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Sumner, David. "Circular cylinders in cross-flow." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0027/NQ50265.pdf.
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Sumner, David 1969. "Circular cylinders in cross-flow." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35947.
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Small groups of circular cylinders of equal diameter, in tandem, side-by-side and staggered configurations, were investigated in steady mean cross-flow, and under conditions of an impulsive start, for Reynolds numbers from 500 to 6000. Experiments were conducted in water in three facilities, using flow visualization, hot-film anemometry and particle image velocimetry (PIV). The emphasis was on acquiring an improved physical understanding of the fluid behaviour, and the dynamics of the vortical structures in the flow, as the number of cylinders, the spacing between the cylinders, and the angle of incidence with respect to the oncoming flow, were varied.<br>For tandem cylinders in impulsively started flow, the development showed constrained streamwise growth and lateral expansion of the gap recirculation zones at small and intermediate pitch ratios. Under steady cross-flow conditions, reattachment of the free shear layers from the upstream cylinder, onto the surface of the downstream cylinder, was found to occur in an alternating, non-continuous, and non-simultaneous fashion, in a process synchronized with Karman vortex shedding from the downstream cylinder. Within the gap between the cylinders, bounded on either side by the reattaching shear layers, was found weakly rotating or stagnant fluid, with vorticity concentrations only near the points of reattachment.<br>The temporal development of the side-by-side configuration was dominated by strong flow through the gaps between the cylinders, rapid breakup of the recirculation zones behind the outer cylinders, gap vortex shedding, and the formation of a counter-rotating vortex pair in the combined wake. Under steady mean cross-flow conditions, the PIV vorticity data showed instantaneous variation in the base-bleed flows, the gap flow deflection angles and the vortex formation lengths. In the three-cylinder side-by-side configuration, vortex shedding frequency measurements were sensitive to the measurement location.<br>For the two-cylinder staggered configuration in steady cross-flow, nine flow patterns were identified, and processes of vortex pairing, enveloping, impingement and induced separation were observed. Some new insight was gained into previously published force coefficient and Strouhal number data, by considering the flow patterns responsible. The study revealed that vortex shedding frequencies are more properly associated with the individual shear layers, rather than with the individual cylinders.
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Hayder, Mir Mohammad Abu 1976. "Cross-flow past oscillating circular cylinders." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115685.
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The cross-flow past a pair of equal-diameter circular cylinders, arranged in a staggered configuration, was investigated experimentally in a closed-circuit water tunnel at Reynolds numbers, based on the mean-flow velocity and the cylinder diameter, within the lower subcritical range. The wake formation process was studied employing dye-injection flow visualization and hot-film measurements. The main emphasis was placed on acquiring a physical understanding of the mechanisms leading to vortex shedding, and particularly on the effect of a forced oscillation transverse to the flow direction of either of the two cylinders. For comparison purposes, investigations were also carried out with both cylinders stationary.<br>Experimental results showed that, for a reasonably large angle of incidence, the flow in the wake of a stationary cylinder pair could be characterized by two distinct periodicities, each of which was dominant on one side of the wake. Furthermore, for lower Reynolds numbers (Re < 1.0x10 4), there was an integral relationship between the two Strouhal numbers, but this integral relationship was no longer maintained for Re > 1.0x10 4. On the other hand, the flow around stationary cylinders for a small angle of incidence was characterized by a single Strouhal number, which remained approximately constant over the entire Reynolds number range.<br>For all the cylinder configurations investigated the wake flow patterns remained essentially the same as those of the corresponding static cases, when either of the two cylinders was forced to oscillate with a nondimensional forcing frequency less than approximately 0.10. However, beyond this value, the wake underwent considerable modification vis-a-vis when the cylinders were stationary, and the flow pattern within the wake was strongly dependent on the value of the forcing frequency. In particular, there were distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation; these synchronization regions involved sub- and superharmonics as well as fundamental synchronizations. With either upstream or downstream cylinder oscillation, the wake on the mean-flow side of the downstream cylinder synchronized with the shear layers separated from its outer surface, whereas synchronizations on the mean-flow side of the upstream cylinder were caused by the periodicities formed from the interaction of the other three shear layers.<br>The flow phenomena associated with the synchronizations were described in detail via flow visualization. The organization of the wake was strongly dependent on whether it was the upstream or downstream cylinder which was oscillating. The synchronized wake on the mean-flow side of the downstream cylinder at both lower and higher oscillation frequencies for upstream cylinder oscillation was observed to form either by the shedding of independent vortices or by the coalescence of two or more vortices. However, for downstream cylinder oscillation, although the synchronizations on this side of the wake at lower oscillation frequencies were caused by the shedding of independent vortices or by the coalescence of vortices, those at higher oscillation frequencies were the consequence of the coalescence of vortices only. For large incidence angles, the number of shear layers separated from the downstream cylinder which interacted with those separated from the upstream cylinder was critical in causing the synchronizations on the mean-flow side of the upstream cylinder.<br>In most cases, the flow for all the cylinder configurations traversed between the same patterns as those obtained when the cylinders were placed stationary at their minimum and maximum transverse spacings; but there were also some situations where the oscillation of either cylinder pushed the flow outside the regimes associated with the stationary configurations. The synchronization ranges obtained when the upstream or downstream cylinder was oscillating were different from each other, and these ranges were much wider than the corresponding synchronization ranges for a single oscillating cylinder. For two cylinders, an analysis of the fundamental synchronization showed that the frequency range over which this occurred was much broader for upstream cylinder oscillation than for downstream cylinder oscillation. Also, the fundamental synchronization ranges for downstream cylinder oscillation were closer to those for single cylinder oscillation in comparison to those for upstream cylinder oscillation.
