Tesi sul tema "Flow"
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1
Al-Yarubi, Qahtan. "Phase flow rate measurements of annular flows". Thesis, University of Huddersfield, 2010. http://eprints.hud.ac.uk/id/eprint/9104/.
Testo completoAbstract (sommario):
In the international oil and gas industry multiphase annular flow in pipelines and wells is extremely important, but not well understood. This thesis reports the development of an efficient and cheap method for measuring the phase flow rates in two phase annular and annular mist flow, in which the liquid phase is electrically conducting, using ultrasonic and conductance techniques. The method measures changes in the conductance of the liquid film formed during annular flow and uses these to calculate the volumetric and mass flow rates of the liquid film. The gas velocity in the core of the annular flow is measured using an ultrasonic technique. Combined with an entrainment model and the liquid film measurements described above, the ultrasonic technique enables the volumetric flow rate of the gas in the core and the volumetric and mass flow rates of entrained liquid droplets to be measured. This study was based on experimental work and the use of modelling techniques. The practical investigation comprised a series of experiments conducted on a purpose built flow loop in which the test section was a Perspex pipe of 50mm ID. The experimental work was limited to two-phase air-water flow. The flow loop was specifically designed to accommodate the different instruments and subsystems designed in this investigation including bespoke flow meters and a film extraction system. Most flow loop controls were automated using a MATLAB program. Reference measurement of the total water flow rate was made using a calibrated turbine flow meter and of the air flow rate using a calibrated rotameter. For the combined ultrasonic/conductance method investigated in this thesis, the velocity of the gas in the core was found using a novel Ultrasonic Flow Meter (USFM). The positioning and arrangement of the transducers have never been used previously. The flow velocity of the liquid film and the thickness of the film were measured using a novel Conductance Flow Meter (CFM). The CFM measured the liquid film thickness using novel wall conductance probes. By cross correlating the signals from a pair of such probes the film velocity was obtained. Good agreement of the experimental results obtained from the CFM and USFM with results published in the literature was found. Although not investigated experimentally in the work described in this thesis, annular flows encountered in the oil industry may contain a liquid phase comprising a mixture of oil and water. For such flows, the volume fractions of the oil and water can be measured using an automated bypass system developed during this project. The bypass system periodically extracts part of the liquid film, measures its density and then releases the sample back into the pipeline. The liquid phase volume fractions are determined from this density measurement which can be performed more than once per minute. An entrainment model was developed, which is required by the ultrasonic/conductance flow metering technique described in this thesis, in which the mass fraction of the liquid flowing as entrained droplets in the core can be determined from the liquid film thickness and velocity measurements. A mathematical model was also developed to describe the properties of the liquid film, such as liquid velocity profile within the film, and the model’s results were found to agree with the experimental results obtained during the project and also with previous work cited in the literature. The complexity of this latter model was reduced by making a number of simplifying assumptions, which are presented and discussed in the thesis, including the assumption that in annular flow there is a dynamic balance liquid entrainment and droplets being deposited back onto the film. The combination of the designed CFM and USFM with the bypass tube and the entrainment model offer the opportunity for a ‘wet gas’ flow meter to be developed to measure two and three phase annular flows at relatively low cost and with enhanced accuracy. Such a device would have the advantage that it would by substantially smaller than systems using separators and it could even be retrofitted onto off-shore platforms. The integration of the subsystems developed in this project into a single system capable of giving on-line measurements of annular flow would be a major benefit to the author’s sponsor, Petroleum Development of Oman.
2
Murray, Nathan E. "Flow field dynamics in subsonic cavity flows /". Full text available from ProQuest UM Digital Dissertations, 2006. http://0-proquest.umi.com.umiss.lib.olemiss.edu/pqdweb?index=0&did=1299816381&SrchMode=1&sid=4&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1193667418&clientId=22256.
Testo completo
3
Bulathsinghala, Dinitha. "Afterbody vortex flows and passive flow control". Thesis, University of Bath, 2019. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767593.
Testo completoAbstract (sommario):
Experiments have been carried out in a wind tunnel in order to study the aerodynamics ofafterbody vortex flows pertinent to cargo aircraft with upswept afterbodies. The overallaim of the study was to understand detailed vortex flow physics, to examine passive flowcontrol methods for drag reduction, and to examine the flowfield with the cargo rampdoor deployed. The simplified wind tunnel models were axisymmetric slanted base cylinderswhich have previously been utilised for afterbody vortex flow generation and weretested at ReD = 200; 000. Drag force, 2D Particle Image Velocimetry (PIV) and surfacepressure measurements were conducted along with detailed flowfield analysis of PIV dataincluding unsteady aspects of the flow.
4
Langkau, Katharina. "Flows over time with flow dependent transit times". [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968912656.
Testo completo
5
Costigan, G. "Flow pattern transitions in vertical gas - liquid flows". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361925.
Testo completo
6
Gürcan, Fuat. "Flow bifurcations in rectangular, lid-driven, cavity flows". Thesis, University of Leeds, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425523.
Testo completo
7
Gissen, Abraham Naroll. "Active flow control in high-speed internal flows". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54865.
Testo completoAbstract (sommario):
Manipulation of high-speed duct flow by streamwise vorticity concentration that are
engendered by interactions of surface-mounted passive and active flow control actuators with the cross flow is investigated experimentally in a small-scale wind tunnel. The controlled formation of these streamwise vortices can be a key element in the mitigation of the adverse flow effects in
a number of applications including aero-optical aberrations owing to unsteady local transonic shocks, pressure recovery and distortion due to secondary flows in embedded propulsion system, thrusts reversal and augmentation for aerodynamic control. The effects of the actuation are
investigated using various converging-diverging inserts along one of the test section walls. Passive actuation includes micro-vanes and active actuation is effected using high-frequency, surface-mounted fluidic oscillators. Hybrid actuation is demonstrated by combining the passive
and active actuation approaches to yield a “fail-safe” device with significant degree of
controllability. The investigations consider the effects of the surface actuation in three
application areas namely, stabilization of transonic shocks, suppression of total-pressure distortion in offset ducts, and mitigation of separation in internal flow turning.
8
Paleo, Cageao Paloma. "Fluid-particle interaction in geophysical flows : debris flow". Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27808/.
