Dissertations / Theses: 'Flow geometries'

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Moore, Jennifer Anne. "Computational blood flow modelling in realistic arterial geometries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/NQ35257.pdf.

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Wang, Yechun. "Numerical studies of stokes flow in confined geometries." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2115.

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Thesis (M.S.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Dept. of Chemical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Sopko, James J. "Modeling fluid flow by exploring different flow geometries and effect of weak compressibility." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FSopko.pdf.

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Vlachos, Nickolas Dimitris. "Boundary element method of incompressible flow past deforming geometries." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297802.

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Chen, Li-Kwen. "Unsteady flow and heat transfer in periodic complex geometries for the transitional flow regime." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Chen_09007dcc804bed71.pdf.

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Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 12, 2008) Includes bibliographical references.

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Tysell, Lars. "Hybrid Grid Generation for Viscous Flow Computations Around Complex Geometries." Doctoral thesis, KTH, Mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11934.

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A set of algorithms building a program package for the generation of twoandthree-dimensional unstructured/hybrid grids around complex geometrieshas been developed. The unstructured part of the grid generator is based on the advancing frontalgorithm. Tetrahedra of variable size, as well as directionally stretched tetrahedracan be generated by specification of a proper background grid, initiallygenerated by a Delaunay algorithm. A marching layer prismatic grid generation algorithm has been developedfor the generation of grids for viscous flows. The algorithm is able to handleregions of narrow gaps, as well as concave regions. The body surface is describedby a triangular unstructured surface grid. The subsequent grid layers in theprismatic grid are marched away from the body by an algebraic procedurecombined with an optimization procedure, resulting in a semi-structured gridof prismatic cells. Adaptive computations using remeshing have been done with use of a gradientsensor. Several key-variables can be monitored simultaneously. The sensorindicates that only the key-variables with the largest gradients give a substantialcontribution to the sensor. The sensor gives directionally stretched grids. An algorithm for the surface definition of curved surfaces using a biharmonicequation has been developed. This representation of the surface canbe used both for projection of the new surface nodes in h-refinement, and theinitial generation of the surface grid. For unsteady flows an algorithm has been developed for the deformationof hybrid grids, based on the solution of the biharmonic equation for the deformationfield. The main advantage of the grid deformation algorithm is that itcan handle large deformations. It also produces a smooth deformation distributionfor cells which are very skewed or stretched. This is necessary in orderto handle the very thin cells in the prismatic layers. The algorithms have been applied to complex three-dimensional geometries,and the influence of the grid quality on the accuracy for a finite volumeflow solver has been studied for some simpler generic geometries.
QC 20100812

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Gong, Jing. "Hybrid Methods for Unsteady Fluid Flow Problems in Complex Geometries." Doctoral thesis, Uppsala universitet, Avdelningen för teknisk databehandling, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8341.

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In this thesis, stable and efficient hybrid methods which combine high order finite difference methods and unstructured finite volume methods for time-dependent initial boundary value problems have been developed. The hybrid methods make it possible to combine the efficiency of the finite difference method and the flexibility of the finite volume method. We carry out a detailed analysis of the stability of the hybrid methods, and in particular the stability of interface treatments between structured and unstructured blocks. Both the methods employ so called summation-by-parts operators and impose boundary and interface conditions weakly, which lead to an energy estimate and stability. We have constructed and analyzed first-, second- and fourth-order Laplacian based artificial dissipation operators for finite volume methods on unstructured grids. The first-order artificial dissipation can handle shock waves, and the fourth-order artificial dissipation eliminates non-physical numerical oscillations efficiently. A stable hybrid method for hyperbolic problems has been developed. It is shown that the stability at the interface can be obtained by modifying the dual grid of the unstructured finite volume method close to the interface. The hybrid method is applied to the Euler equation by the coupling of two stand-alone CFD codes. Since the coupling is administered by a third separate coupling code, the hybrid method allows for individual development of the stand-alone codes. It is shown that the hybrid method is an accurate, efficient and practically useful computational tool that can handle complex geometries and wave propagation phenomena. Stable and accurate interface treatments for the linear advection–diffusion equation have been studied. Accurate high-order calculation are achieved in multiple blocks with interfaces. Three stable interface procedures — the Baumann–Oden method, the “borrowing” method and the local discontinuous Galerkin method, have been investigated. The analysis shows that only minor differences separate the different interface handling procedures. A conservative stable and efficient hybrid method for a parabolic model problem has been developed. The hybrid method has been applied to the full Navier–Stokes equations. The numerical experiments support the theoretical conclusions and show that the interface coupling is stable and converges at the correct order for the Navier–Stokes equations.

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Dröge, Marc Theodoor. "Cartesian grid methods for turbulent flow simulation in complex geometries." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2006. http://irs.ub.rug.nl/ppn/298825759.

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Clayton, David James. "Large eddy simulation of non-premixed flow in complex geometries." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428760.

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RONZANI, ERNESTO RIBEIRO. "NUMERICAL SOLUTION OF COMPRESSIBLE AND INCOMPRESSIBLE FLOW IN IRREGULAR GEOMETRIES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18648@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho propõe um método numérico de solução de escoamentos de fluidos compressíveis e incompressíveis a qualquer número de Mach em geometrias irregulares. Um sistema bidimensional de coordenadas curvilíneas não-ortogonais,coincidentes com os contornos físicos é utilizado. Os componentes cartesianos de velocidade são usados nas equações da quantidade de movimento e os covariantes na equação da continuidade. Seleciona-se a técnica de volumes finitos para discretizar as equações de conservação relacionadas aos princípios físicos, em regime permanente devido esta preservar a propriedade conservativa das equações e a sua con sistência física no processo numérico. Adota-se a configuração de malha co-localizada, avaliando-se todas as variáveis dependentes nos pontos centrais dos volumes são avaliados com esquemas Power-Law e Quick. Especial atenção é dada ao tratamento numérico das condições de contorno. O problema do acoplamento massa específica-pressão-velocidade é solucionado usando-se uma combinação das equações da continuidade, de quantidade de movimento linear e de uma equação de estado, gerando duas equações de correção da pressão. A primeira corrige a massa específica e a pressão, a segunda, o fluxo de massa e a velocidade. Propõe-se uma modificação da equação da correção da velocidade usando um termo de compensação do erro obtido na sua avaliação a fim de acelerar a convergência. Utilizam-se vários tipos de interpolação da massa específica na face, para minimizar as atenuações das variáveis, causadas pela falsa difusão. Para a solução das equações algébricas resultantes usa-se o algoritmo TDMA linha por linha e um processo de correção por blocos para acelerar a convergência. O método proposto é verificado em seis problemas testes, através da comparação com os resultados analíticos e numéricos disponíveis na literatura.
The present work consists in the development of a numerical method of solution of compressible and incompressible fluid flow for all speed in iregular geometries. A boundary-fitted two-dimensional nonorthogonal curvilinear coordinate systeam is utilized. The cartesian velocity components are the dependent variables in the momentum equations and covariant velocity components are used in the continuity equation. The finite-volume technique was selected to discretuze the steady-state physical phenomenon conservation equations, since this method keeps the conservative property of the equations and its physical consistency in the numerical process. A nonstaggered grid was employed, and all dependent variables are evaluated at the cell center points, which divides the physical domain. The convection-diffusion fluxes at the control volumes faces are evaluated with the Power Law and Quick shemes. Special attention is paid to the numerical treatment of boundary conditions. The problem of velocity-pressure-density coupling is solved using a combination of continuity, momentum equations and state equation resulting in two pressure correction equations. The first equation corrects the density and the pressure, the second equation corrects the mass flux and the velocity. A modification in the velocity correction equations is proposed using a compensationterm to accelerate the convergence. Several types of interpolation of the face density are used to reduce variable atenuations, caused by false diffusion. For the solution of the resulting algebric equations,the line-by-line TDMA algorith is used as well as a block-correction method to accelerate the convergence. The proposed method is verified on six test problems,by comparing the present results with analytical and numerical results avaiable in the literature.