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Gordon, David R. "Computational unsteady flow dynamics : oscillating flow about a circular cylinder." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28053.
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Levold, Pål. "Viscous Flow Around Finite Lenght Circular Cylinder." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18641.
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Viscous flow around circular cylinders is a classical research topic in fluid dynamics with a vast amount of practical applications in the field of offshore marine technology. In the flow around cylinders of finite length, complex wake behaviours and coherent structures occur even at relatively low Reynolds numbers. An understanding of the nature and dynamics behind such behaviour could form a basis for improved designs and innovative solutions for offshore and subsea constructions.In the present study, flow around long finite cylinders at Re = 100 is investigated numerically using the incompressible Navier-Stokes Equations solver MGLET. To study the isolated flow near the free end, a cylinder with aspect ratio L/D = 50 is chosen. The flow over the free end gives rise to a wake consisting of two vortex shedding cells with different shedding frequencies; one small near the free end and one larger in the central region of the span. It is found that each vortex shed in the end cell bends horizontally and connects with the upstream vortex shed from the opposite side of the cylinder. The horizontal vortex shedding is found to give rise to a pair of trailing vortices in the time averaged flow.When a vortex is shed with a large phase difference between the two cells, the vortex is split and connects with other surrounding vortices. This phenomena is commonly referred to as vortex dislocations and occurs with the beat frequency, i.e. the difference between the two vortex shedding frequencies. It is found that this frequency can be detected in time histories of $u$ in the wake at the spanwise centre.A second configuration, consisting of a wall mounted cylinder with aspect ratio L/D = 25 is simulated in order to study the effect of introducing a no-slip surface. The effect on the end cell is found to be minimal, while the central cell shedding frequency is reduced. Comparisons with published data on a cylinder with aspect ratio L/D = 25 and two free ends shows that both the reduction of aspect ratio and the introduction of the no-slip boundary condition contributes to the reduced shedding frequency.
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Matko, T. I. R. "Two-phase flow in circular secondary sedimentation tanks." Thesis, Cranfield University, 1997. http://dspace.lib.cranfield.ac.uk/handle/1826/3920.
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The main objective of this work was to optimise a numerical model to predict the flow in circular secondary sedimentation tanks. The numerical models in the literature were reviewed and the new opportunities for research were identified. Single-phase flow characteristics of two circular sedimentation tanks were investigated using the CFD program, CFX-F3D. The flow in the circular clarifiers were modelled in two dimensions (axial and radial) and using the standard k-E turbulence model. Results indicated that a vertical inlet instead of a horizontal inlet did not improve the correlation with the experimental data in a pilot-scale tank. Modelling the diurnal variation in flow to a full-scale tank significantly improved the correlation with experimental data. The 'Eulerian multi-fluid' model in the program, CFX-F3D was modified to predict the flow in circular secondary sedimentation tanks. The model compared quite closely with the measured residence time of the effluent and return activated sludge (RAS) in a conventional secondary clarifier. The residence time of the effluent in another secondary clarifier with a turbulent jet, was over-predicted. The mean particle diameter in the model was found by comparing the numerical predictions with experimental data. The particle diameter was between 100 to 190 μm for the secondary clarifiers, which was in agreement with the experimental data in the literature. The flow patterns in the conventional secondary clarifier were affected by the particle density, particle diameter, axial slip velocity, colloids settling parameter, axial turbulent Prandtl number, inlet flow rate and inlet solids concentration. A 3-D simulation of the conventional secondary clarifier was in agreement with a 2-D simulation. Recommended values were given for all these parameters. However, the drag force between the phases was not formulated correctly and the water surface was modelled as a symmetry plane. Therefore, some more work is still required to make suitable modifications to the model.
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Fung, Ka Shuen. "Separated and reattaching flow on a circular cylinder." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339118.
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盧建弘 and Kin-wang Lo. "The flow dynamics of an asymmetric circular cylinder." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31235116.
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AlRefaie, Abdulaziz M. "Flow Control Around Circular Cylinder: Ventilation holes Method." University of Toledo / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1260201547.
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Lo, Kin-wang. "The flow dynamics of an asymmetric circular cylinder /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B17490741.
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AlRefaie, Abdulaziz Mohammed. "Flow control around circular cylinder : ventilation holes method /." Connect to full text in OhioLINK ETD Center, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1260201547.
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Thesis (M.S.)--University of Toledo, 2009.<br>Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science Degree in Mechanical Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 51-54.
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Selvam, Kamal. "Transition to turbulence in circular expansion pipe flow." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMLH32/document.