Testo completoAbstract (sommario):
Small scale laboratory experiments were conducted to study the dynamic mor- phology and rheological behaviour of fluid-particle mixtures, such as snout-body architecture, levee formation, deposition and particle segregation effects. Debris flows consist of an agitated mixture of rock and sediment saturated with water. They are mobilized under the influence of gravity from hill slopes and channels and can reach long run-out distance and have extremely destructive power. Better understanding of the mechanisms that govern these flows is required to assess and mitigate the hazard of debris flows and similar geophysical flows. Debris flow models are required to accurately deal with evolving behaviours in space and time, to be able to predict flow height, velocity profiles and run-out distances and shapes. The evolution of laboratory debris flows, both dry glass beads and mixtures with water or glycerol, released from behind a lock gate to flow down an inclined flume, was observed through the channel side wall and captured with high speed video and PIV analysis to provide velocity profiles through out the flow depth. Pore pressure and the normal and shear stress at the base of the flow were also measured. Distinct regions were characterized by the non-fluctuating region and the in- termittent granular cloud surrounding the flows. The extent of these regions was shown to be related to flow properties. The separation of these two regions allowed the systematic definition of bulk flow characteristics such as characteristic height and flow front position. Laboratory flows showed variations in morphology and rheological characteristics under the influence of particle size, roughness element diameter, interstitial fluid viscosity and solid volume fraction. Mono-dispersed and poly-dispersed components mixed with liquids without fine sediments, reveal a head and body structure and an appearance similar to the classic anatomy of real debris flows. Unsaturated fronts were observed in mono-dispersed flows, suggesting that particle segregation is not the only mechanism. A numerical simulation of laboratory debris flows using the computer model RAMMS (RApid Mass Movements Simulation) was tested with dry laboratory flows, showing close similarity to calculated mean velocities.
9
Mehendale, Aditya. "Coriolis mass flow rate meters for low flows". Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/60164.
Testo completo
10
Lemée, Thomas. "Shear-flow instabilities in closed flow". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112038.
Testo completoAbstract (sommario):
Cette étude se concentre sur la compréhension de la physique des instabilités dans différents écoulements de cisaillement, particulièrement la cavité entraînée et la cavité thermocapillaire, où l'écoulement d'un fluide incompressible est assuré soit par le mouvement d’une ou plusieurs parois, soit par des contraintes d’origine thermique.Un code spectral a été validé sur le cas très étudié de la cavité entrainée par une paroi mobile. Il est démontré dans ce cas que l'écoulement transit d'un régime stationnaire à un instationnaire au-delà d'une valeur critique du nombre de Reynolds. Ce travail est le premier à donner une interprétation physique de l'évolution non monotonique du nombre de Reynolds critique en fonction du facteur d'aspect. Lorsque le fluide est entraîné par deux parois mobiles, la cavité entraînée possède un plan de symétrie particulièrement sensible. Des solutions asymétriques peuvent être observés en plus de la solution symétrique au-dessus d'une certaine valeur du nombre de Reynolds. La transition oscillatoire entre la solution symétrique et les solutions asymétriques est expliquée physiquement par les forces en compétition. Dans le cas asymétrique, l'évolution de la topologie permet à l'écoulement de rester stationnaire avec l'augmentation du nombre de Reynolds. Lorsque l'équilibre est perdu une instabilité se manifeste par l'apparition d'un régime oscillatoire dans l'écoulement asymétrique.Dans une cavité thermocapillaire rectangulaire avec une surface libre, Smith et Davis prévoient deux types d'instabilités convectives thermiques: des rouleaux longitudinaux stationnaires et des ondes hydrothermales instationnaires. L'apparition de ses instabilités a été mis en évidence à plusieurs reprises expérimentalement et numériquement. Alors que les applications impliquent souvent plus d'une surface libre, il semble qu'il y ait peu de connaissances sur l'écoulement thermocapillaire entraînée avec deux surfaces libres. Un film liquide libre soumis à des contraintes thermocapillaires possède un plan de symétrie particulier comme dans le cas de la cavité entrainée par deux parois mobiles. Une étude de stabilité linéaire avec deux profils de vitesse pour le film liquide libre est présentée avec différents nombres de Prandtl. Au-delà d'un nombre de Marangoni critique, il est découvert que ces états de base sont sensibles à quatre types d'instabilités convectives thermiques qui peuvent conserver ou briser la symétrie du système. Les mécanismes qui permettent de prédire ces instabilités sont également découverts et interpréter en fonction de la valeur du nombre de Prandtl du fluide. La comparaison avec les travaux de Smith et Davis est faite. Une simulation numérique directe permet de valider les résultats obtenus avec l'étude de stabilité de linéaireThis study focuses on the understanding of the physics of different instabilities in driven cavities, specifically the lid-driven cavity and the thermocapillarity driven cavity where flow in an incompressible fluid is driven either due to one or many moving walls or due to surface stresses that appear from surface tension gradients caused by thermal gradients. A spectral code is benchmarked on the well-studied case of the lid-cavity driven by one moving wall. In this case, It is shown that the flow transit form a steady regime to unsteady regime beyond a critical value of the Reynolds number. This work is the first to give a physical interpretation of the non-monotonic evolution of the critical Reynolds number versus the size of the cavity. When the fluid is driven by two facing walls moving in the same direction, the cavity possesses a plane of symmetry particularly sensitive. Thus, asymmetrical solutions can be observed in addition to the symmetrical solution above a certain value of the Reynolds number. The oscillatory transition between the symmetric solution and asymmetric solutions is explained physically by the forces in competition. In the asymmetric case, the change of the topology allows the flow to remain steady with increasing the Reynolds number. When the equilibrium is lost, an instability manifests by the appearance of an oscillatory regime in the asymmetric flow. In a rectangular cavity thermocapillary with a free surface, Smith and Davis found two types of thermal convective instabilities: steady longitudinal rolls and unsteady hydrothermal waves. The appearance of its instability has been highlighted repeatedly experimentally and numerically. While applications often involve more than a free surface, it seems that there is little knowledge about the thermocapillary driven flow with two free surfaces. A free liquid film possesses a particular plane of symmetry as in the case of the two-sided lid-driven cavity. A linear stability analysis for the free liquid film with two velocity profiles is presented with various Prandtl numbers. Beyond a critical Marangoni number, it is observed that these basic states are sensitive to four types of thermal convective instabilities, which can keep or break the symmetry of the system. Mechanisms that predict these instabilities are discovered and interpreted according to the value of the Prandtl number of the fluid. Comparison with the work of Smith and Davis is made. A direct numerical simulation is done to validate the results obtained with the linear stability analysis
11
KASLIWAL, AMIT. "FLOW SEPARATION CONTROL FOR CYLINDER FLOW AND CASCADE FLOW USING GENERATOR JETS". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1141413192.
Testo completo
12
Laurantzon, Fredrik. "Flow Measuring Techniques in Steady and Pulsating Compressible Flows". Licentiate thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26344.