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Havard, Stephen Paul. "Numerical simulation of non-Newtonian fluid flow in mixing geometries." Thesis, University of South Wales, 1989. https://pure.southwales.ac.uk/en/studentthesis/numerical-simulation-of-nonnewtonian-fluid-flow-in-mixing-geometries(eaee66ae-2e3d-44ba-9a5f-41d438749534).html.

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In this thesis, a theoretical investigation is undertaken into fluid and mixing flows generated by various geometries for Newtonian and non-Newtonian fluids, on both sequential and parallel computer systems. The thesis begins by giving the necessary background to the mixing process and a summary of the fundamental characteristics of parallel architecture machines. This is followed by a literature review which covers accomplished work in mixing flows, numerical methods employed to simulate fluid mechanics problems and also a review of relevant parallel algorithms. Next, an overview is given of the numerical methods that have been reviewed, discussing the advantages and disadvantages of the different methods. In the first section of the work the implementation of the primitive variable finite element method to solve a simple two dimensional fluid flow problem is studied. For the same geometry colour band mixing is also investigated. Further investigational work is undertaken into the flows generated by various rotors for both Newtonian and non-Newtonian fluids. An extended version of the primitive variable formulation is employed, colour band mixing is also carried out on two of these geometries. The latter work is carried out on a parallel architecture machine. The design specifications of a parallel algorithm for a MIMD system are discussed, with particular emphasis placed on frontal and multifrontal methods. This is followed by an explanation of the implementation of the proposed parallel algorithm, applied to the same fluid flow problems as considered earlier and a discussion of the efficiency of the system is given. Finally, a discussion of the conclusions of the entire accomplished work is presented. A number of suggestions for future work are also given. Three published papers relating to the work carried out on the transputer networks are included in the appendices.

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Raeisi, Dehkordi Amir Hooshang. "Investigation of flow boiling phenomena in small-scale complex geometries." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2531.

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This study concerns measurement and prediction of single-phase and flow boiling heat transfer coefficients and pressure drops in mini multi-channel geometries with and without interconnecting passages, including plate channel; parallel channel; in-line pin-fin and in-line off-set pin-fin surfaces. Experiments were performed with refrigerant R113 and deionised water at atmospheric pressure. Single-phase and flow boiling heat transfer coefficients and pressure drops were obtained over a range of effective heat fluxes and mass fluxes. For the plate and parallel channel surfaces, the results obtained have been compared with several published macro- and micro-channels correlations. For the in-line and in-line off-set pin fin surfaces, as the geometries have some similarities with tube bundles, the results obtained have been predicted using the standard correlations for tube bundles. The results also have been compared with several existing correlations developed based on macro-scale tube bundles and micro-pin-fin surfaces data. The saturated flow boiling heat transfer coefficients for the parallel channel and pin-fin surfaces were similar to within the experimental uncertainty, and considerably higher than the plate channel values, all dependent on heat flux and reasonably independent of mass flux and vapour mass fraction. This indicated that the dominant heat-transfer mechanism in the saturated boiling flow regime was nucleate boiling for all surfaces. The parallel channel, in-line and off-set pin-fin surfaces improved heat transfer by increasing the surface area and the heat transfer coefficient in comparison with the plate channel surface. The two-phase pressure drops in the parallel channel and pin-fin surfaces were considerably larger than that for the plate channel surface. Thus, the reduction in wall temperature is achieved by a significant pressure drop penalty. For the pin-fin surfaces, at low vapour qualities the heat transfer coefficients were in reasonable agreement with the conventional scale tube bundles correlations however as the vapour quality increases, the correlations were not able to predict the heat transfer coefficient as unlike the conventionally-sized tube bundles, the convective enhancement does not happen in the mini-pin-fin surfaces tested. The nucleate pool boiling correlation of Cooper (1984) provided a good agreement with the data for all surfaces tests with R113 and deionised water. The measured two-phase pressure drops for both pin-fin surfaces tests with R113 and deionised water were in a good agreement with the predicted values obtained from standard correlations for tube bundles, indicating pressure drop methods maybe transferable.

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Tang, Hansong. "Numerical simulation of unsteady three dimensional incompressible flows in complex geometries." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19324.

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Komminaho, Jukka. "Direct numerical simulation of turbulent flow in plane and cylindrical geometries." Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3054.

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Prakash, Sujata. "Adaptive mesh refinement for finite element flow modeling in complex geometries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/NQ45746.pdf.

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Lorenzi, Massimo. "X-ray computed microtomography applications for complex geometries and multiphase flow." Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/19794/.

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In all fields, fundamental and applied research seek to produce experimental measurements without causing interferences to the process being observed. This capability is of paramount importance, since small perturbations of the phenomenon can alter it to the point of producing biased or even incorrect results. Xray techniques, based on synchrotron or laboratory X-ray sources, have attracted the attention of the research and industrial R&D community thanks to their characteristic of having little to no detectable influence on the subject under study. Moreover, if declined as tomography, this technique can provide localized full volume information at the micrometre scale, from which arbitrary shaped geometries and material densities can be deduced. During this thesis an X-ray microtomography instrument, based on a laboratory X-ray source, has been exploited to gain three main objectives. The first one is the analysis of how a liquid drop, of water or glycol, adapts its shape to reach an equilibrium state when gently deposed on a flat or patterned surface. So far this has been done using 2D techniques but introducing the knowledge of the third dimension and being able to see the drop shape even in not optically accessible locations, opens new possibilities to better understand the physics that regulate it. The second one is the reconstruction of the internal geometries of automotive diesel injectors with high resolution to detect and highlight differences between nominal and real geometries, key information to produce more realistic CFD simulations of the flow inside production grade injectors geometries. A scaled -up model made of PEEK was also studied, producing successive tomographies, to detect small geometrical changes induced by part usage, giving an in-depth view of the locations more prone to be damaged by cavitation flow. The third one is the study of a multiphase flow inside the same scaled-up model injection channel with flowing conditions exhibiting cavitation. The geometry of the non-axisymmetric model mimics the flow pattern of a real diesel injection channel and automotive grade diesel was consequently selected as fluid. Understanding the dependence of cavitation development on flow characteristics in a three-dimensional way, through the determination of the localized void fraction of the multiphase flow, can lead to improvements in the knowledge of such a phenomenon that can guide the design of future fuel injection equipment.

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Ellul, Ivor Raymond. "The prediction of dispersed gas-liquid flow in complex pipe geometries." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47422.

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Keegan, Fiona. "Experimental investigation into non-Newtonian fluid flow through gradual contraction geometries." Thesis, University of Liverpool, 2009. http://livrepository.liverpool.ac.uk/1293/.

