Dissertations / Theses on the topic 'Experimental methods in fluid flow'

Turbulent mixing is present in many pulp and paper processes. It is a particularly important factor in the design and improvements of the paper machine headbox, influencing the final paper structure. During this project, experimental methods to quantify the effect of fibers on turbulent suspension flows have been developed, and then used for studying turbulent mixing in fiber suspensions. A technique that uses microprobes to measure passive scalar mixing of salt for the characterization of turbulent fluctuations in a fiber suspension flow has been developed: Conductivity micro-probes have been built and turbulence measurements have been performed in simple jet and wake flows, studying turbulent mixing between the two streams of pulp suspension, of which one has been doped with salt. A relatively new technique to measure fluid velocity non-intrusively in opaque fluids has also been tested. The technique makes use of ultrasonic pulses to obtain velocity information through the Doppler-shift of reflected pulses. The main efforts reported on in the thesis are focused on method design and development as well as method evaluation.

The study and modelling of two-phase flow, even the simplest ones such as the bubbly flow, remains a challenge that requires exploring the physical phenomena from different spatial and temporal resolution levels. CFD (Computational Fluid Dynamics) is a widespread and promising tool for modelling, but nowadays, there is no single approach or method to predict the dynamics of these systems at the different resolution levels providing enough precision of the results. The inherent difficulties of the events occurring in this flow, mainly those related with the interface between phases, makes that low or intermediate resolution level approaches as system codes (RELAP, TRACE, ...) or 3D TFM (Two-Fluid Model) have significant issues to reproduce acceptable results, unless well-known scenarios and global values are considered. Instead, methods based on high resolution level such as Interfacial Tracking Method (ITM) or Volume Of Fluid (VOF) require a high computational effort that makes unfeasible its use in complex systems. In this thesis, an open-source simulation framework has been designed and developed using the OpenFOAM library to analyze the cases from microescale to macroscale levels. The different approaches and the information that is required in each one of them have been studied for bubbly flow. In the first part, the dynamics of single bubbles at a high resolution level have been examined through VOF. This technique has allowed to obtain accurate results related to the bubble formation, terminal velocity, path, wake and instabilities produced by the wake. However, this approach has been impractical for real scenarios with more than dozens of bubbles. Alternatively, this thesis proposes a CFD Discrete Element Method (CFD-DEM) technique, where each bubble is represented discretely. A novel solver for bubbly flow has been developed in this thesis. This includes a large number of improvements necessary to reproduce the bubble-bubble and bubble-wall interactions, turbulence, velocity seen by the bubbles, momentum and mass exchange term over the cells or bubble expansion, among others. But also new implementations as an algorithm to seed the bubbles in the system have been incorporated. As a result, this new solver gives more accurate results as the provided up to date. Following the decrease on resolution level, and therefore the required computational resources, a 3D TFM have been developed with a population balance equation solved with an implementation of the Quadrature Method Of Moments (QMOM). The solver is implemented with the same closure models as the CFD-DEM to analyze the effects involved with the lost of information due to the averaging of the instantaneous Navier-Stokes equation. The analysis of the results with CFD-DEM reveals the discrepancies found by considering averaged values and homogeneous flow in the models of the classical TFM formulation. Finally, for the lowest resolution level approach, the system code RELAP5/MOD3 is used for modelling the bubbly flow regime. The code has been modified to reproduce properly the two-phase flow characteristics in vertical pipes, comparing the performance of the calculation of the drag term based on drift-velocity and drag coefficient approaches.
El estudio y modelado de flujos bifásicos, incluso los más simples como el bubbly flow, sigue siendo un reto que conlleva aproximarse a los fenómenos físicos que lo rigen desde diferentes niveles de resolución espacial y temporal. El uso de códigos CFD (Computational Fluid Dynamics) como herramienta de modelado está muy extendida y resulta prometedora, pero hoy por hoy, no existe una única aproximación o técnica de resolución que permita predecir la dinámica de estos sistemas en los diferentes niveles de resolución, y que ofrezca suficiente precisión en sus resultados. La dificultad intrínseca de los fenómenos que allí ocurren, sobre todo los ligados a la interfase entre ambas fases, hace que los códigos de bajo o medio nivel de resolución, como pueden ser los códigos de sistema (RELAP, TRACE, etc.) o los basados en aproximaciones 3D TFM (Two-Fluid Model) tengan serios problemas para ofrecer resultados aceptables, a no ser que se trate de escenarios muy conocidos y se busquen resultados globales. En cambio, códigos basados en alto nivel de resolución, como los que utilizan VOF (Volume Of Fluid), requirieren de un esfuerzo computacional tan elevado que no pueden ser aplicados a sistemas complejos. En esta tesis, mediante el uso de la librería OpenFOAM se ha creado un marco de simulación de código abierto para analizar los escenarios desde niveles de resolución de microescala a macroescala, analizando las diferentes aproximaciones, así como la información que es necesaria aportar en cada una de ellas, para el estudio del régimen de bubbly flow. En la primera parte se estudia la dinámica de burbujas individuales a un alto nivel de resolución mediante el uso del método VOF (Volume Of Fluid). Esta técnica ha permitido obtener resultados precisos como la formación de la burbuja, velocidad terminal, camino recorrido, estela producida por la burbuja e inestabilidades que produce en su camino. Pero esta aproximación resulta inviable para entornos reales con la participación de más de unas pocas decenas de burbujas. Como alternativa, se propone el uso de técnicas CFD-DEM (Discrete Element Methods) en la que se representa a las burbujas como partículas discretas. En esta tesis se ha desarrollado un nuevo solver para bubbly flow en el que se han añadido un gran número de nuevos modelos, como los necesarios para contemplar los choques entre burbujas o con las paredes, la turbulencia, la velocidad vista por las burbujas, la distribución del intercambio de momento y masas con el fluido en las diferentes celdas por cada