Testo completoAbstract (sommario):
This thesis deals with flow measuring techniques applied on steady and pulsatingflows. Specifically, it is focused on gas flows where density changes canbe significant, i.e. compressible flows. In such flows only the mass flow ratehas a significance and not the volume flow rate since the latter depends onthe pressure. The motivation for the present study is found in the use of flowmeters for various purposes in the gas exchange system for internal combustionengines. Applications can be found for instance regarding measurements of airflow to the engine, or measurements of the amount of exhaust gas recirculation.However the scope of thesis is wider than this, since the thesis aims toinvestigate the response of flow meters to pulsating flows. The study is mainlyexperimental, but it also includes an introduction and discussion of several inindustry, common flow measuring techniques.The flow meters were studied using a newly developed flow rig, designedfor measurement of steady and pulsating air flow of mass flow rates and pulsefrequencies typically found in the gas exchange system of cars and smallertrucks. Flow rates are up to about 200 g/s and pulsation frequencies from 0 Hz(i.e. steady flow) up to 80 Hz. The study included the following flow meters:hot-film mass flow meter, venturi flowmeter, Pitot tube, vortex flowmeter andturbine flowmeter. The performance of these meters were evaluated at bothsteady and pulsating conditions. Furthermore, the flow under both steady andpulsating conditions were characterized by means of a resistance-wire basedmass flow meter, with the ability to perform time resolved measurements ofboth the mass flux ρu, and the stagnation temperature T0.Experiments shows that, for certain flow meters, a quasi-steady assumptionis fairly well justified at pulsating flow conditions. This means that thefundamental equations describing the steady flow, for each instant of time,is applicable also in the pulsating flow. In the set-up, back-flow occurred atcertain pulse frequencies, which can result in highly inaccurate output fromcertain flow meters, depending on the measurement principle. For the purposeof finding means to determine when back flow prevails, LDV measurementswere also carried out. These measurements were compared with measurementsusing a vortex flow meter together with a new signal processing technique basedon wavelet analysis. The comparison showed that this technique may have apotential to measure pulsating flow rates accurately.Descriptors: Flow measuring, compressible flow, steady flow, pulsating flow,hot-wire anemometry, cold-wire anemometry.QC 20101208
13
Wang, Yueping. "Flow-dependent corrosion in turbulent pipe flow". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq23972.pdf.
Testo completo
14
Boulay, Fabienne. "Suspension-flow modeling : curvilinear flows and normal stress differences". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11689.
Testo completo
15
Lawless, Mark R. "Junction flow systems : mechanics and implications for natural flows". Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396912.
Testo completo
16
Bhattacharyya, A. Acosta Allan J. "Internal flows and force matrices in axial flow inducers /". Diss., Pasadena, Calif. : California Institute of Technology, 1994. http://resolver.caltech.edu/CaltechETD:etd-03012005-141633.
Testo completo
17
LASAGNA, DAVIDE. "Flow physics and control of trapped vortex cell flows". Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2518621.
Testo completoAbstract (sommario):
The main objective of this work is to investigate on the physics and on the control of the flow in a Trapped Vortex Cell, often referred to as TVC in the following. A TVC is a cavity with a particular geometry, which is optimised to trap a vortical structure. This configuration has recently gained interest has a device to control the flow past thick airfoils, but fundamental research is still required to make this technique effective.
Specifically, a first goal of this work is to investigate on the fundamental physics of this flow, by studying the basic elements and the dominant phenomena. In fact, this flow field is the result of the complex interaction of several flows, such as the upstream boundary layer, the shear layer detaching from the cavity leading edge, the vortex core, and the boundary layer developing downstream. A further issue of interest addressed in this work is that related to the role of unsteadiness of the cell flow, and in particular of the shear layer, whose self-sustained oscillations are a common feature of open-cavity flows.
The understanding of the driving physical mechanisms of the base flow is required to successfully proceed in developing a control strategy aiming at the control of the flow, because it is necessary to manipulate this flow in order to make the TVC an effective control device. Therefore, a second goal is to study and compare two different control techniques targeting the cavity flow. The first of the two is steady suction of the flow in the cell and has been already applied in past researches, but some additional insight into its effects on the base flow is required. The second proposed control technique is open-loop control with a synthetic jet actuator, a more efficient device whose unsteady action can couple to or drive the relevant mechanisms of the flow. Furthermore, open-loop control studies with a synthetic jet are propaedeutic for closed-loop control of the flow, briefly investigated in the last part of research.
18
Kasliwal, Amit. "Flow separation control for cylinder flow and cascade flow using vortex generator jets". Cincinnati, Ohio : University of Cincinnati, 2006. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1141413192.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Cincinnati, 2006.Title from electronic thesis title page (viewed Apr. 18, 2006). Includes abstract. Keywords: Flow Separation; Low Pressure Turbine Cascade; LPT Cascade; Flow over Cylinder; Vortex Generator Jets; VGJ; Multiblock Grid. Includes bibliographical references.
19
Abdelwahab, Ahmed Farouk. "Through-flow model for fan/flow-resistance configurations". Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2002. http://wwwlib.umi.com/cr/syr/main.
Testo completo
20
Somoano, Rodríguez Miguel. "Performance and flow dynamics in cross-flow turbines". Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/553240.
Testo completoAbstract (sommario):
Aquesta tesi doctoral presenta l'estudi que l'autor va realitzar per comprendre l'efecte de l'angle pitch de la pala sobre les interaccions pala-estela que tenen lloc dins el rotor i, per tant, sobre el rendiment d'una turbina de flux creuat amb tres pales rectes.
En primer lloc, hem estudiat experimentalment el rendiment d'aquest tipus de turbina en un túnel de vent de capa límit. Ho vam fer per a diferents pitches fixos de les pales, i amb diferents nombres de Reynolds basats en el diàmetre de la turbina que cobreixen la regió de transició en què el parell produït per les pales va superar el parell resistiu oposat. La forma i els valors de la corba de rendiment van canviar dràsticament amb només un increment de l'angle pitch fix. Com més gran sigui el nombre de Reynolds, menor és el tip speed ratio òptim i més cap al toe-out es mou l'angle pitch ideal.
Posteriorment, vam estudiar experimentalment la dinàmica de flux dins el rotor per diferents pitches de la pala en un tanc d'aigua amb carro, usant Digital Particle Image Velocimetry. Els assajos es van realitzar a un nombre de Reynolds basat en el diàmetre de la turbina constant, i per a un rang de tip speed ratios. L'atenció se centra en l'anàlisi de les interaccions pala-estela dins el rotor. Angles toe-in i excessius toe-out s'han associat a baixos rendiments d'aquest tipus de turbines. La investigació ens ha permès relacionar les interaccions pala-estela amb les diferències de rendiment en aquest tipus de turbines, en funció del tip speed ratio i de l'angle pitch de la pala.Esta tesis doctoral presenta el estudio que el autor realizó para comprender el efecto del ángulo pitch de la pala sobre las interacciones pala-estela que tienen lugar dentro del rotor y, por lo tanto, sobre el rendimiento de una turbina de de flujo cruzado con tres palas rectas. En primer lugar, hemos estudiado experimentalmente el rendimiento de este tipo de turbina en un túnel de viento de capa límite. Lo hicimos para diferentes pitches fijos de las palas, y con diferentes números de Reynolds basados en el diámetro de la turbina que cubren la región de transición en la que el par producido por las palas superó al par resistivo opuesto. La forma y los valores de la curva de rendimiento cambiaron drásticamente con sólo un incremento del ángulo pitch fijo. Cuanto mayor sea el número de Reynolds, menor es el tip speed ratio óptimo y más hacia el toe-out se mueve el ángulo pitch ideal. Posteriormente, estudiamos experimentalmente la dinámica de flujo dentro del rotor para diferentes pitches de la pala en un tanque de agua con carro, usando Digital Particle Image Velocimetry. Los ensayos se realizaron a un número de Reynolds basado en el diámetro de la turbina constante, y para un rango de tip speed ratios. La atención se centra en el análisis de las interacciones pala-estela dentro del rotor. Ángulos toe-in y excesivos toe-out se han asociado a bajos rendimientos de este tipo de turbinas. La investigación nos ha permitido relacionar las interacciones pala-estela con las diferencias de rendimiento en este tipo de turbinas, en función del tip speed ratio operativo y del ángulo pitch de la pala.