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La thèse traite de recherches numériques et expérimentales sur l’écoulement à traves des conduites circulaires ou des tubes avec une petite entrée et un diamètre de sortie plus grand, parfois appelées élargissement ou divergents. L’écoulement dans un élargissement est globalement stable pour des nombres de Reynolds élevés. Ainsi la simulation numérique de ce type d’écoulement nécessite de grands domaines de calcul contenant la zone de recirculation, qui croît linéairement. En outre, les études expérimentales dans les élargissements brusques indiquent que la transition se produit à des nombres de Reynolds plus faibles que prévue par la théorie linéaire de stabilité. La raison pour cette transition précoce est due à la présence d’imperfections dans le dispositif expérimental, qui agit comme une perturbation d’amplitude finie de l’écoulement. Des simulations numériques directes des équations de Navier-Stokes ont été réalisées avec deux types différents de perturbations (i) l’inclination et (ii) le vortex. Tout d’abord, la perturbation de type inclinaison, qui est appliqué à l’entrée, crée une zone de recirculation asymétrique, puis se casse pour former une turbulence localisée en aval de l’expansion. Deuxièmement, la perturbation de type vortex, crée des structures qui ressemblent à un mode azimutal d’ordre inférieur, déjà identifié comme une perturbation optimale amplifiée. Il croît en raison de l’instabilité convective, puis forme une tâche de turbulence localisée. Enfin, la corrélation spatiale et la décomposition en modes propres révèlent que cette turbulence localisée obtient son énergie de l’écoulement d’entrée<br>The thesis deals with numerical and experimental investigations of flow through circular pipes with smaller inlet and larger outlet diameter, also known as expansion pipes. The hydrodynamic expansion pipe flow is globally stable for high Reynolds number. In order to numerically simulate these types of flows, large computational domains that could accommodate the linearly growing symmetric recirculation region is needed. Moreover, experimental studies of expansion pipe flows indicate that the transition occurs at lower Reynolds number than predicted by the linear stability theory. The reason for early transition is due to the presence of imperfections in the experimental setup, which acts as a finite-amplitude perturbation of the flow. Three-dimensional direct numerical simulations of the Navier-Stokes equations with two different types of perturbations (i) the tilt and (ii) the vortex are investigated. First, the tilt perturbation, which applied at the inlet, creates an asymmetric recirculation region and then breaks to form localised turbulence downstream the expansion section. Second, the vortex perturbation, creates structures that looks like lower order azimuthal mode, resembles an optimally amplified perturbation. It grows due to convective instability mechanism and then breaks to form localised turbulence. Spatial correlation and the proper orthogonal decomposition reveal that this localised turbulence gains it energy from the core flow coming out of the inlet pipe
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Hanson, Craig D. "Numerical Analysis of Oscillating Flow about a Circular Cylinder." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305867.
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Bjørkli, Rune. "Numerical Simulations of Viscous Flow Around Stepped Circular Cylinder." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18612.
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A stepped cylinder could be a desired design for an offshore buoy or SPAR platform. The geometry of a stepped cylinder consists of a small diameter cylinder (d) placed on top of a large diameter cylinder (D). This master thesis has investigated numerically the flow around a stepped cylinder with different diameter ratios (d/D) for a Reynolds number, ReD = 150. The commercial software Fluent v13.0 by Ansys was used for the numerical investigation.The aim of the study has been exploring the nearby wake flow as well as the region where the two cylinders are joined. The hydrodynamic forces and vortex shedding frequency have been analysed and compared for the four different diameter ratios: d/D = 0.3, 0.5, 0.8 and 0.9The major part of the published papers on the topic is based on experimental studies. Only two papers are based on numerical studies, having considered d/D = 0.5 exclusively. Earlier studies have focused mainly on vortex shedding in the wake flow, omitting the forces acting on the stepped cylinder.The stepped cylinder has been modelled using the software GAMBIT. A convergence study investigating the domain size and element density was conducted to ensure a grid independent solution. Special attention was directed at the step region to fully resolve the complex flow in this region. The numerical model was verified to be in good agreement with previous experimental- and numerical studies.For the stepped cylinders significant spanwise velocity was detected in the step region. For d/D = 0.3 and 0.5, upflow was detected over the leading edge of the step whereas downwash characterised the trailing edge of the step. Similarities to the flow around a finite length cylinder could be drawn for d/D = 0.3 and 0.5, whereas d/D = 0.8 and 0.9 resembled that of a straight cylinder.The step was found to affect the wake flow &#8776; 10D into D independent of diameter ratio. The wake flow behind the small diameter cylinder was less affected by the step than the large for d/D < 0.5. In the step region two distinct streamwise vortices were detected. A pair of edge vortices as well as a junction vortex were readily detected for d/D = 0.3 and 0.5. The junction vortex was not detected for d/D = 0.8 and 0.9 due to the small step change in diameter.The drag force on D was found to increase as d/D increased. Similarly, the amplitude of the lift force was also found to increase as d/D increased. The mean drag-coefficient varied along the span with peaks in the local drag-coefficient observed in close vicinity of the step.Regular spanwise vortex shedding was detected away from the step at a frequency similar to that of a straight cylinder. In the step region, located mainly on D, a cell of lower vortex shedding frequency was detected for d/D = 0.3 and 0.5. As d/D increased this cell seemed to disappear. Suppression of regular vortex shedding close to the step for d/D = 0.3 was observed for ReD = 150, 300 and 600. For ReD > 150 the large spanwise vortex structures were still discernible, but the presence of small-scale streamwise vortices complicated the flow.
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Zhao, Xingyuan. "Cross-flow around and stability of multiple circular cylinders." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=13231.
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Lotshaw, John E. "Numerical analysis of oscillating flow about a circular cylinder." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23993.
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Tabrizi, Seyed Pariviz Alavi. "Jet impingement onto a circular cylinder." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263841.
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Tasar, Gursu. "Experimental Investigation Of Near And Far Field Flow Characteristics Of Circular And Non-circular Turbulent Jets." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610256/index.pdf.
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The atomization problem of high speed viscous jets has many applications in industrial processes and machines. In all these applications, it is required that the droplets have high surface area/volume ratio meaning that the droplets should be as small as possible. This can be achieved with high rates of turbulence and mixing of the flow. In order to constitute a foresight of geometry eects on droplet size, experimental investigation and the determination of flow characteristics in near and far fields of a low-speed air jet have been performed. In order to fulfill this task, three components of instantaneous velocity are measured, using a triple sensor Constant Temperature Anemometer (CTA) system. Through these measurements, mean velocity, Reynolds stress, velocity decay, spreading rate, turbulent kinetic energy, vorticity, and mass entrainment rate values are obtained. Stress-Strain relationship is also observed. Measurements are obtained for a baseline circular nozzle (round jet) as well as for an equilateral triangular and a square nozzle. On the basis of these measurements, the equilateral triangular jet is found to be the best option in order to get highest turbulence and mixing level with smallest core length.