una de las burbujas o la expansión de la fase gaseosa entre otros. Pero también se han tenido que incluir nuevos algoritmos como el necesario para inyectar de forma adecuada la fase gaseosa en el sistema. Este nuevo solver ofrece resultados con un nivel de resolución superior a los desarrollados hasta la fecha. Siguiendo con la reducción del nivel de resolución, y por tanto los recursos computacionales necesarios, se efectúa el desarrollo de un solver tridimensional de TFM en el que se ha implementado el método QMOM (Quadrature Method Of Moments) para resolver la ecuación de balance poblacional. El solver se desarrolla con los mismos modelos de cierre que el CFD-DEM para analizar los efectos relacionados con la pérdida de información debido al promediado de las ecuaciones instantáneas de Navier-Stokes. El análisis de resultados de CFD-DEM permite determinar las discrepancias encontradas por considerar los valores promediados y el flujo homogéneo de los modelos clásicos de TFM. Por último, como aproximación de nivel de resolución más bajo, se investiga el uso uso de códigos de sistema, utilizando el código RELAP5/MOD3 para analizar el modelado del flujo en condiciones de bubbly flow. El código es modificado para reproducir correctamente el flujo bifásico en tuberías verticales, comparando el comportamiento de aproximaciones para el cálculo del término d
L'estudi i modelatge de fluxos bifàsics, fins i tot els més simples com bubbly flow, segueix sent un repte que comporta aproximar-se als fenòmens físics que ho regeixen des de diferents nivells de resolució espacial i temporal. L'ús de codis CFD (Computational Fluid Dynamics) com a eina de modelatge està molt estesa i resulta prometedora, però ara per ara, no existeix una única aproximació o tècnica de resolució que permeta predir la dinàmica d'aquests sistemes en els diferents nivells de resolució, i que oferisca suficient precisió en els seus resultats. Les dificultat intrínseques dels fenòmens que allí ocorren, sobre tots els lligats a la interfase entre les dues fases, fa que els codis de baix o mig nivell de resolució, com poden ser els codis de sistema (RELAP,TRACE, etc.) o els basats en aproximacions 3D TFM (Two-Fluid Model) tinguen seriosos problemes per a oferir resultats acceptables , llevat que es tracte d'escenaris molt coneguts i se persegueixen resultats globals. En canvi, codis basats en alt nivell de resolució, com els que utilitzen VOF (Volume Of Fluid), requereixen d'un esforç computacional tan elevat que no poden ser aplicats a sistemes complexos. En aquesta tesi, mitjançant l'ús de la llibreria OpenFOAM s'ha creat un marc de simulació de codi obert per a analitzar els escenaris des de nivells de resolució de microescala a macroescala, analitzant les diferents aproximacions, així com la informació que és necessària aportar en cadascuna d'elles, per a l'estudi del règim de bubbly flow. En la primera part s'estudia la dinàmica de bambolles individuals a un alt nivell de resolució mitjançant l'ús del mètode VOF. Aquesta tècnica ha permès obtenir resultats precisos com la formació de la bambolla, velocitat terminal, camí recorregut, estela produida per la bambolla i inestabilitats que produeix en el seu camí. Però aquesta aproximació resulta inviable per a entorns reals amb la participació de més d'unes poques desenes de bambolles. Com a alternativa en aqueix cas es proposa l'ús de tècniques CFD-DEM (Discrete Element Methods) en la qual es representa a les bambolles com a partícules discretes. En aquesta tesi s'ha desenvolupat un nou solver per a bubbly flow en el qual s'han afegit un gran nombre de nous models, com els necessaris per a contemplar els xocs entre bambolles o amb les parets, la turbulència, la velocitat vista per les bambolles, la distribució de l'intercanvi de moment i masses amb el fluid en les diferents cel·les per cadascuna de les bambolles o els models d'expansió de la fase gasosa entre uns altres. Però també s'ha hagut d'incloure nous algoritmes com el necessari per a injectar de forma adequada la fase gasosa en el sistema. Aquest nou solver ofereix resultats amb un nivell de resolució superior als desenvolupat fins la data. Seguint amb la reducció del nivell de resolució, i per tant els recursos computacionals necessaris, s'efectua el desenvolupament d'un solver tridimensional de TFM en el qual s'ha implementat el mètode QMOM (Quadrature Method Of Moments) per a resoldre l'equació de balanç poblacional. El solver es desenvolupa amb els mateixos models de tancament que el CFD-DEM per a analitzar els efectes relacionats amb la pèrdua d'informació a causa del promitjat de les equacions instantànies de Navier-Stokes. L'anàlisi de resultats de CFD-DEM permet determinar les discrepàncies ocasionades per considerar els valors promitjats i el flux homogeni dels models clàssics de TFM. Finalment, com a aproximació de nivell de resolució més baix, s'analitza l'ús de codis de sistema, utilitzant el codi RELAP5/MOD3 per a analitzar el modelatge del fluxos en règim de bubbly flow. El codi és modificat per a reproduir correctament les característiques del flux bifàsic en canonades verticals, comparant el comportament d'aproximacions per al càlcul del terme de drag basades en velocitat de drift flux model i de les basades en coe
Peña Monferrer, C. (2017). Computational fluid dynamics multiscale modelling of bubbly flow. A critical study and new developments on volume of fluid, discrete element and two-fluid methods [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90493
TESIS

In a proposed design for a concentrated solar power tower, sand is irradiated by solar energy and transfers its energy to another fluid stream by means of a finned tube heat exchanger. To maximize heat transfer and minimize potential damage to the heat exchanger, it is desired to have a very uniform flow through the heat exchanger. However, performing full scale flow tests can be expensive, impractical, and depending upon the specific quantities of interest, unsuitable for revealing the details of what it happening inside of the flow stream. Thus, the discrete element method has been used to simulate and study particulate flows. In this project, the flow of small glass beads through a square pyramid shaped hopper and a wedge shaped hopper were studied at the lab scale. These flows were also simulated using computers running two versions of discrete element modeling software – EDEM and LIGGGHTS. The simulated results were compared against the lab scale flows and against each other. They show that, in general, the discrete element method can be used to simulate lab scale particulate flows as long as certain material properties are well known, especially the friction properties of the material. The potential for increasing the accuracy of the simulations, such as using better material property data, non-uniform particle size distributions, and non-spherical particle shapes, as well as simulating heat transfer within a granular flow are also discussed.