This doctoral thesis presents the study that the author have carried out in order to understand the effect of the blade pitch angle on the blade-wake interactions that take place inside the rotor, and hence on the performance of a three straight bladed cross-flow turbine. Firstly, we have experimentally studied the performance of this kind of turbine in a boundary layer wind tunnel. We did it for different fixed blade pitches, and at different turbine diameter Reynolds numbers covering the transitional region in which the torque produced by the blades overtook the opposed resistive torque. Shape and values of the performance curve changed drastically with just an increment of the fixed pitch angle. The higher the Reynolds number, the lower the optimal tip speed ratio and the more towards toe-out the ideal pitch angle is moved. Afterwards, we study experimentally the flow dynamics inside the rotor for different blade pitches in a water towing tank, using planar Digital Particle Image Velocimetry. Tests were made at a constant turbine diameter Reynolds number, and for a range of tip speed ratios. The focus is given to the analysis of the blade-wake interactions inside the rotor. Toe-in and excessive toe-out angles have been associated to low performances of this type of turbines. The investigation has allowed us to relate the blade-wake interactions with the performance differences in this type of turbines, as a function of both the operational tip speed ratio and the blade pitch angle.
21
Engin, Erjona. "Dynamic Analysis Of Flow In Two Dimensional Flow". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609374/index.pdf.
Testo completoAbstract (sommario):
The Poiseuille Flow is the flow of a viscous incompressible fluid in a channel between two infinite parallel plates. The behaviour of flow is properly described by the well-known Navier-Stokes Equations. The fact that Navier-Stokes equations are partial differential equations makes their solution difficult. They can rarely be solved in closed form. On the other hand, numerical techniques can be applied successfully to the well-posed partial differential equations.
In the present study pseudo-spectral method is implemented to analyze the Poiseuille Flow. The pseudo-spectral method is a high-accuracy numerical modelling technique. It is an optimum choice for the Poiseuille flow analysis due to the flows simple geometry. The method makes use of Fourier Transform and by handling operations in the Fourier space reduces the difficulty in the solution. Fewer terms are required in a pseudo-spectral orthogonal expansion to achieve the same accuracy as a lower order method.
Karhunen-Loève (KL) decomposition is widely used in computational fluid dynamics to achieve reduced storage requirements or construction of relatively low-dimensional models. In this study the KL basis is extracted from the flow field obtained from the direct numerical simulation of the Poiseuille flow.
22
Fraunhofer, Wolfgang. "Asymmetrical flow field-flow-fractionation in pharmaceutical analytics". Diss., lmu, 2003. http://nbn-resolving.de/urn:nbn:de:bvb:19-84503.
Testo completo
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Su, Chih-Chun. "Flow characteristics and performance of mixed-flow turbines". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416862.
Testo completo
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Manshoor, Bukhari bin. "Fractal flow conditioners for orifice plate flow meters". Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.574554.
Testo completoAbstract (sommario):
The orifice plate flow meter is the most common form of differential pressure flow meter used in industry. The standard discharge coefficient, which is defined by both British Standard and [SO 5167, is only valid if the flow approaching the meter is perfectly settled and fully developed. However, in practical applications the flow approaching the orifice meter is often disturbed by pipe-fittings and consequently the measurements become inaccurate. Basically, the design of the orifice plate meters that are independent of the upstream disturbances is a main goal for orifice plate metering. Either using a long straight pipe, or a flow conditioner upstream of an orifice plate, usually achieves this goal. In this project the effect of the fractal flow conditioner for both standard and non-standard flow conditions has been investigated in an experimental rig and simulation work. The results of using a combination of the fratal flow conditioner and orifice plate for non-standard flow conditions including swirling flow and asymmetric flow show that this package can preserve the accuracy of metering up to the level required in the Standards. The simulation results also show that the device can be used as a part of a flow metering package that will considerably reduce installation lengths. According to the main idea to introduce a predetermined turbulence flow caused by a flow conditioner for orifice plate flow metering, author was introduced another type of flow conditioner known as a metal foam flow conditioner. Open-cell metal foams with a porosity of 78.8% was formed and fashioned as a flow conditioner. Again the experimental results using the metal foam flow conditioner showed this metal foam flow conditioner demonstrated a good performance in terms of removing swirl and producing a repeatedly same flow profile within a short distance downstream of the flow conditioner. Furthermore, the low pressure drop across the metal foam is another advantage of this flow conditioner where the pressure loss coefficient for this flow conditioner is approximately 2.5.
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FERREIRA, ANA LUISA AULER DA SILVA. "ULTRASONIC TECHNOLOGY IN FLOW MEASUREMENT OF INCOMPRESSIBLE FLOW". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=16724@1.
Testo completoAbstract (sommario):
O presente trabalho avalia a influência da instalação em medidores de vazão
ultrassônicos, utilizando simulação numérica. Foram apresentadas características
dos medidores ultrassônicos e questões sobre a configuração da modelagem do
escoamento que podem influenciar nos resultados numéricos. Foram descritos os
procedimentos utilizados para traçar as linhas e para calcular a velocidade média
no medidor e o erro de medição. Foi mostrado o efeito de uma curva, duas curvas
no mesmo plano e duas curvas em planos perpendiculares, em medidores
ultrassônicos de 1, 2, 3, 4, 5 e 8 canais, com diferentes arranjos. Também foi
analisado o efeito de um degrau no resultado do medidor ultrassônico por meio de
simulação de medidores 1 a 5 canais e por calibração de medidores de 3 canais.