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Collins, Patrick M. "Point Doppler velocimetry measurements in circular jets." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1304.
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Thesis (M.S.)--West Virginia University, 2000.<br>Title from document title page. Document formatted into pages; contains vii, 120 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 40-42).
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Mendes, João Batista. "Soleira elíptica-circular." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3147/tde-19082008-171341/.
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Este trabalho propõe uma soleira assimétrica elíptica-circular com apenas dois pontos de descontinuidade, com parâmetros geométrico associados à vazão específica de projeto, com possibilidade de padronização e cujas características hidráulicas (linha d´água, pressões, coeficiente de vazão) podem ser determinadas teoricamente. Um sistema de equações diferenciais parciais permite o desenvolvimento de um modelo computacional para determinação dos valores teóricos dessas características. A validação dos valores teóricos das características hidráulicas da soleira por um modelo computacional foi realizada com a confrontação desses mesmos valores obtidos em um modelo físico, permitindo a comparação de pressões, linha d´água, coeficiente de vazão e profundidade crítica.<br>In this work is proposed an asymmetrical (elliptical-circular) weir with two points of discontinuity only, with geometrical parameters associated to the specific design discharge, allowing the standardization, and whose hydraulic characteristics (water profile, pressures and discharge coefficient) may be theoretically determinate. Their hydraulic characteristics, developed by a system of partial differential equations, system allowing the development of a computational model to determine the theoretical values of the weir hydraulic characteristics. The validation of these theoretical values of the weir hydraulic characteristics, obtained by a computational model, was made by the comparison between the values of water profile, pressures, discharge coefficient and critical depth obtained by the theoretical model and the values obtained by the physical model.
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Miranda, Sergio. "Active Control of Separated Flow over a Circular-Arc Airfoil." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/34411.
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An experimental study of active control of fully separated flow over a symmetrical circular-arc airfoil at high angles of attack was performed. The experiments were carried out in a low-speed, open circuit wind tunnel. Angles of attack from 10 to 40 degrees were tested. Low-power input, unsteady excitation was applied to the leading or trailing edge shear layers. The actuation was provided by the periodic oscillation of a 4-percent-chord flap placed on the suction side of the airfoil and facing the sharp edge. Vortex-shedding frequencies were measured and harmonic combinations selected as the applied actuator frequencies.
Pressure measurements over the airfoil show that the control increased the normal force coefficient by up to 70%. This supports the idea of vortex capture in the time-averaged sense, enhancing the lift on the airfoil by managing the shear layer roll up.
The results indicate the viability of the control of large-scale flow fields by exploiting the natural amplification of disturbances triggered by small-scale actuators.
The application of flow control on sharp-edged aircraft wings could lead to improved maneuverability, innovative flight control and weight reduction. These can be achieved by inexpensive, low-power, rugged actuators.<br>Master of Science
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Engelbreth, Knut Inge. "Viscous flow around a circular cylinder near a plane wall." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15482.
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Marine pipelines placed at or near the seabed are exposed to currents and waves. In the presence of a sedimentary seabed, the interaction between the surrounding water motions and the pipeline may cause erosion of sediments beneath the pipeline. Due to this erosion or due to the installation procedure, free spans may occur in sections along the span of the pipeline. A simplified description of the flow is obtained by approximating the seabed as a plane and impermeable wall. Most of the previous experimental and numerical studies on this flow are performed at Reynolds numbers, Re, in the range 103-105 as this range is of most relevance for offshore engineering purposes. Numerical modeling at such Reynolds numbers generally involves different kinds of artificial flow modeling. In this study, the software OpenFOAM is applied for numerical simulations of the viscous flow around a circular cylinder at Re= 100. At this Reynolds number the flow around an unconfined circular cylinder is characterized by vortex shedding and yet turbulence is avoided, which provides the possibility of accurate calculations of the flow. The flow is investigated with reference to visualizations of pressure, velocity and vorticity; and the flow characteristics are quantified in terms of drag and lift acting on the cylinder and vortex shedding frequency. Numerical simulations of an unconfined cylinder in uniform cross-flow constitutes the basis of the present study, and these simulations are included in an attempt to validate the results and the applied computational method. The results for this flow are within the scatter of the reported values in the literature. In this study, the flow around a cylinder near a plane wall is of main interest. Three different gap ratios G/D=0:2;0:5;1:0 are applied. The results are generally in accordance with published data from numerical simulations; best agreement is found at G/D=0:2 and G/D= 0:5. The results are supportive to the suggestion of vortex shedding suppression to be caused by the interaction between the lee-side recirculating flow and the gap flow, which inhibits large-scale vortex roll-up. Further, the results at G/D= 1:0 indicates cancellation of opposite signed vorticity in the near-wall region, in accordance with suggestions in the literature. Additionally, the geometry of the wall is altered, introducing a hollow below the cylinder. This shape imitates a fully developed scour profile. These simulations are expected to bring new results to this topic of research. The flow is characterized by evident vortex shedding. Further, at this gap a distinct mean lift in the direction towards the wall is observed and both the drag coefficient and the frequency of vortex shedding is reduced as compared to the flow around a cylinder in uniform cross-flow. The obtained results exhibits similarity to published experimental data for the flow at Re= 1:104. Two-dimensional simulations are performed for all of the flow configurations, and a few three-dimensional simulations are performed for a cylinder in uniform cross-flow and a cylinder located a distance G/D= 0:5 from a plane wall. Due to the two-dimensional flow patterns, insignificant differences are found between the two-dimensional and three- dimensional simulations. In this study, emphasize is given to the influences on the solution of the following numerical parameters: time step, domain size, grid geometry, element size and element spacing. These parameters are thoroughly investigated in terms of convergence studies. Also included in this thesis is a review of some features of these flows and an overview of the governing equations, OpenFOAM and the applied solver icoFoam.