Transportation of unprocessed multiphase reservoir fluids from deep/ultra deep offshore through a long subsea tieback/pipeline is inevitable. This form of transportation is complex and requires accurate knowledge of critical transport velocity, flow pattern changes, phase velocity, pressure drop, particle drag & lift forces, sand/liquid/gas holdup, flow rate requirement and tieback sizing etc at the early design phase and during operation for process optimisation. This research investigated sand transport characteristics in multiphase, water‐oil‐gas‐sand flows in horizontal, inclined and vertical pipes. Two critical factors that influence the solid particle transport in the case of multiphase flow in pipes were identified; these are the transient phenomena of flow patterns and the characteristic drag & lift coefficients ( D C , L C ). Therefore, the equations for velocity profile were developed for key flow patterns such as dispersed bubble flow, stratified flow, slug flow and annular flow using a combination of analytical equations and numerical simulation tool (CFD). The existing correlations for D C & L C were modified with data acquired from multiphase experiment in order to account for different flow patterns. Minimum Transport Velocity (MTV) models for suspension and rolling were developed by combining the numerically developed particle velocity profile models with semi‐empirical models for solid particle transport. The models took into account the critical parameters that influence particle transport in pipe flow such as flow patterns and particle drag & lift coefficients, thus eliminate inaccuracies currently experienced with similar models in public domain. The predictions of the proposed MTV models for suspension and rolling in dispersed bubble, slug flow and annular flow show maximum average error margin of 12% when compared with experimental data. The improved models were validated using previously reported experimental data and were shown to have better predictions when compared with existing models in public domain. These models have the potential to solve the problems of pipe and equipment sizing, the risk of sand deposition and bed formation, elimination of costs of sand unloading, downtime and generally improve sand management strategies.

Les méthodes expérimentales utilisées actuellement pour déterminer la distribution de taille des pores (DTP) dans les milieux poreux présentent des inconvénients, tels que par exemple, la toxicité des fluides employés (porosimétrie à mercure). La base théoriques d'une nouvelle méthode pour obtenir la DTP a été proposée dans la littérature. Celle-ci est fondée sur l'injection de fluides à seuil, caractérisés par une contrainte de cisaillement en deçà de laquelle ils ne s'écoulent pas. L'idée principale de ces travaux théoriques est que l'écoulement de fluides à seuil à travers un milieu poreux permet d'obtenir sa DTP à partir de la mesure des débits correspondant à différents gradients de pression Q(∇P). L'objectif du travail proposé ici est de présenter une nouvelle méthode d'exploitation des données expérimentales Q(∇P) permettant d'obtenir de façon simple, robuste et reproductible les DTPs des milieux poreux analysés. La démarche consiste à évaluer la contribution au débit total des nouveaux pores qui s'incorporent à l'écoulement entre deux valeurs de ∇P. Ces nouveaux pores sont caractérisés par un rayon représentatif qui est fonction de la contrainte seuil du fluide et de ∇P. L'importance de leur contribution au débit total par rapport à celle d'un seul pore donne le nombre de pores dans l'échantillon ayant ce rayon représentatif. Cette méthode est d'abord testée et validée avec des expériences générées numériquement. Ensuite, elle est utilisée pour exploiter des données provenant d'expériences de laboratoire réalisées avec de différents milieux poreux. Les résultats obtenus en termes de DTPs sont comparés avec ceux fournis par d'autres techniques: porosimétrie à mercure et microtomographie
Current experimental methods used to determine pore size distributions (PSD)of porous media present several drawbacks such as toxicity of the employed fluids (e.g., mercury porosimetry). The theoretical basis of a new method to obtain the PSD by injecting yield stress fluids through porous media and measuring the flow rate Q at several pressure gradients ∇P was proposed in the literature. On the basis of these theoretical considerations,an intuitive approach to obtain PSD from Q(∇P) is presented in this work. It relies on considering the extra increment of Q when ∇P is increased, as a consequence of the pores of smaller radius newly incorporated to the flow. This procedure is first tested and validated on numerically generated experiments. Then, it is applied to exploit data coming from laboratory experiments and the obtained PSDs are compared to those deduced by mercury porosimetry and micro tomography

CAPES; PETROBRAS
O escoamento de gás-líquido descendente, no padrão golfadas é frequentemente encontrado em linhas de produção de petróleo provocado pela topografia do terreno. Assim, é necessário entender a dinâmica deste tipo de escoamento para o projeto de linhas de produção de óleo e gás, assim como para o dimensionamento de separadores e equipamentos. Neste cenário, no presente trabalho é caraterizado experimentalmente o escoamento bifásico de líquido-gás no padrão intermitente na direção descendente, em tubulações com inclinações de 0°, −4°, −7°, −10° e −13°. O estudo foi realizado utilizando o circuito experimental instalado no NUEM/UTFPR. Os experimentos foram conduzidos para diferentes condições de vazão de líquido e gás que garantam o padrão intermitente em golfadas, e para a monitoração das estruturas (fases) do escoamento foi utilizado um par de sensores de malha de eletrodos. A partir dos sinais temporais da fração de vazio adquiridos, foram extraídas as distribuições estatísticas dos parâmetros característicos do escoamento em golfadas, sendo estes: a velocidade de translação da bolha alongada, a frequência de passagem da célula unitária, o comprimento do pistão de líquido, o comprimento da bolha alongada e a fração de vazio na região da bolha alongada. Em posse dos dados experimentais processados, estes foram analisados com a finalidade de identificar a relação entre os parâmetros do escoamento em golfadas, tanto para suas distribuições estatísticas como para seu valor médio, com as vazões e propriedade dos fluidos. Foram elaboradas correlações, com intervalo de confiança de 95%, para calcular a frequência, velocidade da bolha alongada, comprimentos do pistão e da bolha, fração do líquido e de vazio; que certamente servirão de referência para o desenvolvimento de modelos matemáticos e desenvolvimento de projetos de engenharia.
Downward slug flow in ducts of circular cross section is a frequently observed flow regime in oil and gas transportation lines. The onset of this kind of flow is due to instabilities generated by irregular pipe topography. Therefore, to understand the hydrodynamics of the slug flow is paramount in the design of crude oil production lines as well as in the project of equipment involved in oil and gas operations. The goal of this work is to experimentally analyze and characterize the two-phase gas-liquid intermittent downward flow in ducts with inclination angles of 0°, −4°, −7°, −10° and −13°. The analysis was performed at different gas-liquid volumetric flow rates for which the slug flow regime was observed. An existing experimental rig in the NUEM/UTFPR labs was used to collect data. A pair of wire-mesh sensors to evaluate the flow structure, thus obtaining void fraction temporal series was employed. From those series, statistical distributions for the characteristic parameters of such slug flows – namely the elongated bubble translational velocity, the unit cell frequency, the liquid slug and the elongated bubble lengths and the void fraction in the elongated bubble region – were obtained. The processed signals were analyzed so as to identify the relationship between the slug flow parameters, their statistical distributions and averaged values alike as functions of the flow rates and fluid properties. Correlations for slug frequency, elongated bubble velocity, liquid slug and bubble lengths as well as empirical expressions for the void and liquid fractions were developed, all within a confidence interval of 95%. It is expected that such correlations may contribute to the betterment of future engineering endeavours, and used in the development of similar mathematical models.