Foram utilizados fatores, calculados pela razão entre a velocidade indicada pelo
medidor em um dado local e a velocidade que seria indicada pelo mesmo medidor
em escoamento completamente desenvolvido. Logo após uma curva, os fatores
para medidores de 1 canal variaram de 0,40 a 1,28; para medidores de 3 canais, de
0,5 a 1,42; e para medidores de 4 e 5 canais, as diferenças chegaram a ultrapassar
10%. A 20D após uma curva, medidores de 2 e 3 canais indicaram fatores de 0,9 a
1,08 e medidores de 4 e 5 canais, fatores de 0,99 a 1,04. Os parâmetros de
diagnóstico analisados não se mostraram eficazes e sua utilização não é
recomendada. Pela simulação, um degrau convergente de -4% gera diferenças na
ordem de 0,3% para medidores de 3 canais e, para degrau divergente de 4%, as
diferenças ultrapassam 0,5%. A diferença entre os resultados das calibrações com
e sem degrau ficou entre 0,18% a 0,3%. A simulação numérica é uma ferramenta
útil na análise dos medidores ultrassônicos e mostrou a sensibilidade desses
medidores a variações no perfil de velocidades.The present work evaluates the influence of the installation in ultrasonic flow meters, using numerical simulation. Ultrasonic meter characteristics and issues about the flow modeling configuration that may influence the numerical results were presented. Procedures used to draw the lines and to calculate the meter mean velocity and the measurement error were described. The effect of one curve, two curves at the same plane and two curves at perpendicular planes at 1, 2, 3, 4, 5 and 8-path meters with different arrangements were shown. Also, the effect of one step at the results of ultrasonic meters was analyzed by the simulation of 1 to 5-paths meters and by the calibration of a 3 path meters. Factors calculated by the ratio between the velocity indicated by the meter in a certain position and the velocity that would be indicated by the meter in a fully developed flow. Just after one curve, the factors for 1-path meters varied from 0.40 to 1.28; for 3-path meters, from 0.5 to 1.42; and for 4 and 5-path meters, the differences were higher than 10%. At 20D downstream of one curve, 2 and 3-path meters indicated factors equal to 0.9 and 1.08; and 4 and 5-path meters, factors equal to 0.99 to 1.04. The diagnostic parameters analyzed were not efficient and their use is not recommended. By the simulation, a convergent step of -4% generates differences about 0.3% for 3-path meters and for a divergent step -f 4%, the differences are higher than 0.5%. The differences between the calibration results with and without steps were from 0.18% to 0.3%. The numerical simulation is a useful tool in the ultrasonic meter analyses and showed the sensitivity of these meters to velocity profile variations.
26
Sobek, Daniel. "Microfabricated fused silica flow chambers for flow cytometry". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10262.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 107-116).
by Daniel Sobek.
Ph.D.
27
Ariyoshi, Gen. "Flow Characteristics of Lead-Bismuth Two-phase Flow". Kyoto University, 2019. http://hdl.handle.net/2433/242325.
Testo completo
28
Pal, S. "Understanding flow of solid in continuous flow reactors". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2019. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/5989.
Testo completo
29
Fält, Åsa. "Flow Office". Thesis, Linnéuniversitetet, Institutionen för design (DE), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-43554.
Testo completo
30
Armstrong, Holly. "Natural Flow". VCU Scholars Compass, 2006. http://scholarscompass.vcu.edu/etd/694.
Testo completoAbstract (sommario):
Nature never ceases to amaze me with momentary observations of fluid energy: the purposeful curvature of a blue heron's neck; the pattern of water as it sweeps across a rock sculpted by that very motion; the changing light and shadows created as wind blows through tall grasses. The spark of beauty in these moments lies in the energy that causes this constant change. To capture this energy, either potential or kinetic, and embody it through textures and flow of mass, is my essential goal as an artist.
31
Doup, Benjamin. "Experimental Investigation of Flow Structure Development in Air-water Two-phase Flows". The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1332514704.
Testo completo
32
Muld, Tomas W. "Analysis of Flow Structures in Wake Flows for Train Aerodynamics". Licentiate thesis, KTH, Mechanics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12746.
Testo completoAbstract (sommario):
Train transportation is a vital part of the transportation system of today anddue to its safe and environmental friendly concept it will be even more impor-tant in the future. The speeds of trains have increased continuously and withhigher speeds the aerodynamic effects become even more important. One aero-dynamic effect that is of vital importance for passengers’ and track workers’safety is slipstream, i.e. the flow that is dragged by the train. Earlier ex-perimental studies have found that for high-speed passenger trains the largestslipstream velocities occur in the wake. Therefore the work in this thesis isdevoted to wake flows. First a test case, a surface-mounted cube, is simulatedto test the analysis methodology that is later applied to a train geometry, theAerodynamic Train Model (ATM). Results on both geometries are comparedwith other studies, which are either numerical or experimental. The comparisonfor the cube between simulated results and other studies is satisfactory, whiledue to a trip wire in the experiment the results for the ATM do not match.The computed flow fields are used to compute the POD and Koopman modes.For the cube this is done in two regions of the flow, one to compare with a priorpublished study Manhart & Wengle (1993) and another covering more of theflow and especially the wake of the cube. For the ATM, a region containing theimportant flow structures is identified in the wake, by looking at instantaneousand fluctuating velocities. To ensure converged POD modes two methods toinvestigate the convergence are proposed, tested and applied. Analysis of themodes enables the identification of the important flow structures. The flowtopologies of the two geometries are very different and the flow structures arealso different, but the same methodology can be applied in both cases. For thesurface-mounted cube, three groups of flow structures are found. First groupis the mean flow and then two kinds of perturbations around the mean flow.The first perturbation is at the edge of the wake, relating to the shear layerbetween the free stream and the disturbed flow. The second perturbation isinside the wake and is the convection of vortices. These groups would then betypical of the separation bubble that exists in the wake of the cube. For theATM the main flow topology consists of two counter rotating vortices. Thiscan be seen in the decomposed modes, which, except for the mean flow, almostonly contain flow structures relating to these vortices.
QC 20100518
Gröna Tåget
33
Robinson, Christopher J. "End-wall flows and blading design for axial flow compressors". Thesis, Cranfield University, 1991. http://dspace.lib.cranfield.ac.uk/handle/1826/6929.
Testo completoAbstract (sommario):
The flow in multistage axial flow compressors is
particularly complex in nature because of the proximity of
moving bladerows, the growth of end-wall boundary layers and
the presence of tip and seal leakages and secondary flow.
The problems associated with these phenomena are at their
most acute in the latter, subsonic stages of the core
compressor, where Reynolds numbers are modest and the
blading has low aspect ratio. Indeed, much of the
inefficiency of axial stages is believed to be associated
with the interaction between blading and end-wall flows.
The fact that the end-wall flow phenomena result in
conditions local to the blade which are quite different
from those over the major part of the annulus was
appreciated by many of the earliest workers in the axial
turbomachinery field. However, experiments on blading
designs aimed specifically at attacking the end-loss have
been sparse.
This thesis includes results from tests of conventional
and end-bent blading in a four-stage, low-speed, axial
compressor, built specifically for the task, at a scale
where high spatial measurement resolution could be readily
achieved within the flowpath. Two basic design styles are
considered: a zero a0 stage with DCA aerofoils and a
low-reaction controlled-diffusion design with cantilevered
stators.
The data gives insight into the flow phenomena present in
'buried' stages and has resulted in a much clearer
understanding of the behaviour of end-bent blading. A
3D Navier-Stokes solver was calibrated on the two
low-reaction stators and was found to give good agreement
with most aspects of the experimental results. An improved
design procedure is suggested based on the incorporation
of end-bends into the throughflow and iterative use of the
3D Navier-Stokes solver.
34
Lovick, Jonathon. "Horizontal, oil-water flows in the dual continuous flow regime". Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1383486/.