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Seto, Mae L. "Flow interference effects between two circular cylinders of different diameters." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29762.
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This thesis investigates different examples of action at a distance, namely the interaction
of two circular cylinders of different diameters and the interaction of a cylinder with a wall in various arrangements. Action at a distance modifies both the lift and drag of each one of the objects. The fluid flow interaction between a circular cylinder (of diameter D) with a wall, and a circular cylinder with a smaller (¼D) circular cylinder at Reynolds numbers of ≈ 10,000 were of interest. Manifestations
of the interactions include mutual changes in the lift and drag forces, phase, onset and frequency of vortex shedding on the circular cylinders/wall. A novel force measurement device for lift and drag of circular cylinders and a data acqusition system was built to realize the above experiments in a water towing tank. The system was capable of simultaneously measuring lift and drag on two circular cylinders with time resolution and correlating these measurements with flow field pictures. Measurements of the lift and drag and phase, onset and frequency of vortex shedding were taken on the large and small cylinder simultaneously as a function of the relative position between itself and the smaller cylinder as the two are towed. These measurements make it possible to map out the areas within the cylinders' sphere of influence and measure the intensity of this influence as a function
of the distance between the two cylinders. Every quantity that was mutually altered by the presence of another cylinder is used as measurements of the area of influence for a circular cylinder. It was found in general that the forces act up to a distance of about 3 diameters in the lateral direction. It was also noted that pressure fluctuations at the vortex shedding frequency penetrate into the laminar flow region up to about 3D in the lateral direction. The results agree with existing
results for wall/cylinder proximity experiments and flow interference between identical
circular cylinders. A novel method to trigger the onset of vortex shedding for towing tanks was also discovered.<br>Science, Faculty of<br>Physics and Astronomy, Department of<br>Graduate
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Tewnion, Angus Jamieson. "Steady and unsteady flow simulations in a circular closed conduit." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20810.pdf.
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Johnson, A. R. "Flow resistance in circular tubes rotating about a parallel axis." Thesis, University of Hull, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233988.
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Li, Meng. "Flow and heat transfer characteristics of impinging circular synthetic jets." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494598.
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Since the introduction of integrated circuits forty years ago, the cooling of electronic components has become increasingly critical as the result of the exponential growth in transistors density on the integrated circuits. It becomes apparent that a more compact yet more efficient cooling method must be developed in order to satisfy the pressing need of future electronics. Synthetic jets offer an attractive cooling method due to their massless nature and relative ease in being integrated in MEMS through micro-fabrication. Although the research on synthetic jets cooling has shown a promising prospect in the applications of cooling electronic components, our current knowledge of the behaviour of impinging synthetic jets is still insufficient for designing such devices which can deliver the required performance. In this research project, a series of experimental studies were undertaken so as to achieve a better understanding of the fluid mechanics and heat transfer characteristics of impinging synthetic jets issued from a circular and twin circular orifices. The finding from this study is expected to provide useful information to the design of effective synthetic jet cooling devices.
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Rullan, Jose M. "Flow Control Over a Circular Arc Airfoil by Periodic Blowing." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/10178.
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The flow over sharp-edged wings is almost always separated. The control of separated flows is possible and benefits can be achieved but only in a time average sense. A new design of an actuator was designed and tested which can achieve a wide range velocity of without frequency dependence, is free of oscillating components as well as free of secondary frequencies and therefore can be scaled up easily, unlike a traditional synthetic jet. The actuator can achieve a considerable amount of jet vectoring, thus aligning the disturbance with the leading edge shear layer.
Results indicate that unsteady mini-jet actuation is an effective actuation device capable of increasing the lift in the stall region of the airfoil. Moreover, pressure measurements showed that two parameters could be altered to maximize the lift. The momentum coefficient needed a minimum value to exert influence and the actuating frequency need not be at exact the natural shedding frequency to improve the lift and can be operated at harmonics of the natural shedding frequency and obtain improvements.<br>Master of Science
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Vishwanadula, Harikrishna. "Experimental investigations on the flow of nanofluids through circular pipes /." Available to subscribers only, 2008. http://proquest.umi.com/pqdweb?did=1594486971&sid=3&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Brown, Jason Britton. "An experimental facility for the investigation of the flow in a circular-couette flow bioreactor." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/18174.
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De, Vecchi Adelaide. "Wake dynamics of flow past a curved circular cross-section body under cross-flow vibration." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502910.
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Canabes, Jose Patricio Gallardo. "Direct Numerical Simulation of the Flow Past a Curved Circular Cylinder." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11466.
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Offshore marine applications often include configurations of cylindrical structures that produce complex three-dimensional flow features. Catenary risers, for instance, can create complex flow patterns when subjected to hydrodynamic loads. In recent published studies, the shape of a catenary riser has been approximated by a quarter segment of a ring followed by a horizontal extension, obtaining a curved circular cylinder. In the present Master thesis, Direct Numerical Simulations at Re = 100 and 500 have been conducted in order to study the flow past such geometry. The main flow direction was parallel to the plane of curvature of the cylinder and directed towards the convex face of the quarter-of-ring. Additionally, a sheared incoming flow has been considered in the analysis by imposing a linearly varying velocity profile at the inlet. The shedding mechanism observed in uniform flow was similar to that reported in previous published studies. One single shedding frequency prevailed along the entire span of the cylinder at Re = 100 and 500. Moreover, the vortex cores at Re = 100 were normal to the flow direction and exhibited slight distortions as they were convected downstream, whereas at Re = 500 the wake topology was characterized by three-dimensional structures of smaller scale. A sheared inflow, on the other hand, gave rise to an oblique and cellular vortex shedding pattern with two cells of different shedding frequencies. The strong slanting of the vortices, as well as the cellular pattern, was clearly induced by the variation of the local Reynolds number along the front stagnation point. The basic knowledge gained from this thesis appear as very promising in the context of marine structures, it is therefore expected that this work will constitute a basis for further investigations considering this type of geometry.