Presentation de la methode fet (formalisme d'evolution par transfert) permettant d'utiliser dans une meme simulation des modeles varies pour les diverses parties du systeme etudie, et d'autre part, de comparer a l'experience sur modele d'ecoulement pour le coeur d'une piece d'habitation succeptible d'etre raccordee a d'autres modeles par le fet. Analyse quantitative des resultats

Etude du decollement de l'ecoulement et de la formation de cellules. Structure et caracteristiques geometriques de ces cellules. Analyse du champ hydrodynamique. Calcul numerique base sur l'ecriture des conditions des conditions aux limites par la methode des moindres carres. Mise au point d'une technique de visualisation par intermittence pendant de longues durees, utilisant les traceurs solides

Le present travail est consacre au developpement et a la validation experimentale d'une methode de prediction quantitative de l'erosion par cavitation. La demarche de prediction retenue consiste a mesurer le potentiel erosif, ou agressivite, d'un ecoulement cavitant afin de le reproduire de facon acceleree puis d'obtenir une mesure previsionnelle de l'erosion. La definition de l'agressivite repose sur l'analyse statistique des microdeformations plastiques isolees formees a la surface des parois solides elastoplastiques au debut de l'endommagement. Les distributions aleatoires, spatiale et dimensionnelle, de ces indentations sont reduites aux trois grandeurs scalaires: vst le volume total des indentations par unite de surface et par unite de temps, rm et hm la moyenne des distributions, ponderees par le volume, du rayon et de la profondeur des indentations. Quant a l'erosion, elle est mesuree par l'evolution de la profondeur de l'endommagement macroscopique des parois au cours du temps. Des mesures d'agressivite et d'erosion ont ete realisees pour des ecoulements venturis experimentaux de deux echelles geometriques differentes. Pour les conditions de similitude caracterisant ces ecoulements cavitants, les transpositions des mesures d'agressivite et d'erosion, associees a un changement d'echelle geometrique et/ou a un changement de vitesse de l'ecoulement, ont ete verifiees. Par ailleurs, il est montre qu'un parametre adimensionnel, ii, caracteristique de l'interaction liquide/solide permet de transposer les mesures de l'agressivite lors d'un changement de materiau, elastoplastique, de la paroi solide de l'ecoulement. L'observation d'une tres forte correlation entre le taux de deformation volumique vst et la vitesse d'erosion permet d'envisager une nouvelle demarche de prediction de l'erosion. Des mesures d'agressivite et d'erosion ont egalement ete realisees pour les ecoulements du caversim, moyen d'essais defini pour la reproduction acceleree de l'endommagement par cavitation. L'observation de la meme correlation entre la mesure de l'agressivite, vst, et la vitesse d'erosion, pour ces ecoulements cavitants tout a fait differents des ecoulements venturis, permet de valider experimentalement la methode proposee de prediction de l'erosion par cavitation

Etude d'un amortisseur hydraulique de suspension automobile. Calcul de l'amortissement et des pertes de charge. Influence du piston et du clapet. L'ecoulement au niveau du clapet est assimile a un ecoulement radial visqueux. On etudie la loi de deformation du clapet (flexion d'un disque mince)

Etude d'une turbine radiale de turbocompresseur de suralimentation de moteur. Le calcul est base sur la resolution de l'equation de l'equilibre radial dans la section de sortie de la machine. On se limite a une approche monodimensionnelle de l'ecoulement. Etablissement experimental d'une cartographie des ecarts flux-profil en sortie de roue

Etude experimentale des proprietes de quelques corps poreux consolides ou non et de l'ecoulement autour et au travers de trois coques cylindriques poreuses. Etude theorique et numerique de l'ecoulement confine pour differentes conditions de raccordement. Etude par le calcul et l'experience de l'ecoulement lent au travers de milieux poreux representes par differentes structures de treillis de cylindres et regi par les lois de stokes et de brinkman. Mise en evidence de zones de recirculation dans ces milieux

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.