Testo completoAbstract (sommario):
The research presented in this thesis is concerned with the flow behaviour of two-phase, liquid-liquid, oil-water flow through horizontal pipes. The test liquids used were oil (density 828kg/rn3, viscosity 6x iO 3 Pa s) and water, with experiments carried out in a purpose built test facility with a stainless steel pipe (internal dia. 38mm, length 8m). Visual observation of the flow was possible at low mixture velocities through a lm transparent pipe at the end of the test section. At higher mixture velocities local probes were used for flow pattern identification. These local probes were a conductivity probe for identifying the continuous phase, and a high frequency impedance probe for measuring local phase distribution. A dual sensor impedance probe was also developed for measuring local drop velocity and also the drop chord length distributions. Pressure gradient was also measured using a differential pressure transducer, and in-situ phase fractions were obtained using Quick Closing Valves. Experimental results show that the dual continuous flow regime, where both phases retain their continuity while there is mixing at the interface, dominates at all input oil fractions at low mixture velocities and intermediate oil fractions at high mixture velocities. In general the pressure drop of the two-phase mixture is lower than that of single phase oil. At higher mixture velocities a minimum in pressure gradient appeared at high oil fractions perhaps as a combination of the drag reduction phenomenon and the relative fraction of the oil and water layers in the pipe. At the highest mixture velocity this minimum was at the boundary of fully dispersed oil continuous flow with dual continuous flow. Velocity ratios are shown to increase with increasing oil fraction at low mixture velocities, with this trend reversing at high mixture velocities. These trends in the pressure gradient and velocity ratio can be explained using the phase distribution diagrams, with the interfacial curvature greatly affecting velocity ratio. Local chord length data shows that, in general, drop sizes decrease with increasing distance from the interface and that oil drops tend to be slightly larger than water drops. Mixture velocity did not significantly affect the drop size of either phase in dual continuous flow. A modified version of the two-fluid model was suggested for dual continuous flow that treats the upper and lower layers as dispersions and uses experimental entrainment to calculate their properties. Better predictions were obtained when friction factors that accounted for the drag reduction phenomenon were used to calculate wall shear stresses.
35
Walsh, Joseph Anthony. "Secondary flows and inlet skew in axial flow turbine cascades". Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6659/.
Testo completoAbstract (sommario):
This thesis presents a detailed experimental investigation of the effects of inlet skew on the secondary flows and losses in a linear cascade of high turning turbine rotor blades. The blade that was used was modified from its original design to give aerodynamic similarity in the cascade flow conditions. Three levels of inlet skew were investigated using pressure probe instrumentation and the surface oil flow technique of flow visualisation. The results have shown that inlet skew has a profound effect on the secondary flows and on the magnitude of the secondary losses. The flowfield of the cascade was modelled using several computer models. Although reasonable results were obtained with a fully viscous three-dimensional code the other models were unable to predict accurately the magnitude of the losses or even the relative effect of inlet skew on the losses. This thesis also presents measurements of the turbulent flowfield of a similar linear cascade. It was found that regions of high turbulent kinetic energy were associated with regions of high total pressure loss. It was also found that the mass averaged total pressure loss and turbulent kinetic energy followed similar distributions in the cascade.
36
Yan, Baoshe. "Fluid flow induced by oscillating bodies and flows in cyclones". Thesis, University of Leeds, 1991. http://etheses.whiterose.ac.uk/435/.
Testo completoAbstract (sommario):
In this thesis the following aspects have been investigated: (i) the numerical solutions for unsteady 2-dimensional, incompressible viscous fluid flows induced by a harmonically oscillating cascade, and (ii) the fluid flows in industrial cyclones and their separation efficiencies. In the first part of the thesis we deal with fluid flows induced by harmonically oscillating cascades of cylinders with different cross sectional shapes. Numerical solutions for large amplitude oscillations of a cascade of normal flat plates are obtained by using a finite-difference method and it is found that solutions are in good agreement with some related experimental results. For small amplitude oscillations a perturbation method, series truncation technique and finite-difference methods are used to obtain solutions for cascades of normal flat plates and square cylinders. By assuming that the streaming Reynolds number is 0(1) then the outer streaming flows for cascades of square cylinders, normal flat plates and circular cylinders are investigated numerically for the streaming Reynolds number Rs up to 70. Conformal mapping, grid generation and boundary element methods are used to deal with the different geometries in order to determine the outer potential flows. For small values of the streaming Reynolds number it is found experimentally that the flow remains symmetrical and the numerically predicted fluid flow is in good agreement with the experimental results. As the value of the streaming Reynolds number increases then it is found experimentally that the flow develops asymmetries and this occurs when 8
37
Yato, Hiroki. "Flow pattern transition in curvilinear shear flows of viscoelastic fluids". 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/131910.
Testo completo
38
Muhamedsalih, Yousif. "Two-phase flow meter for determining water and solids volumetric flow rate in vertical and inclined solids-in-water flows". Thesis, University of Huddersfield, 2014. http://eprints.hud.ac.uk/id/eprint/23741/.
Testo completoAbstract (sommario):
Multiphase flow can be defined as the simultaneous flow of a stream of two or more phases. Solids-in-water flow is a multiphase flows where solids and liquid are both present. Due to the density differences of the two phases, the results for such flow is often to have non-uniform profiles of the local volume fraction and local axial velocity for both phases in the flow cross-section. These non-uniform profiles are clearly noticeable in solids-in-water stratified flow with moving bed for inclined and horizontal pipelines. However in many industrial applications, such as oil and gas industry, food industry and mining industry, multiphase flows also exist and it is essentially important to determine the phase concentration and velocity distributions in through the pipe cross-section in order to be able to estimate the accurately the volumetric flow rate for each phase. This thesis describe the development of a novel non-intrusive flow meter that can be used for measuring the local volume fraction distribution and local axial velocity distributions of the continuous and discontinuous phases in highly non-uniform multiphase flows for which the continuous phase is electrically conducting and the discontinuous phase is an insulator. The developed flow meter is based on combining two measurement techniques: the Impedance cross correlation ICC technique and the electromagnetic velocity profiler EVP technique. Impedance cross correlation ICC is a non-invasive technique used to measure the local volume fraction distributions for both phases and the local velocity distribution for the dispersed phase over the pipe cross-section, whilst the electromagnetic velocity profiler EVP technique is used to v measure the local axial velocity profile of the continuous phase through the pipe cross-section. By using these profiles the volumetric flow rates of both phases can be calculated. A number of experiments were carried out in solid-in-water flow in the University of Huddersfield solids-in-water flow loop which has an 80 mm ID and an approximately 3m long working section. ICC and EVP systems were mounted at 1.6 m from the working section inlet which was inclined at 0 and 30 degree to the vertical. The obtained result for the flow parameters including phase volume fraction and velocity profiles and volumetric flow rates, have been compared with reference measurements and error sources of difference with their reference measurements have been identified and investigated.
39
Mushyam, Aditya. "Effects of flow control on flow past bluff bodies". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/398031.