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Thingbø, Sunniva Selstad. "Simulation of viscous Flow around a circular Cylinder with STAR-CCM+." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22378.
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In this thesis, three-dimensional modelling of the flow around a circular cylinder isaccomplished. Two cases are considered. The first (Case 1) is a cylinder in steady,uniform current subjected to Reynolds number 3900. The second case (Case 2) isa cylinder in the vicinity of a rigid wall, also at Reynolds number 3900. For thesecond case, both a boundary layer velocity profile (Case 2a) and a uniform inletvelocity profile (Case 2b) is simulated. The gap-to-diameter ratio, e/D, is set to 0.2 for Case 2. Large eddy simulations (LES) with Smagorinsky subgrid scale (SGS)model are applied to simulate the flow. LES have ability to resolve fine structuresin the turbulent wake of the cylinder. A mesh convergence study is accomplishedfor Case 2a.In the first part of the thesis, the background theory for the case is given in addition to information about the applied pre- and postprocessing tools. In the lastpart of the thesis, the case set-up is described and the results are presented anddiscussed. Velocity profiles in the cylinder wake, hydrodynamic values and pressuredistribution on the cylinder wall are investigated to give a better understandingof the physics in the cases. The results are compared to published experimentalmeasurements and numerical studies.For the first case, the results tend to agree well with published research. The softwaresystem with LES and the Smagorinsky subgrid scale model does successfullysimulate the flow in the boundary layers, the shear layers and the near wake. Theresults are interesting in the context of flow bifurcation for at cylinder subjectedto Reynolds number 3900.The vortex shedding is suppressed for both Case 2a and Case 2b, as expected. Forthe cylinder in Case 2a, a decreased drag coefficient is observed when comparedto Case 1. This is not observed for the cylinder in Case 2b. The two cases areobserved to have an increased mean lift coefficient caused by the vicinity of the wall. However, for Case 2b, the increase is of larger magnitude. This is addressed to the pressure distribution on the cylinder surface. There are also observed differences in the wake statistics for Case 2a and Case 2b. It is concluded that both gap-todiameter ratio and boundary layer thickness have a significant influence on the flow around a circular cylinder.
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Kirkconnell, Carl Scott. "Experiments on the stability characteristics of an unsteady circular couette flow." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16400.
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湯健東 and Kin-tung Dick Thung. "Digital PIV techniques for studies of circular cylinder under oscillating flow." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31223473.
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伍智榮 and Chi-wing Ng. "Interactions of vortices from two circular cylinders in bistable flow regime." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B3123608X.
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Christopoulos, George P. "Oscillating-flow wind tunnel studies for a circulation control circular cylinder." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28435.
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CUNHA, PHILEMON MELO. "THERMOHYDRAULIC CHARACTERISTICS OF TURBULENT FLOW IN SMOOTH AND PINNED CIRCULAR CONFIGURATIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1987. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19124@1.
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Coeficientes de queda de pressão e transferência de calor foram determinados experimentalmente para escoamento turbulento em dutos circulares e semi-circulares lisos e pinados. Pinos de seção transversal circular foram colocados na superfície interna dos dutos. As experiências foram realizadas utilizado-se vários tipos de trocadores de calor, eram ar e água. Para se atingir condições totalmente desenvolvidas, os trocadores de calor possuíam um cumprimento de entrada de 25 diâmetros . Os coeficientes médios de troca de calor foram determinados através da medida dos coeficientes globais de troca de calor dos trocadores de calor. Números de Nusselt e coeficientes de atrito são apresentados como funções do número de Reynolds do escoamento. A finalidade de tal comparação foi estudar a influência dos pinos de seção circular na queda de pressão e taxa de transferência de calor . Números de Nusselt e coeficientes de atrito são apresentados como funções do número de Reynolds do escoamento. Os resultados para dutos lisos e pinados foram comparados. A finalidade de tal comparação foi estudar a influência dos pinos da seção circular na queda de pressão e taxa de transferência de calor. O desempenho térmico global de superfícies pinadas depende principalmente do número de Nusselt e da eficiência da região. Assim, resultados para a eficiência do pino foram também apresentados.<br>Pressure drop and heat transfer coeficients have been experimentally determined for turbulent flow in smoth and pin finned circular and semi-circular ducts. Spines of circular cross section were attached to the internal surface of the ducts. The experiments were perfomermed by utilizing several types of heat exchanges. The flowing fluids, in the heat exchangers, were air and water. In order to attain fully developed conditions, the heat exchangers had a starting longth of 25 diameters. The average heat tranfer coefficients were determined by measuring the overall heat tranfer coefficients of the heat exchangers. Nusselt numbers and friction factors are presented as fuctions of the flow Reynolds number . The purpose of such comporison was to study the influence of the spines of circular cross section on the pressure drop and heat transfer rate. The overall thermal performance of pin finned surfaces depends mainly on the Nusselt number ando n the region efficiency. Then, results for the pin fin efficienty were also presented.
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Cardell, Gregory Scott Roshko A. "Flow past a circular cylinder with a permeable wake splitter plate /." Diss., Pasadena, Calif. : California Institute of Technology, 1993. http://resolver.caltech.edu/CaltechETD:etd-04012005-092116.