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This thesis presents the results of an investigation into the flow of several non- Newtonian fluids through two curved gradual planar contractions (contraction ratios 8:1 and 4:1). The objectives were to determine whether a newly discovered effect (velocity overshoots were observed in the flow of a 0.05% polyacrylamide solution close to the sidewalls of a gradual contraction followed by a sudden expansion by Poole et al., 2005) could be reproduced in the absence of the expansion, learn more about the phenomenon and to provide a comprehensive set of experimental results for numerical modellers to compare their results to. The fluids investigated were a Newtonian control fluid (a glycerine-water mixture), four concentrations of polyacrylamide (PAA), varying from the ‘dilute’ range to the ‘semi-dilute’ range and two concentrations of xanthan gum (XG), both in the ‘semi- dilute’ range. All fluids were characterised using shear rheology techniques and where possible extensional rheology measurements were also undertaken. The fluid properties determined from this characterisation were used to estimate various non- dimensional numbers such as the Reynolds and Deborah numbers, which can then be used to characterise the flow. The flow under investigation was the flow through a gradual contraction section. Two smooth curved planar gradual contractions were used with contraction ratios of 8:1 and 4:1. The upstream internal duct dimensions were 80mm by 80mm in both cases and the downstream internal duct dimensions were 80mm by 10mm for the 8:1 contraction and 80mm by 20mm for the 4:1 contraction. Polymer degradation within the test rig was assessed and the maximum time that the solutions could be reliably used was found to be six hours. The fluid velocity was measured at discrete locations within the flow using laser Doppler anemometry (LDA), which is a non-intrusive flow measurement technique. Measurements were taken across the XZ-centreplane (side to side) and in some cases across the XY-centreplane (top to bottom). The flow of the Newtonian control fluid was as expected with the flow flattening into the ‘top hat’ shape usually observed in Newtonian flow through a gradual contraction (as utilised in wind tunnel design for example). The flows of 0.01% PAA (‘dilute’) and 0.07% XG (‘semi-dilute’) also flattened as the flow progressed through the 8:1 contraction as the Deborah numbers in these flows were very low. Velocity overshoots close to the plane sidewalls were observed in both the 0.03% and 0.05% PAA solutions through the 8:1 and 4:1 contractions. The overshoots through both contractions seemed to be influenced most by the Deborah number (i.e. the extensional properties of the flow and fluid). Velocity overshoots were observed in the 0.3% PAA solution through both contractions but they were different in shape to those seen at the lower concentrations. The overshoots were closer to the centre of the flow growing into one large ‘overshoot’ at the end of the contraction. This investigation showed that the velocity overshoots can be reproduced in both the 8:1 and 4:1 gradual contraction in several concentrations of PAA providing the right parameters are met (i.e. fluid properties, flow rate etc.). Good quality sets of data have been produced, which can be used in the future by researchers interested in numerical modelling of non-Newtonian fluid flows through similar contractions.

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Putivisutisak, Sompong. "Computation of heat transfer and flow in compact heat-exchanger geometries." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8536.

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Liss, Dirk. "Emplacement processes and magma flow geometries of the Whin Sill complex." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403441.

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The emplacement processes of the Whin Sill complex and its associated dykes have been studied using a combined approach of detailed field and magnetic investigations. Regional palaeodirectionai results show two different but consistent palaeomagnetic signatures and allow the sill complex to be subdivided into three geographically separate intrusions: the 'Holy Island Sill', the 'Alnwick Sill' and the ' Hadrian's Wall-Pennine Sill', The Little Whin Sill has been identified previously as a fourth, separate sill on petrological evidence. On the basis of the palaeodirectional results it is also possible to relate the exposed contemporaneous dykes to the individual intrusions. The magma flow geometries within the individual Whin Sill intrusions were detennined by AMS analyses, and both traditional and newly identified magma flow indicators. For the Holy Island Sill the results suggest that the magma flow was homogeneously southwards directed and that the Holy Island Dyke acted as the feeder to this intrusion. In the Alnwick Sill the magma flow was homogeneously westwards directed and it is proposeU that an offshore, en echelon segment of the High Green Dyke fed the Alnwick Sill. The magma flow geometry for the Hadrian's Wall-Pennine Sill is complex. The results suggest that this intrusion was fed by the Hett Dyke and that the magma flow within the sill was generally north and north westwards directed. It is proposed that the intrusion was emplaced during a phase of late Variscan, E-W compression and that pre-existing faults at a high angle to this compression direction acted as a magma flow barrier along which the magma became deflected. The geometry of the sills is approximately that of a quarter- to half-saucer-shape, with the dykes being situated at the saucer truncation. From the feeder dykes magma was injected into the individual sill bodies and the magma flow was generally up dip or parallel to the strike of the host rock bedding, thus out of the basin centres and into levels of lower lithospheric pressure. It is proposed that a compressional stress field and locally overpressured horizons had a significant impact on the initiation and emplacement of the Whin Sill complex.

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Scelsi, Lino. "Experimental observation and numerical prediction of flow-induced crystallisation for polymer melts within complex flow geometries." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611551.

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Rajamani, Bharanidharan. "Composite Solution Technique for Efficient Simulation of Incompressible Flow in Complex 2-D AND Axisymmetric Geometries." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1030031668.

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Rincon, Alberto. "Transient simulation of non-Newtonian coextrusion flows in complex geometries /." *McMaster only, 1998.

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Stålberg, Erik. "A high order method for simulation of fluid flow in complex geometries." Licentiate thesis, KTH, Mechanics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-322.

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A numerical high order difference method is developed for solution of the incompressible Navier-Stokes equations. The solution is determined on a staggered curvilinear grid in two dimensions and by a Fourier expansion in the third dimension. The description in curvilinear body-fitted coordinates is obtained by an orthogonal mapping of the equations to a rectangular grid where space derivatives are determined by compact fourth order approximations. The time derivative is discretized with a second order backward difference method in a semi-implicit scheme, where the nonlinear terms are linearly extrapolated with second order accuracy.

An approximate block factorization technique is used in an iterative scheme to solve the large linear system resulting from the discretization in each time step. The solver algorithm consists of a combination of outer and inner iterations. An outer iteration step involves the solution of two sub-systems, one for prediction of the velocities and one for solution of the pressure. No boundary conditions for the intermediate variables in the splitting are needed and second order time accurate pressure solutions can be obtained.

The method has experimentally been validated in earlier studies. Here it is validated for flow past a circular cylinder as an example of a physical test case and the fourth order method is shown to be efficient in terms of grid resolution. The method is applied to external flow past a parabolic body and internal flow in an asymmetric diffuser in order to investigate the performance in two different curvilinear geometries and to give directions for future development of the method. It is concluded that the novel formulation of boundary conditions need further investigation.

A new iterative solution method for prediction of velocities allows for larger time steps due to less restrictive convergence constraints.

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Stålberg, Erik. "A high order method for simulation of fluid flow in complex geometries /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-322.

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Lucente, Carlin Miller. "COMPUTATIONAL ANALYSES FOR FLUID FLOW AND HEAT TRANSFER IN DIFFERENT CURVED GEOMETRIES." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1337176681.

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Israel, Daniel Morris. "A New Approach for Turbulent Simulations in Complex Geometries." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1272%5F1%5Fm.pdf&type=application/pdf.

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Dean, Brian D. "The Effect of Shark Skin Inspired Riblet Geometries on Drag in Rectangular Duct Flow." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1311874211.

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Blockley, Edward William. "Nonlinear solutions of the amplitude equations governing fluid flow in rotating spherical geometries." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/41950.