Understanding the mechanics of turbulent fluid flow is of key importance for industry and society as for example in aerodynamics and aero-acoustics. The massive computational cost for resolving all turbulent scales in a realistic problem makes direct numerical simulation of the underlying Navier-Stokes equations impossible. Recent advances in adaptive finite element methods offer a new powerful tool in Computational Fluid Dynamics (CFD). The computational cost for simulating turbulent flow can be minimized where the mesh is adaptively resolved, based on a posteriori error control. These adaptive methods have been implemented for efficient serial computations, but the extension to an efficient parallel solver is a challenging task. This work concerns the development of an adaptive finite element method for modern parallel computer architectures. We present efficient data structures and data decomposition methods for distributed unstructured tetrahedral meshes. Our work also concerns an efficient parallellization of local mesh refinement methods such as recursive longest edge bisection. We also address the load balance problem with the development of an a priori predictive dynamic load balancing method. Current results are encouraging with almost linear strong scaling to thousands of cores on several modern architectures.
QC 20110223

The efficient numerical approximation of viscous, incompressible flow by families of mixed finite elements is subject to the satisfaction of a stability or inf-sup condition between the velocity and pressure approximation spaces. The present work analyses the stability of mixed hp-finite elements for planar Stokes flow on affine quadrilateral meshes comprising of regular and anisotropic elements. Firstly, a new family of mixed hp-finite elements is presented for regular elements with an inf-sup constant bounded below independently of the mesh size h and the spectral order p. In particular, the element allows continuous piecewise polynomial pressures to be used. Next, the stability of families of mixed hp-finite elements on geometrically refined anisotropic elements is considered using a macro-element technique. New results are presented for edge and corner macro-elements, in particular, for the latter case, the dependence of the inf-sup constant on the geometric refinement parameter is explicitly characterised. The families are then used in the numerical approximation of two physical Navier-Stokes problems.

Viscoelastic fluid flow with immersed boundaries of complex geometry is widely found both in nature and engineering processes. Examples include haemocytes moving in human blood flow, self-propulsion of microscopic organisms in complex liquids, hydraulic fracturing with sand in oil flow, and suspension flow with viscoelastic medium. Computational modelling of such systems is important for understanding complex biological processes and assisting engineering designs. Conventional simulation methods use conformed meshes to resolve the boundaries of complex geometry. Dynamically updating the conformed mesh is computationally expensive and makes parallelization difficult. In comparison, Cartesian grid methods are more promising for large scale parallel simulation. Using Cartesian grid methods to simulate viscoelastic fluid flow with complex boundaries is a relatively unexplored area. In this thesis, a sharp interface Cartesian grid method (SICG) and a smoothed interface immersed boundary method (SIIB) are developed in order to simulate viscoelastic fluids in complex geometries. The SICG method shows a better prediction of the stress on stationary boundaries while the SIIB method shows reduced non-physical oscillations in the computation of drag and lift forces on moving boundaries. Parallel implementations of both solvers are developed. Convergence of the numerical schemes is shown and the implementations are validated with a few benchmark problems with both stationary and moving boundaries. This study also focuses on the simulation of flows past 2D cylindrical or 3D spherical particles. Lateral migration of particles induced by inertial and viscoelastic effects are investigated with different flow types. Equilibrium positions of inertia-induced migration are reported as a function of the particle Reynolds number and the blockage ratio. The migration in the viscoelastic fluid is simulated from zero elastic number to a finite elastic number. The inclusion of both inertial and viscoelastic effects on the lateral migration of a particle is the first of its kind. New findings are reported for the equilibrium positions of a spherical particle in square duct flow, which suggest the need for future experimental and computational work.

This thesis is concerned with the development of meshless methods using radial basis functions for solving fluid flow problems. The advantage of meshless methods over traditional mesh-based methods is that they make use of a scattered set of collocation points in the physical domain and no connec- tivity information is required. An important objective of the present research is to develop novel meshless methods for unsteady flow problems. Symmetric/unsymmetric radial basis function collocation schemes are proposed for solving an unsteady convection-diffusion equation for various Peclet numbers. Both global and compactly supported radial basis functions are used and the convergence behaviours of various radial basis functions are studied. The performance of the presented schemes is shown by using both uniform as well as scattered distribution of points. Numerical results suggest that these schemes are capable of obtaining accurate results for low and medium Peclet numbers. Next, two directions have been explored in this thesis for using radial basis functions to solve large scale problems encountered in fluid flow problems. They are namely, domain decomposition schemes and radial basis functions in finite difference mode. These schemes are shown to be computationally efficient and also aid in circumventing the ill-conditioning problem. The performance of both schemes are evaluated by solving the unsteady convection-diffusion problem. The last part of this thesis is concerned with the solution of the 2D Navier-Stokes equations. Meshless methods based on radial basis collocation and scattered node finite difference schemes are formulated for solving steady and unsteady incompressible Navier-Stokes equations. A novel ghost node strategy is proposed for incor- porating the no-slip boundary conditions. Optimisation strategies based on residual error objective and leave-one-out statistical criterion are proposed to evaluate the optimal shape parameter value in case of the multiquadric RBF for collocation and scattered finite difference approaches respectively. Standard benchmark problems like the driven cavity flows in square and rectangular domains and backward facing step flow problem are solved to study the performance of the developed schemes. Finally, a higher order radial basis function based scattered node finite difference method is proposed for solving the incompressible Navier-Stokes equations.

A series of experiments has been conducted for comparison with the results of a computer code called CHYMES. It is intended to calculate the coarse mixing of molten metal with water by solving the equations of the Separated Flow Model. These are derived by volume averaging and the terms that relate them to the particular case of participate flow are discussed. An experimental apparatus that is compatible with CHYMES and coarse mixing has been constructed which projects a jet of ball bearings into a thin tank of water. Experiments over a wide range of conditions were conducted at room temperature. Owing to practical difficulties only one, poorly controlled experiment with hot ball bearings was performed. Under nearly all sets of conditions an arrow-shaped plume was obtained. The speed of penetration of the plume varied little with changes in experimental conditions. The width of the plume was most strongly influenced by the widths of the tank and the jet. The individual paths of some particles were followed; it appeared that their motion was mostly dependent on their position in the plume. A model of the plume is proposed, based upon its front being impermeable to water in the vertical direction. Much of the detail of the experimental plumes was not present in the computational results and they responded differently to changes in conditions. It is proposed that this is a result of the different forms of the two sets of plumes. To rectify this an experimental plume was volume averaged. A method to determine a suitable averaging volume size is described. The process results in a plume similar to the computational ones. The length scales required for volume averaging to be successful are discussed and the possibility that this method is inappropriate for describing coarse mixing is admitted.