Testo completoAbstract (sommario):
The aim of this Ph.D. thesis, "Effects of flow control on flow past bluff bodies" is to study and analyzes the effects of Flow Control on various aspects and proverbs of flow past bluff bodies. Flow control techniques are presently researched and studied across the world to gauge their effectiveness in altering flow properties and patterns in different flow scenarios. The inspiration for the present work is derived from automobile industry, as analyzing the flow over backward step and inclined step shall help in understanding the characteristics of the rear vehicle wake. Since a considerable percentage of the energy needed to propel the vehicle is dissipated by the vorticity generated in the rear of the vehicle, hence it is of utmost importance to understand the properties of the wake. In the present study various possibilities were explored for application and examine effectiveness of active flow control techniques in bluff bodies to increase the aerodynamic efficiency. The primary aim of the study is to reduce the drag acting on bluff bodies by determining an effective active flow control technique and configuration.
Two different kinds of Active Flow Control techniques have been used in this thesis namely, "Zero Net Mass Flow Actuator" and "Fluidic Actuator". The characteristics of laminar and turbulent boundary layer were analyzed and the effectiveness of flow control in delaying the detachment of the boundary layer was analyzed. Numerical simulation programs were developed in C language for simulating various cases in the thesis and a 3D LES turbulence modeling finite volume code was developed using Smagorinsky-Lilly model in C language for the simulating the flow over backward step in turbulence regime. All the numerical simulation codas were validated with previous research works. The thesis is divided into five chapters analyzing flow over square cylinder, backward step and inclined step geometries in 2D and 3D in laminar and turbulent regimesL'objectiu de aquesta tesi doctoral, "Effects offlow control on flow past bluff bodies", és estudiar i analitzar els efectes del control de flux sobre diferents aspectes del flux al voltant de cossos genèrics, Bluff bodies. Les tècniques de control de flux estan en la actualitat sota recerca a nivell mundial, doncs és necessari estudiar l'efectivitat del flux aportat sobre les propietats i els patrons vermiculars del corrent de flux principal. El present treball està inspirat en la indústria del automòbil, així l’anàlisi del flux sobre un esgraó o be una superfície inclinada, ha de permetre entendre les característiques de l'estela de flux a la part del darrera de un vehicle automòbil. Aquest estudi es especialment rellevant quan es considera que una quantitat important de l'energia necessària per desplaçar un vehicle es dissipa gràcies a les estructures vorticulars formades a la part de darrera del vehicle. En aquesta tesi s'han examinat diverses possibilitats de aplicació de les tècniques de control actiu de flux per millorar la efectivitat a l'hora de incrementar la eficiència aerodinàmica sobre cossos genèrics, Bluff bodies. La finalitat bàsica de aquest estudi, és reduir les forces de arrossegament sobre cossos genèrics, gràcies a la determinació de la tècnica de control de fluid més efectiva i la seva implementació pràctica. Dues tècniques diferents de control actiu de fluid han sigut avaluades en aquesta tesi, la definida per un actuador amb flux net nul, "Zero Not Mass Flow Actuator", i la definida per la utilització de un actuador amb un flux net positiu, o be actuador fluídic, "Fluidic Actuator". Les característiques de la capa límit laminar i turbulenta han sigut analitzades així com la efectivitat del control de flux respecte el desplaçament aigües avall del despreniment de la capa límit. Tots els programes utilitzats per toles les simulacions numèriques han sigut creats per el autor de la tesi en llenguatge C, per el que fa referència a les simulacions tridimensionals en règim turbulent, el model de turbulència LES implementat
40
Bogner, Christina. "Analysis of flow patterns and flow mechanisms in soils". Thesis, Bayreuth Bayreuth Center of Ecology and Environmental Research, 2009. http://d-nb.info/997214058/34.
Testo completo
41
Kim, Youngho. "Online traffic flow model applying dynamic flow density relations". [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964751909.
Testo completo
42
Åsén, Per-Olov. "Stability of plane Couette flow and pipe Poiseuille flow". Doctoral thesis, KTH, Numerisk Analys och Datalogi, NADA, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4368.
Testo completoAbstract (sommario):
This thesis concerns the stability of plane Couette flow and pipe Poiseuille flow in three space dimensions. The mathematical model for both flows is the incompressible Navier--Stokes equations. Both analytical and numerical techniques are used. We present new results for the resolvent corresponding to both flows. For plane Couette flow, analytical bounds on the resolvent have previously been derived in parts of the unstable half-plane. In the remaining part, only bounds based on numerical computations in an infinite parameter domain are available. Due to the need for truncation of this infinite parameter domain, these results are mathematically insufficient. We obtain a new analytical bound on the resolvent at s=0 in all but a compact subset of the parameter domain. This is done by deriving approximate solutions of the Orr--Sommerfeld equation and bounding the errors made by the approximations. In the remaining compact set, we use standard numerical techniques to obtain a bound. Hence, this part of the proof is not rigorous in the mathematical sense. In the thesis, we present a way of making also the numerical part of the proof rigorous. By using analytical techniques, we reduce the remaining compact subset of the parameter domain to a finite set of parameter values. In this set, we need to compute bounds on the solution of a boundary value problem. By using a validated numerical method, such bounds can be obtained. In the thesis, we investigate a validated numerical method for enclosing the solutions of boundary value problems. For pipe Poiseuille flow, only numerical bounds on the resolvent have previously been derived. We present analytical bounds in parts of the unstable half-plane. Also, we derive a bound on the resolvent for certain perturbations. Especially, the bound is valid for the perturbation which numerical computations indicate to be the perturbation which exhibits largest transient growth. The bound is valid in the entire unstable half-plane. We also investigate the stability of pipe Poiseuille flow by direct numerical simulations. Especially, we consider a disturbance which experiments have shown is efficient in triggering turbulence. The disturbance is in the form of blowing and suction in two small holes. Our results show the formation of hairpin vortices shortly after the disturbance. Initially, the hairpins form a localized packet of hairpins as they are advected downstream. After approximately $10$ pipe diameters from the disturbance origin, the flow becomes severely disordered. Our results show good agreement with the experimental results. In order to perform direct numerical simulations of disturbances which are highly localized in space, parallel computers must be used. Also, direct numerical simulations require the use of numerical methods of high order of accuracy. Many such methods have a global data dependency, making parallelization difficult. In this thesis, we also present the process of parallelizing a code for direct numerical simulations of pipe Poiseuille flow for a distributed memory computer.QC 20100825
43
Sundström, Elias. "Centrifugal compressor flow instabilities at low mass flow rate". Licentiate thesis, KTH, Mekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184869.