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We are interested in the onset of instability of the axisymmetric flow between two concentric spherical shells that differentially rotate about a common axis in the narrow-gap limit. The expected mode of instability takes the form of roughly square axisymmetric Taylor vortices which arise in the vicinity of the equator and are modulated on a latitudinal length scale large compared to the gap width but small compared to the shell radii. At the heart of the difficulties faced is the presence of phase mixing in the system, characterised by a non-zero frequency gradient at the equator and the tendency for vortices located off the equator to oscillate. This mechanism serves to enhance viscous dissipation in the fluid with the effect that the amplitude of any initial disturbance generated at onset is ultimately driven to zero. In this thesis we study a complex Ginzburg-Landau equation derived from the weakly nonlinear analysis of Harris, Bassom and Soward [D. Harris, A. P. Bassom, A. M. Soward, Global bifurcation to travelling waves with application to narrow gap spherical Couette flow, Physica D 177 (2003) p. 122-174] (referred to as HBS) to govern the amplitude modulation of Taylor vortex disturbances in the vicinity of the equator. This equation was developed in a regime that requires the angular velocities of the bounding spheres to be very close. When the spherical shells do not co-rotate, it has the remarkable property that the linearised form of the equation has no non-trivial neutral modes. Furthermore no steady solutions to the nonlinear equation have been found. Despite these challenges Bassom and Soward [A. P. Bassom, A. M. Soward, On finite amplitude subcritical instability in narrow-gap spherical Couette flow, J. Fluid Mech. 499 (2004) p. 277-314] (referred to as BS) identified solutions to the equation in the form of pulse-trains. These pulse-trains consist of oscillatory finite amplitude solutions expressed in terms of a single complex amplitude localised as a pulse about the origin. Each pulse oscillates at a frequency proportional to its distance from the equatorial plane and the whole pulse-train is modulated under an envelope and drifts away from the equator at a relatively slow speed. The survival of the pulse-train depends upon the nonlinear mutual-interaction of close neighbours; as the absence of steady solutions suggests, self-interaction is inadequate. Though we report new solutions to the HBS co-rotation model the primary focus in this work is the physically more interesting case when the shell velocities are far from close. More specifically we concentrate on the investigation of BS-style pulse-train solutions and, in the first part of this thesis, develop a generic framework for the identification and classification of pulse-train solutions. Motivated by relaxation oscillations identified by Cole [S. J. Cole, Nonlinear rapidly rotating spherical convection, Ph.D. thesis, University of Exeter (2004)] whilst studying the related problem of thermal convection in a rapidly rotating self-gravitating sphere, we extend the HBS equation in the second part of this work. A model system is developed which captures many of the essential features exhibited by Cole's, much more complicated, system of equations. We successfully reproduce relaxation oscillations in this extended HBS model and document the solution as it undergoes a series of interesting bifurcations.

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Qin, Tongran. "Buoyancy-thermocapillary convection of volatile fluids in confined and sealed geometries." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54939.

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Convection in a layer of fluid with a free surface due to a combination of thermocapillary stresses and buoyancy is a classic problem of fluid mechanics. It has attracted increasing attentions recently due to its relevance for two-phase cooling. Many of the modern thermal management technologies exploit the large latent heats associated with phase change at the interface of volatile liquids, allowing compact devices to handle very high heat fluxes. To enhance phase change, such cooling devices usually employ a sealed cavity from which almost all noncondensable gases, such as air, have been evacuated. Heating one end of the cavity, and cooling the other, establishes a horizontal temperature gradient that drives the flow of the coolant. Although such flows have been studied extensively at atmospheric conditions, our fundamental understanding of the heat and mass transport for volatile fluids at reduced pressures remains limited. A comprehensive and quantitative numerical model of two-phase buoyancy-thermocapillary convection of confined volatile fluids subject to a horizontal temperature gradient has been developed, implemented, and validated against experiments as a part of this thesis research. Unlike previous simplified models used in the field, this new model incorporates a complete description of the momentum, mass, and heat transport in both the liquid and the gas phase, as well as phase change across the entire liquid-gas interface. Numerical simulations were used to improve our fundamental understanding of the importance of various physical effects (buoyancy, thermocapillary stresses, wetting properties of the liquid, etc.) on confined two-phase flows. In particular, the effect of noncondensables (air) was investigated by varying their average concentration from that corresponding to ambient conditions to zero, in which case the gas phase becomes a pure vapor. It was found that the composition of the gas phase has a crucial impact on heat and mass transport as well as on the flow stability. A simplified theoretical description of the flow and its stability was developed and used to explain many features of the numerical solutions and experimental observations that were not well understood previously. In particular, an analytical solution for the base return flow in the liquid layer was extended to the gas phase, justifying the previous ad-hoc assumption of the linear interfacial temperature profile. Linear stability analysis of this two-layer solution was also performed. It was found that as the concentration of noncondensables decreases, the instability responsible for the emergence of a convective pattern is delayed, which is mainly due to the enhancement of phase change. Finally, a simplified transport model was developed for heat pipes with wicks or microchannels that gives a closed-form analytical prediction for the heat transfer coefficient and the optimal size of the pores of the wick (or the width of the microchannels).

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Varela, Ballesta Sylvana Verónica. "Computational and experimental modeling of fluid flow and heat transfer processes in complex geometries." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/80717.

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El objetivo principal de este trabajo es el estudio numérico (caffa3d.MB) y experimental (PIV) de los campos de velocidad y de temperatura en dominios complejos como los encontrados en las computadoras u otros sistemas electrónicos refrigerados que contengan circuitos impresos (PCB, Printed Circuit Board). La refrigeración es uno de los principales desafíos que estos dispositivos se deben tratar. La disipación del calor de los dispositivos de circuitos electrónicos se ha convertido en una cuestión importante a tener en cuenta durante su diseño. Los PCB son circuitos electrónicos que generan calor por efecto Joule y necesitan ser enfriados. Son cada vez más pequeños y por lo tanto los problemas del calentamiento disminuyen su eficiencia y vida útil. El estudio de la velocidad y los campos de temperatura está estrechamente relacionada con el análisis de la evolución espacial y temporal de las estructuras de flujo que se encuentran en las cavidades cerradas que contiene PCB y con el entendimiento de la influencia de la geometría, la velocidad de entrada de fluido y temperatura de la placa en el proceso de enfriamiento del PCB.
The main objective of this work is the numerical (caffa3d.MB) and experimental (PIV) study of the velocity and temperature fields in complex domains like those encountered in computers or other electronic refrigerated systems with printed circuit board (PCB). Cooling is one of the main challenges these devices have to deal with. Heat removal from the electronic circuit devices has become an important issue to take into account during their design. PCB's are electronic circuits that generate heat by Joule effect and need to be cooled down. They are becoming smaller and therefore some warming problems appear that lowers their efficiency and lifespan. The study of the velocity and temperature fields is closely connected with the analysis of the spatial and temporal evolution of the flow structures found in PCB enclosed cavities and with the understanding of the influence of the geometry, the inlet fluid velocity and plate temperature in the cooling process of the PCB.

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Memon, M. D. "Numerical modelling and prediction of fluid flow and heat transfer in rotating disc geometries." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484071.

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Amin, Abolfazl. "Three-Dimensional Numerical Simulations of Liquid Laminar Flow Over Superhydrophobic Surfaces with Post Geometries." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2634.