An experimental investigation of non-uniform flow past a 1.615 foot, 3-bladed propeller was conducted in the Virginia Tech 6 foot by 6 foot Stability Wind Tunnel. The free stream velocity was 44.5 ft/sec and the propeller rpm 1400. A screen disk consisting of two circular meshes, one 15 inches in diameter and the other 5, along with a 30 degree wedge having a 7.5 inch radius, was used to create the non-uniform inflow. The screen disk was chosen to simulate a wake flow behind a slender body with an attached appendage. The propeller was operated at self-propelled mode with respect to the drag of the screen disk. Several types of measurements were completed on the propeller and the near wake. First, the propeller performance quantities were measured. The second type of measurements were the mean flow quantities, which included the mean velocities and static pressures. These were obtained by using a five hole yawhead probe. The third type of measurements were made with an x-wire probe, constant temperature anemometer and an r.m. s. meter. These allowed all the turbulence quantities, intensities and shear stresses, to be obtained. All turbulence quantities were averaged in the peripheral direction. The results of the mean and turbulent flow under the non-uniform flow condition are documented and discussed in detail. The 3-D non-uniform inflow caused the location of the maximum thrust to be shifted from . 7R, previously found for uniform inflow for the same propeller, to .88R while the location of maximum swirl was shifted inward from .6R to .5R. The turbulence quantities were sensitive to the non-uniform mean inflow and the upstream turbulence created by the screen disk, especially in the wake of the wedge region. This was generally observed in the form of higher turbulence intensities and shear stresses. This data can be used to verify and refine turbulent transport models and computational methods for flows of this type.
M.S.

Transport phenomena inside a low consistency disc refiner were experimentally investigated. A transparent refiner door was designed and fabricated with four acrylic viewports enabling plate-scale and groove-scale visual observation. High speed video, ultra-violet fluorescent tracer particles and a MATLAB program were used to perform particle tracking velocimetry to gain further understanding of the flow field. The experimental working fluid under study was water. The effects of refiner operating parameters on the flow field were of particular interest. Refiner flow rates were varied from 300 to 700 litres per minute. Refiner rotational speeds were varied from 400 to 1200 RPM. Plate gap values under study included 7.5, 2.5, 1.5, and 0.75 mm. Two plate configurations were studied, including a smooth rotor and grooved rotor with a machined acrylic stator plate. The plate geometry under test was designed for softwood pulp having a bar edge length equal to 0.99 km/rev. A set of phenomenological characterizations of observed particle behaviour was identified. Qualitative results were provided for the effect of gap, refiner speed, and flow rate on the flow field. Lagrangian pathlines were shown to reveal tortuous flow for grooved rotor experiments. Quantitative results were presented for grooved rotor experiments for gaps of 0.75 mm. Eulerian measurements of groove axial velocity indicated fluid transport into and out of the stator grooves, while net transport occurred out of the grooves. The presence of backflow in the stator grooves was observed at all operating points for the grooved rotor under test. The relationship between stator backflow velocity and operating parameters was reported showing an increase with refiner speed and a minimal decrease with refiner flow rate. It has been shown that there is a linear relationship between stator backflow velocities and the pressure differential across the refiner. Rotational motion in the stator grooves was quantified by angular velocity and turnover rate of the fluid. Turnover rate was defined as the number of rotations of the fluid as it travels the length of the groove. Angular velocity increased proportionally with refiner speed and turnover rate did not vary significantly with refiner operating parameters.

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.

This Thesis is about the application of coupled multigrid solvers to the numeri- cal simulation of viscous incompressible fluids. In the centre of discussion is the adaptivity between a one-dimensional solver and a two-dimensional one. The methodology used has proved highly successful for single-and multi-phase laminar flows, leading to solution algorithms that are robust, efficient and accu- rate. The solvers presented here required a considerable number of algorithmic developments. Some of them have demanded the use of some well-known software packages. The Thesis outline is as follows: firstly, the modelling of transient single-phase and multi-phase flows is reviewed, together with a brief overview of the numerical schemes and multigrid methods used in the solvers. Secondly, the Navier-Stokes governing equations are presented and the space discretization formulas based on a control volume are formulated. After having specified the solution algorithms we present results for each solver for a set of test cases of varying complexity. Com- parison with our reference commercial code is outlined, showing good agreement in the results. Interpolation transfer operators used in the interface between the one-dimensional solver and the two-dimensional one are addressed. The coupled solvers are then applied on the numerical simulation of the transient flows on two complex multi- domain problems. Comparison results with the two-dimensional solvers have been performed. The question of performance and accuracy is addressed in detail, both in terms of robustness and speed of convergence. Good accelerations are obtained using the coupled solver. The CPU-time spent to reach the expected steady-state solution is about ten to thirty five percent of the equivalent two-dimensional solver. Considerable gains in memory usage have been achieved. The robustness has been easily verified in the comparison process with the two-dimensional transient solvers. Analytic solutions have been formulated and discussed. However some dependence on the Reynolds numbers has been observed. This was due to the geometric constraints of the complex test cases and the change of some fluid properties.