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Fredrickson, Kent Allen. "Numerical study of non-impulsively started flow around a circular cylinder." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238051.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1990.<br>Thesis Advisor(s): Sarpkaya, Turgut. "September 1990." Description based on title screen as viewed on December 16, 2009. DTIC Identifier(s): Channel flow, cylinders, wake, impulsive flow, theses. Author(s) subject terms: Hydrodynamics, numerical calculations, wake, cylinder, impulsive flow. Includes bibliographical references (p. 65-66). Also available in print.
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Ng, Chi-wing. "Interactions of vortices from two circular cylinders in bistable flow regime /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18037379.
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Thung, Kin-tung Dick. "Digital PIV techniques for studies of circular cylinder under oscillating flow /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22029783.
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Yang, Ching-Tai, and 楊慶泰. "Stability of modulated circular Couette flow." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/84141118326710335176.
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Pan, Zhi-Shi, and 潘志實. "Construction of Graphs with Given Circular Chrotmatic Number or Circular Flow number." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/01222847836257426912.
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博士<br>國立中山大學<br>應用數學系研究所<br>91<br>This thesis constructs special graphs with given circular
chromatic numbers or circular flow numbers.
Suppose $G=(V,E)$ is a graph and $rgeq 2$ is a real number. An
$r$-coloring of a graph $G$ is a mapping $f:V
ightarrow [0,r)$
such that for any adjacent vertices $x,y$ of $G$, $1leq
|f(x)-f(y)|leq r-1$. The circular chromatic number $chi_c(G)$
is the least $r$ for which there exists an $r$-coloring of $G$.
The circular chromatic number was introduced by Vince in 1988 in
cite{vince}, where the parameter is called the {em star
chromatic number} and denoted by $chi^*(G)$. Vince proved that
for any rational number $k/dgeq 2$ there is a graph $G$ with
$chi_c(G)=k/d$. In this thesis, we are interested in the
existence of special graphs with given circular chromatic numbers.
A graph $H$ is called a minor of a graph $G$ if $H$ can be
obtained from $G$ by deleting some vertices and edges, and
contracting some edges. A graph $G$ is called $H$-minor free if
$H$ is not a minor of G. The well-known Hadwiger''s conjecture
asserts that for any positive integer $n$, any $K_n$-minor free
graph $G$ is $(n-1)$-colorable. If this conjecture is true, then
for any $K_n$-minor free graph $G$, we have $chi_c(G)leq n-1$.
On the other hand, for any graph $G$ with at least one edge we
have $chi_c(G)geq 2$. A natural question is this: Is it true
that for any rational number $2leq rleq n-1$, there exist a
$K_n$-minor free graph $G$ with $chi_c(G)=r$?
For $n=4$, the answer is ``no". It was proved by Hell and Zhu in
cite{hz98} that if $G$ is a $K_4$-minor free graph then either
$chi_c(G)=3$ or $chi_c(G)leq 8/3$. So none of the rational
numbers in the interval $(8/3,3)$ is the circular chromatic number
of a $K_4$-minor free graph. For $ngeq 5$, Zhu cite{survey}
proved that for any rational number $rin[2,n-2]$, there exists a
$K_n$-minor free graph $G$ with $chi_c(G)=r$. The question
whether there exists a $K_n$-minor free graph $G$ with
$chi_c(G)=r$ for each rational number $rin(n-2,n-1)$ remained
open. In this thesis, we answer this question in the affirmative.
For each integer $ngeq 5$, for each rational number
$rin[n-2,n-1]$, we construct a $K_n$-minor free graph $G$ with
$chi_c(G)=r$. This implies that for each $ngeq 5$, for each
rational number $rin[2,n-1]$, there exists a $K_n$-minor free
graph $G$ with $chi_c(G)=r$. In case $n=5$, the $K_5$-minor free
graphs constructed in this thesis are actually planar graphs. So
our result implies that for each rational number $rin[2,4]$,
there exists a planar graph $G$ with $chi_c(G)=r$. This result
was first proved by Moser cite{moser} and Zhu cite{3-4}. To be
precise, Moser cite{moser} proved that for each rational number
$rin[2,3]$, there exist a planar graph $G$ with $chi_c(G)=r$,
and Zhu cite{3-4} proved that for each rational number
$rin[3,4]$, there exists a planar graph $G$ with $chi_c(G)=r$.
Moser''s and Zhu''s proofs are quite complicated. Our construction
is conceptually simpler. Moreover, for $ngeq 5$, $K_n$-minor
free graphs, including the planar graphs are constructed with a
unified method.
For $K_4$-minor free graphs, although Hell and Zhu cite{hz98}
proved that there is no $K_4$-minor free graph $G$ with
$chi_c(G)in (8/3,3)$. The question whether there exists a
$K_4$-minor free graph $G$ with $chi_c(G)=r$ for each rational
number $rin[2,8/3]$ remained open. This thesis solves this
problem: For each rational number $rin[2,8/3]$, we shall
construct a $K_4$-minor free $G$ with $chi_c(G)=r$.
This thesis also studies the relation between the circular
chromatic number and the girth of $K_4$-minor free graphs. For
each integer $n$, the supremum of the circular chromatic number of
$K_4$-minor free graphs of odd girth (the length of shortest odd
cycle) at least $n$ is determined. It is also proved that the
same bound is sharp for $K_4$-minor free graphs of girth $n$.
By a classical result of ErdH{o}s, for any positive integers $l$
and $n$, there exists a graph $G$ of girth at least $l$ and of
chromatic number $n$. Using probabilistic method, Zhu
cite{unique} proved that for each integer $l$ and each rational
number $rgeq 2$, there is a graph $G$ of girth at least $l$ such
that $chi_c(G)=r$. Construction of such graphs for $rgeq 3$ was
given by Nev{s}etv{r}il and Zhu cite{nz}. The question of how
to construct large girth graph $G$ with $chi_c(G)=r$ for given
$rin(2,3)$ remained open. In this thesis, we present a unified
method that constructs, for any $rgeq 2$, a graph $G$ of girth
at least $l$ with circular chromatic number $chi_c(G) =r$.