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Frictional resistance reduction of liquid flow over surfaces has recently become a more important topic of research in the field of fluid dynamics. Scientific and technological progress and continued interest in nano and micro-technology have required new developments and approaches related to reducing frictional resistance, especially in liquid flow through nano and micro-channels. The application of superhydrophobic surfaces could be very effective in achieving the desired flow through such small channels. Superhydrophobic surfaces are created by intentionally creating roughnesses on the surface and applying a uniform hydrophobic coating to the entire surface. Liquid droplet tests have revealed that because of the trapped air within the cavities such surfaces could have contact angles as high as 179°. Such a property gives superhydrophobic surfaces liquid repelling characteristics making them very suitable for frictional resistance reduction in liquid flow through nano or micro-channels, provided wetting of the cavities could be avoided. This study presents 3-D numerical simulation results of liquid laminar flow over post patterned superhydrophobic surfaces. The research was performed in three phases, 1) pressure-driven flow with square micro-posts, 2) Couette flow with square micro-posts, and 3) pressure-driven flow with rectangular micro-posts at various aspect ratios. In phases (1) and (2) the influences of important parameters such as the cavity fraction, in the range of 0.0-0.9998, and the relative module width, from 0.01 to 1.5, on frictional resistance reduction in the creeping flow regime were explored. Phase (1) also addressed the effect of varying Reynolds number from 1 to 2500 on frictional resistance. Phase (3) was conducted for aspect ratios of 1/8, 1/4, 1/2, 2, 4, and 8 also in the creeping flow regime. The obtained results suggest that important parameters such as cavity fraction (relative area of the cavities), relative module width (combined post and cavity width relative to the channel hydraulic diameter), and the Reynolds number have great influence on the frictional resistance reduction. For pressure-driven flow at cavity fraction 0.9998, reductions as high as 97% in the frictional resistance were predicted compared with the classical channel flow. This reduction is directly related to the significant reduction in liquid-solid contact area. With respect to the effect of relative module width on the overall frictional resistance, a reduction of 93% in the frictional resistance was observed as the relative module width was increased from 0.1 to 1.5. This is indicative of the importance of the relative spacing size of the posts/cavities compared to the channel size in micro-channel liquid flow. The overall frictional resistance for post-patterned superhydrophobic surfaces was found to be independent of the Reynolds number up to a value of nominally 40 after which the non-dimensional frictional resistance increased at high values of the Reynolds number. However, at very high cavity fractions the frictional resistance was independent of Reynolds number only up to about 4. When the driving mechanism was a Couette flow, similar to the pressure-driven flow, as the cavity fraction and the relative module width increased the frictional resistance on the superhydrophobic surface decreased. At a cavity fraction of 0.9998 the reduction in the non-dimensional frictional resistance was approximately 96%, which was only 1% different from the similar pressure-driven scenario. However, a more significant difference was observed between the slip velocities for the two flow types, and it was determined that the pressure-driven flow resulted in greater apparent slip velocities than Couette flow. A maximum difference in normalized slip between the two scenarios of approximately 20% was obtained at relative module width 0.1 and Reynolds number 1. Results for superhydrophobic surfaces with rectangular micro-posts approached those reported in the literature for micro-ribs as the aspect ratio of the posts increased. When the flow was perpendicular to the long side of the posts, and as the aspect ratio increased, the frictional resistance approached previously published transverse rib results. Similarly, when the liquid flow direction was parallel to the long side of the posts, the frictional resistance results also approached those of the previously published longitudinal ribs as the aspect ratio increased.

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Rock, Ross C. K. "A numerical investigation of turbulent interchange mixing of axial coolant flow in rod bundle geometries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0005/MQ40977.pdf.

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Lee, Kyung Eun. "The effect of geometrical configurations on physiological pulsatile flow in ideal and realistic vessel geometries." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485736.

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Owen, Joshua James. "Erosion-corrosion of carbon steel in complex flow geometries in oil & gas CO2 environments." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/21507/.

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When sand is present in carbon dioxide (CO2) corrosion environments in oil and gas pipe flow, wear rates of carbon steel pipelines can be severe. This wear mechanism is known as erosion-corrosion and consists of erosion and corrosion components, with degradation enhanced by interactions between the mechanisms. A lack of understanding of erosion-corrosion of carbon steel and the mechanisms contributing to enhanced degradation through erosion and corrosion interactions exists. Erosion-corrosion of carbon steel in CO2 conditions was the subject of investigation in this work. A submerged impinging jet (SIJ) was used to complete a case study of erosion-corrosion degradation of X65 carbon steel in field conditions at high flow velocities up to 20 m/s in a 60°C, pH 4.7, 2 wt.% NaCl solution containing up to 1000 mg/L of sand particles with an average diameter of 250 μm. High degradation rates, some in excess of 25 mm/yr, were measured and whilst corrosion inhibitors added to protect the X65 surface did reduce corrosion rates, they did not reduce erosion degradation, resulting in degradation rates remaining greater than 10 mm/yr in the most severe conditions evaluated. An investigation into the mechanisms of erosion-corrosion interactions revealed that work-hardened layers were thick and more refined on samples subject to erosion conditions compared with samples used in erosion-corrosion tests. This was explained by removal of the work-hardened layers, formed after particle impacts, through electrochemical dissolution, resulting in corrosion-enhanced erosion, which accounted for up to 20% of overall erosion-corrosion degradation at a flow velocity of 20 m/s in a 60°C, CO2-saturared solution containing 1000 mg/L of sand. Erosion-enhanced corrosion was shown not to be significant in the conditions tested. Flow geometry was also shown to have a significant influence on the erosion-corrosion degradation rates. A 90° elbow was designed to evaluate erosion-corrosion in pipe flow, CO2-saturated, pH 4 conditions at a flow velocity of 6 m/s that showed small erosion contributions to erosion-corrosion degradation on the outer radius of the elbow, with flow induced corrosion accounting for the majority of degradation. To fully understand erosion-corrosion conditions in both flow geometries, computational fluid dynamics (CFD) was used to predict mass transfer coefficients and sand particle trajectories in the flow. Predictions were used to define the erosion mechanisms in the different geometries and to explain why degradation rates could vary significantly between different flow geometries.

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Ebrahim, Alajmi Saad. "Modelling of gas-condensate flow around complex well geometries and cleanup efficiency in heterogeneous systems." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2588.

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Two phase flow of gas and condensate fluids in porous media is different from that of conventional Gas-Oil fluid systems. Such reservoirs are characterized by their complex phase and flow behaviors that significantly affect the well performance. The presence of retrograde fluid, when the pressure drops below dew point, and the dependency of the gas and condensate relative permeability (kr) on the velocity and interfacial tension (IFT) makes numerical modeling and performance prediction of gas condensate systems a real challenge, especially for complex well geometries such as hydraulically fractured wells (HFWs). The current research work is divided into three elements. The first one is devoted to study the flow behaviour around Single and Multi-layer hydraulically fractured wells (HFWs) in gas condensate reservoirs. Here, several in-house simulators have been developed for single-phase and two-phase gas condensate flow. The two phase in-house simulators correctly account for the phase change and the dependency of relative permeability to velocity and interfacial tension, due to inertia (reduction in kr as velocity increases) and coupling (improvement in kr as velocity increases and/or IFT decrease). The integrity of the in-house simulators have been verified by comparing some of their results with those obtained using the fine grid option of the ECLIPSE (E300) commercial reservoir simulator under the same prevailing flow conditions. Benefiting from, the 2 and 3-D in-house simulators a large data bank has been generated covering a wide range of variations of pertinent geometrical and flow parameters. Then, a new formula is proposed for estimation of an effective wellbore radius of an equivalent open-hole (EOH) radial 1-D system replicating flow around the 2 and 3-D HFW systems. The proposed formulation is general, in the sense that if the total gas fractional flow (GTR) is unity, then it correctly converts to that suitable for single phase gas system under Non-Darcy flow conditions and when Reynolds number is small to that under Darcy flow conditions. The second part of this thesis is devoted to study the optimization of hydraulic fracture geometry in gas condensate reservoirs. In this part of the study, a general optimum fracture design formulation is proposed based on the effective proppant number concept. In this new formula the maximum productivity index and optimum penetration ratio can be calculated for a certain proppant number, both accounted for the coupling and inertia effects. Here an effective proppant number formula is proposed (i.e. correcting the absolute proppant number for the effect of coupling and inertia). The proposed formula is general as it correctly converts to that suitable for single-phase Darcy and Non-Darcy flow. Furthermore, using the effective proppant number formula proposed here, the well-known Unified Fracture Design (UFD, Economides and Valko formula) has been modified to account for gas condensate flow conditions, i.e. coupling and inertia effects. The third part of this research work presents a thorough and extensive evaluation of the impact of the pertinent parameters on the clean-up efficiency process, which is often considered as one of the main reasons for the under-performance of hydraulic fracturing treatments, in gas reservoirs. In fact, most available clean up efficiency literature studies are concentrated on evaluating the impact of a single pertinent parameter at a time. That is, none of these studies have investigated the variation of all pertinent parameters simultaneously over a wide practical range of their variations, which may help in better understanding of the clean-up process and may provide practical guidelines to successful hydraulic fracturing jobs. Accordingly, this work embarked on a much more expanded study following statistical approaches. First, the key parameters which have significant impact on the gas production loss (GPL) are identified and then a 2-level full factorial statistical experimental design method has been used to sample a reasonably wide range of variation of pertinent parameters covering many practical cases for a total of 12 parameters. Since over 36,000 simulation runs were required, to cover the range of variation of all parameters, the simulation process has been simplified using a computer code, which was developed to automatically link different stages of these simulations. The analysis of the simulation runs using two response surface models (with and without interaction of parameters) demonstrates the relative importance of the pertinent parameters after different production time periods and provide a practical guidelines to a successful hydraulic fracturing job. In conclusion, this research cover the following main elements of HFW research, 1) – To propose simple numerical modelling methods for gas and gas condensate flow around single and multi-Layer HFWs, 2) – To propose a general Optimum Fracture Design method for gas and gas condensate reservoirs, which correctly account for the effects of coupling and inertia. 3) – To provide a thorough and extensive evaluation of the impact of pertinent parameters on clean-up efficiency of hydraulically fractured gas well.