The objective of the thesis is to develop a numerical tool to describe how the concentration of one or more substances distributed in a fluid environment changes under the effect of three transport processes: advection, diffusion and absorption. For that purpose, it is essential to know the interaction of the transported substance with the fluid medium. The thesis aims to develop stabilized numerical methods for solving the transport and fluid flow equations in a coupled manner for greater accuracy, efficiency and speed when predicting the motion of the transported substances in the fluid. Emphasis is put in the transport of substances in fluids at high Péclet numbers. The practical motivation of the work is predicting the transport of a pollutant in air in urban environments. The thesis document summarizes the research published in three papers published in JCR journals of high impact. The author of the thesis is also the first author in the three papers. The papers are attached to the document in the corresponding chapters. The description of the thesis developments has been organized as follows. First, we present the research carried out in the thesis for the development of a generalized stabilized Finite Increment Calculus-Finite Element Method (FIC--FEM) formulation for solving the multidimensional transient advection-diffusion-absorption equation. The starting point of the developments are the governing equations for the multidimensional steady advection-diffusion-absorption and the unidimensional transient advection-diffusion-absorption problems obtained via the FIC procedure. The good behaviour of the new FIC--FEM formulation is shown in several examples of application. This work was published in the first of the three papers mentioned. In the following chapter we present an innovative numerical method for solving transport problems with high values of advection and / or absorption. A Lagrangian approach based on the updated version of the classical Particle Finite Element Method (PFEM) has been developed to calculate the advection of substances in fluids, while a Eulerian strategy based on the stabilized FIC--FEM formulation is adopted to compute diffusion and absorption effects. The new semi-Lagrangian approach has been validated in its application of a series of academic examples of transport of substances for different values of the Péclet and Damköhler numbers. Finally, we derive a procedure for coupling the fluid and transport equations to model the distribution of a pollutant in a street canyon. In our case, we have considered black carbon (BC) as the pollutant. The evolution of the fluid flow is calculated with a standard stabilized finite element method using the Quasi-Static Variational Multiscale (QS-VMS) technique. For the temperature and pollutant transport we use the semi-Lagrangian procedure developed in the thesis. Several examples of application have been solved to illustrate the accuracy and practicability of the proposed numerical tool for predicting the transport of a pollutant in air in urban environments. One of the examples are presented in the third paper, while another academic one is presented in the appendix of this document.
El objetivo de la tesis es desarrollar una herramienta numérica para describir cómo cambia la concentración de una o más sustancias distribuidas en un medio fluido bajo el efecto de tres procesos de transporte: advección, difusión y absorción. Para ello, es fundamental conocer la interacción de la sustancia transportada con el medio fluido. La tesis pretende extender métodos numéricos estabilizados para resolver las ecuaciones de transporte y flujo de fluidos de manera acoplada para una mayor precisión, eficiencia y velocidad a la hora de predecir el movimiento de las sustancias transportadas en el fluido. Se hace hincapié en el transporte de sustancias en fluidos con números de Péclet elevados. La motivación práctica del trabajo es predecir el transporte de un contaminante en el aire en entornos urbanos. El documento de tesis resume la investigación publicada en tres artículos publicados en revistas de alto impacto del JCR en los cuales el autor de la tesis también es el primer autor. Los trabajos se adjuntan al documento en los capítulos correspondientes. La descripción de los desarrollos de tesis se ha organizado de la siguiente manera. En primer lugar, presentamos la investigación realizada en la tesis para el desarrollo de una formulación generalizada estabilizada de cálculo de incrementos finitos - método de elementos finitos (FIC--FEM) para resolver la ecuación transitoria multidimensional advección-difusión-absorción. El punto de partida son las ecuaciones que gobiernan los problemas multidimensionales estacionarios de advección-difusión-absorción y los problemas de advección-difusión-absorción unidimensionales transitorios obtenidos mediante el procedimiento FIC. El buen comportamiento de la nueva formulación FIC--FEM se muestra en varios ejemplos de aplicación. Este trabajo fue publicado en el primero de los tres artículos mencionados. En el siguiente capítulo presentamos un método numérico innovador para resolver problemas de transporte con altos valores de advección y / o absorción. Se ha desarrollado un enfoque lagrangiano basado en la versión actualizada del método clásico de elementos finitos de partículas (PFEM) para calcular la advección de sustancias en fluidos, mientras que se adopta una estrategia euleriana basada en la formulación estabilizada FIC--FEM para calcular los efectos de difusión y absorción. El nuevo enfoque semilagrangiano ha sido validado mediante su aplicación en una serie de ejemplos académicos de transporte de sustancias para diferentes valores de los números de Péclet y Damköhler. Finalmente, derivamos un procedimiento para acoplar las ecuaciones de fluido y transporte para modelar la distribución de un contaminante en una calle. En nuestro caso, hemos considerado el carbono negro (BC) como contaminante. La evolución del flujo de fluido se calcula con un método estándar de elementos finitos estabilizados utilizando la técnica Quasi-Static Variational Multiscale (QS-VMS). Para la temperatura y el transporte de contaminantes utilizamos el procedimiento semilagrangiano desarrollado en la tesis. Se han resuelto varios ejemplos de aplicación para ilustrar la precisión y viabilidad de la herramienta numérica propuesta para predecir el transporte de un contaminante en el aire en entornos urbanos. Uno de los ejemplos se presenta en el tercer artículo, mientras que otro académico se presenta en el apéndice de este documento.
Enginyeria civil

The accurate prediction of pipe contraction pressure loss is important in the design of pipe system such as heat exchangers, particularly when close control of the flow distribution in a network of pipes is required. The prediction of contraction pressure loss depends heavily on experimental data. Large discrepancies in these predictions are evident in the literature. Experimental results giving pres!? re loss coef fici ents for a range of Reyno 1 ds numbers of 4x 10 -2x 10 and area ratios of 0.135 - 0.692 are presented and compared with predictions from a method developed that allows for velocity profile variation through the contraction. The results show a Reynolds number dependence and good agreement between predicted and measured values. It is also important to be able to predict the variation of pressure loss coefficient with variations in the small-bore inlet geometry, referred to as the inlet sharpness. There are no know experimental data for the effects of inlet sharpness on the pipe contraction loss coefficient, but there are data for intakes set flush in a plane wall which are used as approximations. Experimental data showing the variation of pressure loss coefficient with inlet sharpness up to 13.4% are presented and compared with approximate data. The comparison shows significant differences. A three beam laser doppler anemmeter has been used to measure the detailed flow field for an area ratio of 0.332 and a Reynolds number of 153.8 x 10. The mean velocity, turbulent intensity and Reynolds stress distributions are presented for twenty-two axial stations between four large-bore diameters upstream to fourteen small-bore diameters downstream of the contraction. These experimental measurements are compared with computer predictions using the FLUENT code with the k-e- turbulence model. The general trends in the flow are predicted, however there are significant differences in the detailed flow field which are highlighted.