Graphs $G$ with $chi_c(G)=chi(G)$ have been studied extensively
in the literature. Many families of graphs $G$ are known to
satisfy $chi_c(G)=chi(G)$. However it remained as an open
question as how to construct arbitrarily large $chi$-critical
graphs $G$ of bounded maximum degree with $chi_c(G)=chi(G)$.
This thesis presents a construction of such graphs.
The circular flow number $Phi_c(G)$ is the dual concept of
$chi_c(G)$. Let $G$ be a graph. Replace each edge $e=xy$ by a
pair of opposite arcs $a=overrightarrow{xy}$ and
$a^{-1}=overrightarrow{yx}$. We obtain a symmetric directed
graph. Denote by $A(G)$ the set of all arcs of $G$. A chain is a
mapping $f:A(G)
ightarrow I!!R$ such that for each arc $a$,
$f(a^{-1})=-f(a)$. A flow is a chain such that for each subset
$X$ of $V(G)$, $sum_{ain[X, ar{X}]}f(a)=0$, where
$[X, ar{X}]$ is the set of all arcs from $X$ to $V-X$. An
$r$-flow is a flow such that for any arc $ain A(G)$ , $1leq
|f(a)| leq r-1$. The circular flow number of $G$ is
$Phi_c(G)=mbox{ inf}{r: G mbox{ admits a } rmbox{-flow}}$.
It was conjectured by Tutte that every graph $G$ has
$Phi_c(G)leq 5$. By taking the geometrical dual of planar
graphs, Moser''s and Zhu''s results concerning circular chromatic
numbers of planar graphs imply that for each rational number
$rin[2,4]$, there is a graph $G$ with $Phi_c(G)=r$. The question
remained open whether for each $rin(4,5)$, there exists a graph
$G$ with $Phi_c(G)=r$. In this thesis, for each rational number
$rin [4,5]$, we construct a graph $G$ with $Phi_c(G)=r$.
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Ko, Chun Jen, and 柯淳仁. "Jet flow of a circular pipe leakage." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/75122647769190303595.
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碩士<br>國立屏東科技大學<br>車輛工程系所<br>104<br>This thesis simulates water jet flow passes through one or two holes on a circular pipe. The main objective of this study is to identify the combination of parameters that greatly influence the magnitude of pressure difference across the hole. In the beginning, the Taguchi L9 (43) orthogonal table was selected because of the four parameters to be investigated. They are the pipe thickness, the pipe diameter, the hole size, and the hole divergence angle. There are three levels associated to each of the parameter. Once the nine cases were setup, Solidworks was used to draw the geometry of the nine models. After that, the models were imported into the Gambit for mesh construction before simulations were performed using Fluent. The values of the pressure were normalized to yield dimensionless pressure. Optimization processes based on Taguchi Method’s “Larger-the-Better” and “Smaller-the-Better” were employed to determine the corresponding proper combinations of the four parameters. These combinations were later successfully examined. For the models, it was found that the divergence angle of the hole has the greatest influence on the pressure difference followed by the hole diameter. Results showed that a divergence angle of 10° yielded the greatest pressure drop while a divergence angle of 0° yielded the least.
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Tsuei, Hi En, and 崔海恩. "The Flow Interference between Two Circular Cylinders." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/60832486156815828056.
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KE, ZHI-XIAN, and 柯志賢. "Locally conical flow simulation of three dimensional vortical flow around circular cones." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/76389407559452622993.
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Vo, Ngoc Diep. "Characteristics of curvilinear flow past circular-crested weirs." Thesis, 1992. http://spectrum.library.concordia.ca/2683/1/NN80996.pdf.
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Wen, Sheng-yu, and 溫晟淯. "Noise Analysis of Flow Over A Circular Cylinder." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/51067468286853401737.
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碩士<br>國立成功大學<br>航空太空工程學系<br>85<br>The major topic is to use numerical approach to simulate noise
generated by flow past a blunt body.A two-dimensional circular
cylinder is selected as our physical model.The far-field
pressure distribution and the corresponding Fourier Spectra are
analyzed.Moreover,the effects included various Mach number and
Reynolds number are considered in the research.In the whole
problem,we adapt an Upwind finitefinite volume method of third
order accuracy and a three-stage Runge-Kutta time integration
method of second order accuracy .Finally,we concentrate in the
noise generatedin the flow field,Kirchhoff integral is used here
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Ling, Yaw-Dongg, and 林耀東. "Simulations of Turbulent Flow Over a Circular Cylinder." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/54232860832763233760.
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碩士<br>國立臺灣大學<br>機械工程研究所<br>81<br>The flow over a circular cylinder is simulated for low Reynolds
of Launder and Sharma, and that of Lam and Bremhorst is also
paper discusses the influence of adjusting the turbulenthe
correlation between separation angle and terms in the turbulent
equation. The additional L.epsilon. term in the turbulent rate
equation makes the distribution of k along the radial not match
with the wall function theory. It seems to be better to
constant to correct the overestimation of k. Decreasingve is
more influential on flow indicators than increasing it, and C.
epsilon.2 is more influential on flow indicators thanIn LS
model, C.epsilon.1 is more sensible on this flow field than C.
epsilon.2. In the turbulent kinetic energy equation, diffusion
best correlated with separation angle, and the production term
is
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Tseng, Ching-Chi, and 曾慶祺. "Enhancement of Heat Transfer in Circular Tube Flow." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/09104198612537846705.
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