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38

Boehm, Brian Patrick. "Performance optimization of a subsonic Diffuser-Collector subsystem using interchangeable geometries." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/49589.

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A subsonic wind tunnel facility was designed and built to test and optimize various diffuser-collector box geometries at the one-twelfth scale. The facility was designed to run continuously at an inlet Mach number of 0.42 and an inlet hydraulic diameter Reynolds number of 340,000. Different combinations of diffusers, hubs, and exhaust collector boxes were designed and evaluated for overall optimum performance. Both 3-hole and 5-hole probes were traversed into the flow to generate multiple diffuser inlet and collector exit performance profile plots. Surface oil flow visualization was performed to gain an understanding of the complex 3D flow structures inside the diffuser-collector subsystem. The cutback radial hardware was found to increase the subsystem pressure recovery by over 10% from baseline resulting in an approximate 1% increase in gas turbine power output.
Master of Science

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39

Agartan, Yigit Ata. "Experimental Comparison Of Different Minichannel Geometries For Use In Evaporators." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614095/index.pdf.

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This thesis investigates the refrigerant (R-134a) flow in three minichannels having different geometries experimentally. During the last 40 years heat transfer in small scales has been a very attractive research area. Improvements in heat transfer in the refrigeration applications by means of usage of micro/minichannels provide significant developments in this area. Also it is known that experimental studies are very important to constitute a database which is beneficial for new developments and research. During the two-phase flow experiments conducted in the minichannels, low mass flow rates and constant wall temperature approach, which are the conditions in the evaporators of the refrigerator applications were applied because one of the purposes of this study is to determine the most ideal minichannel among the tested minichannels for usage in the evaporator section of the refrigerators. Two-phase flow experiments were made with refrigerant R134a in the three minichannels having hydraulic diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the third minichannel has a rough inner surface. Comparison of the experimental results of the three minichannels was made in terms of forced convection heat transfer coefficients and pressure drop at constant quality and mass flux values. As a result of the experiments, the most ideal minichannel among the tested minichannels was determined for the evaporator applications in the refrigerators.

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40

Wüthrich, Benjamin. "Simulation and validation of compressible flow in nozzle geometries and validation of OpenFOAM for this application." Zürich : ETH, Swiss Federal Institute of Technology Zurich, Institute of Fluid Dynamics, 2007. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=364.

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41

黃潤棠 and Yun-tong Anton Wong. "Computational study of wind flow and pollution dispersion in an urban street canyon of various geometries." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31226905.

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Wong, Yun-tong Anton. "Computational study of wind flow and pollution dispersion in an urban street canyon of various geometries /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25211754.

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43

Kourakos, Vasilios. "Experimental study and modeling of single- and two-phase flow in singular geometries and safety relief valves." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209827.

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This research project was carried out at the von Karman Institute for Fluid Dynamics (VKI), in Belgium, in collaboration and with the funding of Centre Technique des Industries Mécaniques (CETIM) in France.

The flow of a mixture of two fluids in pipes can be frequently encountered in nuclear, chemical or mechanical engineering, where gas-liquid eactors, boilers, condensers, evaporators and combustion systems can be used. The presence of section changes or more generally geometrical singularities in pipes may affect significantly the behavior of twophase flow and subsequently the resulting pressure drop and mass flow rate. Therefore, it is an important subject of investigation in particular when the application concerns industrial safety valves.

This thesis is intended to provide a thorough research on two-phase (air-water) flow phenomena under various circumstances. The project is split in the following steps. At first, experiments are carried out in simple geometries such as smooth and sudden divergence and convergence singularities. Two experimental facilities are built; one in smaller scale in von Karman Institute and one in larger scale in CETIM. During the first part of the study, relatively simple geometrical discontinuities are investigated. The characterization and modeling of contraction and expansion nozzles (sudden and smooth change of section) is carried out. The pressure evolution is measured and pressure drop correlations are deduced. Flow visualization is also performed with a high-speed camera; the different flow patterns are identified and flow regime maps are established for a specific configuration.

A dual optical probe is used to determine the void fraction, bubble size and velocity upstream and downstream the singularities.

In the second part of the project, a more complex device, i.e. a Safety Relief Valve (SRV), mainly used in nuclear and chemistry industry, is thoroughly studied. A transparent model of a specific type of safety valve (1 1/2" G 3") is built and investigated in terms of pressure evolution. Additionally, flow rate measurements for several volumetric qualities and valve openings are carried out for air, water and two-phase mixtures. Full optical access allowed identification of the structure of the flow. The results are compared with measurements performed at the original industrial valve. Flowforce analysis is performed revealing that compressible and incompressible flowforces in SRV are inversed above a certain value of valve lift. This value varies with critical pressure ratio, therefore is directly linked to the position at which chocked flow occurs during air valve operation. In two-phase flow, for volumetric quality of air=20%, pure compressible flow behavior, in terms of flowforce, is remarked at full lift. Numerical simulations with commercial CFD code are carried out for air and water in axisymmetric 2D model of the valve in order to verify experimental findings.

The subject of modeling the discharge through a throttling device in two-phase flow is an important industrial problem. The proper design and sizing of this apparatus is a crucial issue which would prevent its wrong function or accidental operation failure that could cause a hazardous situation. So far reliability of existing models predicting the pressure drop and flow discharge in two-phase flow through the valve for various flow conditions is questionable. Nowadays, a common practice is widely adopted (standard ISO 4126-10 (2010), API RP 520 (2000)); the Homogeneous Equilibrium Method with the so-called !-method, although it still needs further validation. Additionally, based on !-methodology, Homogeneous Non-Equilibrium model has been proposed by Diener and Schmidt (2004) (HNE-DS), introducing a boiling delay coefficient. The accuracy of the aforementioned models is checked against experimental data both for transparent model and industrial SRV. The HNE-DS methodology is proved to be the most precise among the others. Finally, after application of HNE-DS method for air-water flow with cavitation, it is concluded that the behavior of flashing liquid is simulated in such case. Hence, for the specific tested conditions, this type of flow can be modeled with modified method of Diener and Schmidt (CF-HNE-DS) although further validation of this observation is required.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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44

Dobes, Jiri. "Numerical algorithms for the computation of steady and unsteady compressible flow over moving geometries: application to fluid-structure interaction." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210640.

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This work deals with the development of numerical methods for compressible flow simulation with application to the interaction of fluid flows and structural bodies.

