid high thermal stress and decrease the fluid-induced vibration, tubes are packed in the form of rectangular tubes bundles. The empirical formulas of flow-induced vibration in ASME code are applicable to circular cylinder and incompressible media, which is not available for the proposed problem. In the present paper, rectangular tubes bundles are simplified as square cylinder with specific stiffness. The vibration of six square cylinders with horizontal and vertical arrangements are analyzed in displacement and frequency. The results show that the six square cylinders reveal same vibration amplitude and frequency, but different balance positions. For the horizontal arrangement and the vertical arrangement, according to the different balance positions, the balance position boundary line can be drawn. The cylinders at two sides of the balance position boundary line are closer to each other, where collisions or damages are easy to occur.

Natural convection heat transfer from vertical 7×7 rod bundle in liquid sodium was numerically analyzed to optimize the thermal-hydraulic design for the bundle geometry with equilateral square array, ESA. The unsteady laminar three dimensional basic equations for natural convection heat transfer caused by a step heat flux were numerically solved until the solution reaches a steady-state. The PHOENICS code was used for the calculation considering the temperature dependence of thermo-physical properties concerned. The 7×7 test rods for diameter (D = 7.6 mm), heated length (L = 200 mm) and L/d (= 26.32) were used in this work. The surface heat fluxes for each cylinder were equally given for a modified Rayleigh number, (Rf,L)ij and (Rf,L)Nx×Ny,S/D, ranging from 3.08×104 to 4.28×107 (q = 1×104∼7×106 W/m2) in liquid temperature (TL = 673.15 K). The values of S/D, which are ratios of the diameter of flow channel for bundle geometry to the rod diameter, for vertical 7×7 rod bundle were ranged from 1.8 to 6 on the bundle geometry with equilateral square array. The spatial distribution of average Nusselt numbers for a vertical single cylinder of a rod bundle, (Nuav)ij, and average Nusselt numbers for a vertical rod bundle, (Nuav,B)Nx×Ny,S/D, were clarified. The average value of Nusselt number, (Nuav)ij and (Nuav,B)Nx×Ny,S/D, for the bundle geometry with various values of S/D were calculated to examine the effect of array size, bundle geometry, S/D, (Rf,L)ij and (Rf,L)Nx×Ny,S/D on heat transfer. The bundle geometry for the higher (Nuav,B)Nx×Ny,S/D value under the condition of S/D = constant was examined. The general correlations for natural convection heat transfer from a vertical Nx×Ny rod bundle with the equilateral square and triangle arrays including the effects of array size, (Rf,L)Nx×Ny,S/D and S/D were derived. The correlations for vertical Nx×Ny rod bundles can describe the theoretical values of (Nuav,B)Nx×Ny,S/D for each bundle geometry in the wide analytical range of S/D (= 1.8 to 6) and the modified Rayleigh number ((Rf,L)Nx×Ny,S/D = 3.08×104 to 4.28×107) within −9.49 to 10.6 % differences.

In this paper, the flow-excited acoustic resonance of an in-line row of cylinders ranging from one to five is investigated. Cylinders of three different diameters of 12.7 mm, 19.1 mm, and 25.4 mm are tested in cross flow with flow speeds up to 160 m/s. Two different tube lengths of 76.2 mm and 127 mm are used to investigate the effect of the cylinder’s aspect ratio at a given diameter on the excitation mechanism of acoustic resonance. A fixed spacing ratio of L/D = 2 is used for all cases. For more than one cylinder of the larger diameter, the self-excitation of resonance occurs at two discrete flow velocity regions that are generally wider than the case of a single cylinder. A larger diameter does not only trigger the excitation of the pre-coincidence resonance region, but also increases the normalized acoustic pressure of this pre-coincidence resonance. On the contrary, the cylinder’s aspect ratio does not have a similar effect on the pre-coincidence and coincidence resonance regions. Therefore, it is important that the effect of diameter should be included in formulas predicting the occurrence of resonance for in-line tube bundles. In addition, the Strouhal number related to the coincidence resonance decreases with the increase in the number of cylinders. The coincidence resonance is related to the vortex shedding in the wake of the last cylinder, while the pre-coincidence resonance is related to the shear layer in the gap between successive cylinders.

It is common practice to accompany offshore pipelines by smaller diameter service lines or umbilicals to create a bundle. This gives rise to the so-called piggyback configuration. The flow behavior around the bundle is not well-known, leading to concerns on the stability of the configuration. This paper investigates the influence of the piggyback on the hydrodynamic loadings on the bundle in wave plus current condition using Computational Fluid Dynamics (CFD). Key parameters of the configuration that were investigated were the orientation of the smaller pipe with respect to the main pipeline and the flow conditions (different Keulegan-Carpenter numbers). The gap between the seabed and the main pipe was set to zero for all cases investigated. It was found that the hydrodynamic characteristics of the main pipe were significantly influenced by the presence of the piggyback. The numerical results also showed that the orientation of the piggyback plays an essential role in determining the drag, lift and inertia coefficients for the bundle. This phenomenon is explained by examining the vortex flow patterns around the cylinders. It is shown that the established industry practice of assuming the hydrodynamic characteristics of the bundle to be the same as an equivalent diameter cylinder may underestimate the forces on the bundle, and lead to a non-conservative design.

Flexible cylinders surrounded by a fluid flow that is dominantly aligned with the axis of the cylinders can be found in several applications. Examples with a flow confined to a narrow region around the cylinder(s) can be found in tube bundles of heat exchangers and reactor cores and also in air-jet weaving machines. This research analyses the flow-induced vibration of these two different cases with flexible cylinders in confined axial flow using numerical fluid-structure interaction (FSI) simulations. The FSI simulations of both cases use a partitioned framework, meaning that a computational fluid dynamics (CFD) solver is coupled with a finite element analysis (FEA) structural solver. The dynamic and kinematic equilibrium conditions at the contact surface between the fluid and the structure are satisfied by performing coupling iterations between both solvers in each time step. Convergence of these iterations is accelerated using quasi-Newton coupling techniques. For the case of the tube bundle, the modal characteristics have been identified for a tube bundle when they are submerged in an axial fluid flow. Furthermore, different types of flow-induced vibration have been studied. The flow speed has been increased in an FSI simulation of a single cylinder surrounded by an annular fluid domain, resulting first in static buckling and then in flutter at higher flow speeds. For the case of the air-jet weaving machines, the cylinder represents a smooth yarn which is accelerated by an air jet in the main nozzle of the machine, consisting of a long tube with small diameter. FSI simulations of a yarn clamped at the upstream end have been performed using the arbitrary Lagrangian-Eulerian formulation with deforming grids in the fluid domain. This work demonstrates the feasibility of analyzing and predicting flow-induced vibration of cylinders in confined axial flow by performing FSI simulations. The results of simulations are compared with those of experiments for tubes in axial flow and for a yarn in a nozzle of an air-jet weaving machine.