This research presents an approach to accurately simulate flow experiments through a fractured core using experimental, stochastic, and simulation techniques. Very often, a fracture is assumed as a set of smooth parallel plates separated by a constant width. However, the flow characteristics of an actual fracture surface are quite different, affected by tortuosity and the impact of surface roughness. Though several researchers have discussed the effect of friction on flow reduction, their efforts lack corroboration from experimental data and have not converged to form a unified methodology for studying flow on a rough fracture surface. In this study, an integrated methodology involving experimental, stochastic, and numerical simulations that incorporate the fracture roughness and the friction factor is shown to describe flow through single fractures more efficiently. Laboratory experiments were performed to support the study in quantifying the flow contributions from the matrix and the fracture. The results were used to modify the cubic law through reservoir simulations. Observations suggest that the fracture apertures need to be distributed to accurately model the experimental results. The methodology successfully modeled fractured core experiments, which were earlier not possible using the parallel plate approach. A gravity drainage experiment using an X-ray CT scan of a fractured core has also validated the methodology.

Thorough analysis of drag and power characteristics of hydrodynamic power turbines is necessary for the efficient extraction of energy available at sea. In an effort to obtain these characteristics for a three-bladed, axial-flow hydroturbine, used to provide electric power on small sailing vessels, a load cell and voltage measuring system was installed on a carriage in a towing tank for analysis across a speed range of 0.5 to 1.8 m/s. A high-speed camera was used to determine the precise carriage speed and the rotational speed of the turbine rotor. For validation of concept, two thin flat plates were analyzed using the same drag force measuring system in the tow tank to compare experimentally determined drag coefficients with known literature values. Results are shown for the drag force experienced by the flat plates and both the non-rotating and the rotating turbine configurations. Additional results are shown for the turbines power generation capabilities at rotational speeds between 90 and 500 RPMs. Using computational fluid dynamics for the rectangular flat plate and non-rotational turbine configuration, the experimental and computational results for the drag force characteristics were compared.

In this thesis I develop and test new numerical methods for the numerical modelling of flow in highly heterogeneous and fractured reservoirs. We present the governing equations for immiscible two-phase fluid flow in a slightly compressible porous medium with capillary pressure. We discretize these equations using the node control volume finite element (NCVFE) method. The NCVFE method solves the pressure at the vertices of elements, and the control volumes are constructed around them. We present a numerical study of the method to test its accuracy in modelling multi-phase fluid flow in heterogeneous systems. Particularly, we study the performance of the method in domains with large contrasts in their material properties such as fractures, sealing or conductive faults, and highly heterogeneous reservoirs. We also present a study on the effects of petro-physical properties on the oil recovery for fractured reservoirs such as the permeability contrast between the fractured and matrix regions and the presence of capillary pressure in the matrix. We then present a new numerical method to overcome the limitations of the current NCVFE approach. The new method is called the interface control volume finite element (ICVFE) method. The method drastically decreases the smearing effects observed in the NCVFE method, while being mass conservative and numerically consistent. The pressure is computed at the interfaces of elements, and the control volumes are constructed around them. Its accuracy and convergence are benchmarked using three-dimensional tetrahedron elements for various complex cases. We show ICVFE is more accurate for modelling multi-phase flow in highly heterogeneous and fractured reservoirs than NCVFE. Furthermore, we present a new upstream mobility calculation method for NCVFE that improves the modelling for multi-phase fluid flow problems.

The air flow inside the crankcase of an internal combustion engine and the resistance that the air inside the engine induces on the moving engine components results in a component of the parasitic power loss of the engine, reducing the power output and efficiency of the engine. While these air flows have been researched using computational fluid dynamics in previous studies, there was no significant research found which had investigated these flows experimentally. The aim of this research was to develop experimental equipment to visualise the air flows in the crankcase of an engine. Particle Image Velocimetry (PIV) was the method that was chosen to visualise these air flows because it enabled instantaneous flow fields to be measured on a cross section through the entire crankcase of the test engine without creating any disturbance to the flow being measured. The experimental equipment that was developed in this research consisted of an electric motor driven 450 cc single cylinder engine. The crankcase of the engine consisted of a transparent box structure to enable visualisation of the flow inside the crankcase. The internal engine components were designed to run without a lubrication system to prevent contamination of the air inside the crankcase or the transparent sides of the crankcase. Planar PIV flow visualisation was carried out on 3 parallel planes in the crankcase perpendicular to the crankshaft’s axis of rotation. Sets of multiple crankshaft angle resolved PIV measurements were compiled at eight evenly spaced crankshaft angles over a full engine rotation. PIV flow visualisations were repeated for engine speeds of 500 rpm, 900 rpm, and 1500 rpm in clockwise and counter clockwise directions. PIV results were post processed to produce two dimensional velocity vector, vorticity, temporal variability, and pressure maps of the flow field inside the crankcase on each of the planes where flow visualisation was captured. The results indicated that the most significant flows in the crankcase were driven by the reciprocating motion of the piston, which forced air to flow in and out of the crankcase through the breather ports. The interaction of the rotating crankshaft with the air in the crankcase only affected the air flow in the immediate vicinity of the crankshaft and had minimal effect on the bulk flow of air inside the crankcase, therefore reversal of the engine rotation only effected the air flow near the crankshaft. The velocity of the airflows in the crankcase increased proportionally with increasing engine speed in the range of engine speeds tested. While the PIV observations made were not specific to any particular production engine, the general characteristics of the air flows observed may be applied to improve future engine designs. The results from this project may assist in the reduction of crankcase parasitic pumping losses and the aeration of lubrication oil in future engine designs.

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第14147号
工博第2981号
新制||工||1442(附属図書館)
26453
UT51-2008-N464
京都大学大学院工学研究科都市環境工学専攻
(主査)教授 後藤 仁志, 教授 細田 尚, 准教授 牛島 省
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