First, we develop numerical methods based on multidimensional upwind residual distribution (RD) schemes. Theoretical results for the stability and accuracy of the methods are given. Then, the RD schemes for unsteady problems are extended for computations on moving meshes. As a second approach, cell centered and vertex centered finite volume (FV) schemes are considered. The RD schemes are compared to FV schemes by means of the 1D modified equation and by the comparison of the numerical results for scalar problems and system of Euler equations. We present a number of two and three dimensional steady and unsteady test cases, illustrating properties of the numerical methods. The results are compared with the theoretical solution and experimental data.

In the second part, a numerical method for fluid-structure interaction problems is developed. The problem is divided into three distinct sub-problems: Computational Fluid Dynamics, Computational Solid Mechanics and the problem of fluid mesh movement. The problem of Computational Solid Mechanics is formulated as a system of partial differential equations for an anisotropic elastic continuum and solved by the finite element method. The mesh movement is determined using the pseudo-elastic continuum approach and solved again by the finite element method. The coupling of the problems is achieved by a simple sub-iterative approach. Capabilities of the methods are demonstrated on computations of 2D supersonic panel flutter and 3D transonic flutter of the AGARD 445.6 wing. In the first case, the results are compared with the theoretical solution and the numerical computations given in the references. In the second case the comparison with experimental data is presented.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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45

Nicolaou, Fernandez Laura. "A robust immersed boundary method for flow in complex geometries : study of aerosol deposition in the human extrathoracic airways." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9288.

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The flow and the transport of particles in the human respiratory system dictate the effectiveness of therapeutic aerosols used in inhaled drug delivery. The aerosol particles are generally inhaled through the mouth, passing by the throat before reaching the targeted areas in the lungs. Therefore, knowledge of the particle deposition in the mouth-throat region is critical in the design of effective inhalation devices for optimum delivery to the lungs. Numerical simulations offer a non-invasive and cost-effective alternative to in vivo and in vitro tests. However, accurate prediction remains a challenge for numerical models due to the complexity of the flow in the extrathoracic airways. A robust immersed boundary method for flow in complex geometries is proposed. This greatly simplifies the task of grid generation and eliminates the problems associated with grid quality that exist for boundary-fitted grid techniques. The proposed method is an extension to the momentum forcing approach onto curvilinear coordinates and applies an iterative procedure to compute the forcing term implicitly, which stabilizes the scheme for higher Reynolds numbers. The use of a curvilinear grid minimizes the number of unused cells outside the geometry and increases the efficiency of the numerical scheme. The method is validated against numerical and experimental data in the literature for a number of test cases on both Cartesian and curvilinear grids. The results show good agreement with previous studies. Direct numerical simulations were performed in a number of realistic mouth and throat geometries obtained from MRI scans. A Lagrangian particle tracking scheme was employed to advance the particles dynamically, and total and regional deposition efficiencies were determined and compared to in vitro data. The effect of inflow turbulence and intersubject variation on deposition was studied. Geometric variation has a large impact on total deposition whereas the effect of inflow turbulence is confined to oral deposition.

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Chen, Ching-Hsien. "Tools for developing continuous-flow micro-mixer : numerical simulation of transitional flow in micro geometries and a quantitative technique for extracting dynamic information from micro-bubble images." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/57599/.

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Recent advance in the microfluidics including its fabrication technologies has led to many novel applications in micro-scale flows. Among them is the continuous-flow micromixer that utilizes the advantages associated with turbulent flows for rapid mixing, achieving the detection of fast kinetic reaction as short as tens of microseconds. However, for developing a high performance continuous-flow micromixer there are certain fundamental issues need to be solved. One of them is an universal simulation approach capable of calculating the flow field across entire passage for entire regime from very low Reynolds number laminar flow through transition to fully turbulent flow. Though the direct numerical simulation is potentially possible solution but its extremely high computing time stops itself from practical applications. The second major issue is the inevitable occurrence of cavitation bubbles in this rapid flow apparatus. This phenomenon has opposite effects: (a) deteriorating performance and damaging the micromixer; (b) playing a catalyst role in enhancing mixing. A fully understanding of these micro bubbles will provide a sound theoretical base for guiding the design of micromixer in order to explore the advantage to maximum while minimizing its disadvantages. Therefore, the objectives of this PhD programme is to study the tools that will effectively advance our fundamental understandings on these key issues while in short term fulfil the requires from the joint experimental PhD programme held in the life science faculty for designing a prototype experimental device. During this PhD study, an existing numerical approach suitable for predicting the possibly entire flow regime including the turbulence transition is proposed for simulating the microscale flows in the microchannel and micromixer. The simulation results are validated against the transitional micro-channel experiments and this numerical method is then further applied for the micromixer simulation. This provides the researcher a realistic and feasible CFD tool to establish guidelines for designing high-efficiency and cost-effective micromixers by utilizing various possible measures which may cause very different flows simultaneously in micromixer. In order to study microscale cavitation bubbles and their effects on micromixers, an innovative experimental setup is purposely designed and constructed that can generate laser-induced micro-bubbles at desired position and size for testing. Experiments withvarious micro-scale bubbles have been performed successfully by using an ultra high-speed camera up to 1 million frame rate per second. A novel technique for tracking the contours of micro-scale cavitation bubble dynamically has been developed by using active contour method. By using this technique, for the first time, various geometric and dynamic data of cavitation bubble have been obtained to quantitatively analyze the global behaviours of bubbles thoroughly. This powerful tool will greatly benefit the study of bubble dynamics and similar demands in other fields for fast and accurate image treatments as well.

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47

Adams, Aaron J. "Relationships between observed pore and pore-throat geometries, measured porosity and permeability, and indirect measures of pore volume by nuclear magnetic resonance." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4710.

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Carbonate reservoirs are a network of pores and connecting pore-throats that contain at least half of the world's oil. Genetic classification of carbonate pores enables one to map the pore types that have greatest influence on reservoir performance. Though NMR logging has been used to estimate pore sizes, it has not been used to identify genetic pore types or to aid in determinations of reservoir quality for different pore assemblages. Five genetic pore types identified in 40 carbonate and 7 sandstone samples were subjected to NMR measurements. Results reveal close correspondence between NMRderived pore volumes and 2-D pore size and shape gleaned from petrographic image analysis. Comparisons of real and synthetic pore shapes showed that shapes of all pore types in the medium size range of 0.02-0.5mm can be reliably compared with synthetic varieties, but such comparisons were unreliable for vuggy pores smaller than 0.5mm. T2 relaxation times for depositional pores exhibit low amplitude, narrow wavelength responses. Moldic pores produced medium amplitude, asymmetrical wavelength responses, and intercrystalline pores show high amplitude, narrow wavelength responses. NMR-derived pore volumes on pores with ferroan dolomite interiors underestimated pore diameter by up to 3 orders of magnitude. Calculated pore-throat sizes from MICP data correlate strongly with measured permeability. Samples with high, intermediate, or low poroperm values displayed characteristic T2 curves confirming that reservoir quality can be estimated from NMR measurements. Future work is expected to show that NMR logging can estimate reservoir quality at field scale and aid in mapping flow units in compartmentalized reservoirs.

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48

Heinrich, Christoph [Verfasser]. "A Finite Volume Method on NURBS Geometries and its Application in Fluid Flow and Isogeometric Fluid-Structure Interaction / Christoph Heinrich." München : Verlag Dr. Hut, 2012. http://d-nb.info/1023435136/34.

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Isler, João Anderson. "Computational study in fluid mechanics of bio-inspired geometries: constricted channel and paediatric ventricular assist device." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3150/tde-18072018-140712/.

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Numerical modelling and simulation are powerful tools for analysis and design, and with the improvement of computational power and numerical methods they are being applied on complex phenomena and systems. This work shows examples of the application of a very sophisticated numerical method, namely the Spectral/hp element method, in the study of the flow inside bioinspired complex geometries. The two topics investigated are fluid dynamic instabilities in a constricted channel and flow inside a paediatric ventricular assist device were studied by means of computational fluid mechanics. The constricted channel is an idealized model of a nasal cavity, which is characterized by complex airway channels, and also bears some resemblance to a human artery in the presence of an atherosclerotic plaques. The paediatric ventricular assist device is an actual device, designed by the Bioengineering research group of the Heart Institute of the Medicine School of the University of São Paulo, which works as a pump that assists the left ventricle of patients waiting for transplantation. Therefore, the aim of this thesis is to contribute in the understanding of biological and bio-inspired geometries flows, using computational tools. Linear and nonlinear stability were carried out for the constricted channel. Three different flow regimes were investigated: symmetric steady flow, which is stable for low Reynolds number, asymmetric steady flow, which rises as a result of the primary bifurcation of the symmetric flow and pulsatile flow. Direct stability analysis was carried out to determine the unstable regions and the critical values for each flow regime. The physical mechanisms behind the transition processes were studied by means of direct numerical simulations to characterize the bifurcations. Since the bifurcations had subcritical behaviour, the relevance of non-normal growth in these flows was assessed. Dependence on phase, Reynolds number and spanwise wavenumber of optimal modes were extensively investigated in stable regions of the three flow regimes. Convective instabilities were also studied in order to comprehend the physical mechanisms which led the optimal modes to their maxima growth, and different convective mechanisms were found. The flow inside the paediatric ventricular assist device was analyzed by means of threedimensional numerical simulations. A computational model based on special boundaries conditions was developed to model the pulsatile flow. In this model, the opening and closure of the mitral valve and diaphragm were represented with the use of specially devised boundary conditions. The driving force and the flow direction of the diaphragm were defined by velocity distribution on the diaphragm wall, and the opening and closure of the mitral valve were performed by a velocity waveform which goes to zero in the systolic period. Flow patterns, velocity fields and time-average wall shear rate were analyzed to evaluate the performance of the device.
Modelagem e simulação numéricas são ferramentas poderosas para análise e design, e com a melhoria do poder computacional e dos métodos numéricos, eles estão sendo aplicados em fenômenos e sistemas complexos. Este trabalho mostra exemplos de aplicações de um método numérico sofisticado, o método dos elementos espectrais/hp, no estudo do escoamento dentro de geometrias complexas bio-inspiradas. Os dois tópicos investigados são: instabilidades em dinâmica de fluido em um canal constrito e o escoamento dentro de um dispositivo de assistência ventricular pediátrica. O canal constrito é um modelo idealizado de uma cavidade nasal, que é caracterizada por canais complexos da via aérea, e também tem semelhança com uma artéria humana na presença de placas ateroscleróticas. O dispositivo de assistência ventricular pediátrica é um dispositivo real, projetado pelo grupo de pesquisa de Bioengenharia do Instituto do Coração da Faculdade de Medicina da Universidade de São Paulo, que funciona como uma bomba que auxilia o ventrículo esquerdo dos pacientes à espera de transplante. Portanto, o objetivo desta tese é contribuir na compreensão de escoamentos em geometrias biológicas e bio-inspiradas, usando ferramentas computacionais. Análises de estabilidade linear e não linear foram feitas para um canal constrito. Três diferentes regimes de escoamento foram empregados: escoamento estacionário simétrico, que é estável para baixo número de Reynolds, escoamento assimétrico, o qual é resultado da primeira bifurcação do escoamento simétrico e escoamento pulsátil. Análise de estabilidade direta foi executada para determinar as regiões instáveis em cada regime de escoamento. Os mecanismos físicos por trás do processo de transição foram estudados por meio de simulação numérica direta para caracterizar as bifurcações. Uma vez que, as bifurcações tiveram um comportamento subcrítico, a relevância do crescimento não normal nestes escoamentos foi avaliado. Assim, dependência com a fase, número de Reynolds e número de onda do modo tridimensional foram extensivamente investigados em regiões estáveis para os três regimes de escoamento. Instabilidades convectivas foram também estudadas a fim de compreender os mecanismos físicos que conduzem os modos ótimos para seus crescimentos máximos, e diferentes mecanismos convectivos foram encontrados. O escoamento dentro do dispositivo de assistência ventricular pediátrico foi analisado por meios de simulações numéricas tridimensionais. Um modelo computacional baseado em condições de contorno especiais foi desenvolvido para modelar o escoamento pulsátil. Neste modelo, a abertura e fechamento da válvula mitral e diafragma foram representados com o uso de condições de contorno especialmente elaboradas. A força motora e o direcionamento do fluxo do diafragma foram definidos por uma distribuição de velocidades na parede do diafragma, e a abertura e fechamento da válvula mitral foram executadas por uma função de onda de velocidade que vai a zero no período sistólico. Padrões do escoamento, campos de velocidade e tensão de cisalhamento no tempo foram analisadas para avaliar o desempenho do dispositivo.

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Andrew, Chryss, and andrew chryss@rmit edu au. "Pipeline Transport of Coarse Mineral Suspensions Displaying Shear Thickening." RMIT University. Civil, Environmental and Chemical Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20081127.112225.

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Transport properties of concentrated suspensions are of interest to many industries. Mineral slurries at higher solids concentrations have shown some rheologically interesting characteristics such as shear thickening, the increase of viscosity of a multi-phase mixture with increasing shear rate. The general literature on the rheology of suspensions records the presence of yield stresses, shear thinning and normal stress differences. Little is said specifically about shear thickening behaviour except for colloidal suspensions. The aim of this study is to examine the behaviour of coarse shear thickening suspensions and determine the causes of this phenomenon. The study intended to achieve the following objectives to; develop the appropriate techniques for rheometric studies of shear thickening suspensions; investigate the nature of particle-fluid interaction; develop a model of shear thickening behaviour as it occurs in non-colloidal suspensions and to develop a method of applying the rheology results to flows and flow geometries of practical relevance. The effects of wall slip dominate much of the literature of shear thickening materials. To investigate this aspect a significant portion of the experimental work examined the effect of shear thickening on torsional flow. The rheogram produced from parallel plate rheometry was reassessed as a non-controlled flow and a rheology model dependant analysis demonstrated that the effects of slip are considerably more problematic for shear thickening suspensions, particularly as wall slip is an increasing function of shear stress. As a consequence of the rheometric method described above it was observed that the rate of change of the first normal stress difference, N1, with shear rate changes as shear thickening commences for non-colloidal suspensions. N1 is initially negative and is increasingly negative at low shear rates. Additional rheometric analysis examined the transient effects in the behaviour of a non-colloidal shear thickening suspension. By employing large angle oscillating strain tests the strain required to initiate a shear thickening response was determined. Coherent back scattering of laser light experiments were able to show the change in orientation of the particles with respect to its rotation around the vorticity axis. After a viscosity minimum was reached the orientation became more random as particle rotation and lamina disruption occurred. This was considered to be the cause of the measured shear thickening. A model of shear thickening in concentrated, non-colloidal suspensions of non-spherical particles was developed. Based on hydrodynamic interaction in the Stokes flow regime, the flow of interstitial fluid subjected the adjacent particles to lubricating and Couette type forces, acting as a couple. When a series of force balances on a particle contained between two moving laminae are conducted as a time sequence, the particle orientation and motion can be observed. The model has qualitative agreement with several aspects of the experimentally observed behaviour of shear thickening suspensions, such as viscosity change with shear rate and concentration, and the first normal stress difference increasing with shear rate. Pipe line flow experiments were conducted on the model suspension. Particle settling produces unusual patterns in shear thickening suspensions, with an annulus of delayed settling near the wall.

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Dissertations / Theses on the topic 'Flow geometries'

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