Testo completoAbstract (sommario):
Turbochargers play an important role in increasing the energetic efficiency andreducing emissions of modern power-train systems based on downsized recipro-cating internal combustion engines (ICE). The centrifugal compressor in tur-bochargers is limited at off-design operating conditions by the inception of flowinstabilities causing rotating stall and surge. They occur at reduced enginespeeds (low mass flow rates), i.e. typical operating conditions for a betterengine fuel economy, harming ICEs efficiency. Moreover, unwanted unsteadypressure loads within the compressor are induced; thereby lowering the com-pressors operating life-time. Amplified noise and vibration are also generated,resulting in a notable discomfort. The thesis aims for a physics-based understanding of flow instabilities andthe surge inception phenomena using numerical methods. Such knowledge maypermit developing viable surge control technologies that will allow turbocharg-ers to operate safer and more silent over a broader operating range. Therefore,broadband turbulent enabled compressible Large Eddy Simulation (LES) cal-culations have been performed and several flow-driven instabilities have beencaptured under unstable conditions. LES produces large amounts of 3D datawhich has been post-processed using Fourier spectra and Dynamic Mode De-composition (DMD). These techniques are able to quantify modes in the flowfield by extracting large coherent flow structures and characterize their relativecontribution to the total fluctuation energy at associated. Among the mainfindings, a dominant mode was found which describes the filling and emptyingprocess during surge. A narrowband feature at half of the rotating order wasidentified to correspond to co-rotating vortices upstream of the impeller faceas well as elevated velocity magnitude regions propagating tangentially in thediffuser and the volute. Dominant mode shapes were also found at the rotatingorder frequency and its harmonics, which manifest as a spinning mode shapelocalized at the diffuser inlet. From the compressible LES flow solution one can extract the acoustic infor-mation and the noise affiliated with the compressor. This enable through datacorrelation quantifying the flow-acoustics coupling phenomena in the compres-sor. Detailed comparison of flow (pressure, velocity) and aeroacoustics (soundpressure levels) predictions in terms of time-averaged, fluctuating quantities,and spectra is carried out against experimental measurements.QC 20160406
44
Wong, Wai-Lid. "Flow development and mixing in three phase slug flow". Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/7780.
Testo completo
45
Wongl, Li Shing. "Flow and heat transfer in buoyancy induced rotating flow". Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250118.
Testo completo
46
Basnet, Keshav. "Flow around porous barriers: fundamental flow physics and applications". Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1824.
Testo completoAbstract (sommario):
Investigating flow and turbulence structure around a barrier mounted on the ground or placed in its vicinity is a fundamental problem in wind engineering because of many practical applications related to protection against adverse effects induced by major wind storms (e.g., hurricanes) and snow events (e.g., snow fences used to reduce adverse effects of snow drifting on the roads). In this work the focus is on the case when the obstacle/barrier is porous and the shape of the obstacle is close to a high-aspect-ratio rectangular cylinder situated in the vicinity of the ground. The study employs a range of numerical and experimental techniques to achieve this goal that include 3D LES and 2D RANS numerical simulations, and RTK survey and 3D photogrammetry techniques to measure ground elevations and snow deposits in the field.
In the first part of the study, high-resolution large eddy simulations are used to understand the fundamental flow physics of flow past 2D solid and porous vertical plates with a special focus on describing the unsteady wind loads on the obstacle, vortical structure of the turbulent wake, spectral content of the wake, the separated shear layers and of the characteristics of the large-scale vortex shedding behind the plate, if present. Results show that LES can accurately predict mean flow and turbulence statistics around solid/porous cylinders. Then, a detailed parametric study of flow past vertical solid and porous plates situated in the vicinity of a horizontal bed is performed for the purpose of understanding changes in the mean flow structure, turbulence statistics and dynamics of large scale coherent structures as a function of the main nondimensional geometrical parameters (bottom gap for solid and porous plates, and porosity and average hole size of porous plates) and flow variables (e.g., bed roughness) that affect the wake flow. In particular, the LES flow fields allowed clarifying how the interactions between the bottom and the top separated shear layers change with increasing bottom gap and what is the effect of the bleeding flow on the interactions between the separated shear layers that determine the coherence of the large-scale eddies at large distances from the wake.
In the second part of the thesis, a novel methodology based on field monitoring of the snow deposits and RANS numerical simulations is proposed to improve the design of snow fences and in particular the design of lightweight plastic snow fences that are commonly used to protect roads in the US Midwest against the snow drifting. The goal of the design optimization procedure is to propose a snow fence design that can retain a considerable amount of snow within a shorter downwind distance compared to fences of standard design. A major contribution of the present thesis was the development of a novel non-intrusive image-based technique that can be used to quantitatively estimate the temporal evolution of the volume of snow trapped by a fence over long periods of time. This technique is based on 3-D close range photogrammetry. Results showed that this technique can produce estimations of the snow deposits of comparable accuracy to that given by commonly used methods. This is the first application of this type of techniques to measurements of the snow deposits.
47
Kerekes, Rudolf. "Electrolyte flow rate control for Hydrogen Bromine Flow Batteries". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263240.
Testo completoAbstract (sommario):
The need for energy storage solutions became more significant with the increasing penetration of renewable energy sources in the electricity grid. In the last decades, the flow batteries have gained increasing attention. They have several advantages compared to the conventional battery technologies. Among these, the Hydrogen Bromine Flow Batteries offer a low cost energy storage solution by using globally abundant materials, since Hydrogen and Bromine can be found in large quantities in the oceans. This study was conducted to find out the relation between electrolyte flow rate and electrochemical cell performance and to give a suggestion for dynamic flow rate control to maximize the battery system performance. First, a theoretical model was built to describe the behaviour of the system in various conditions. However, the lack of information of the parameters led the research towards experimental analysis. A small scale system with cell power range of 10 to 14 W and pump power range of 2.6 to 6.8 W was built for the experiments to analyse the cell power at different flow rate values (122 ml/min, 185 ml/min and 230 ml/min). Also, the aim was to observe the gains of using dynamic flow rate (122 ml/min and 230 ml/min used at specific periods of the cycles). The results show that for small scale systems there is no net positive energy gain due to the small power of the battery compared to the power of the pump. However, there were improvements found in battery capacity with 28 % increase, and in Coulombic efficiency with 2.47 % increase, if the largerflow rate was used. Furthermore, a 55% pumping energy saving was reached if the dynamic flow rate was used instead of constant maximum flow rate. In addition, a large scale system was designed, which would be able to integrate a PID control concept for dynamic flow rate control in kW scale batteries. Further work will be required for building and testing the proposed large scale system, which tend to model a commercial size Hydrogen Bromine Flow Battery.Behovet av energilagringslösningar blev mer betydande med den ökande penetrationen av förnybara energikällor i elnätet. Under de senaste decennierna har flödesbatterierna fått ökad uppmärksamhet. De harflera fördelar jämfört med konventionella batteriteknologier. Då väte och brom finns i stora mängder i haven, erbjuder vätebromflödesbatterier en billig lösning för energilagring genom att använda globalt rikligt förekommande material. Denna studie genomfördes för att ta reda på sambandet mellan elektrolytflödeshastighet och elektrokemisk cellprestanda och för att ge ett förslag för dynamisk flödeshastighetskontroll för att maximera batterisystemets prestanda. Först byggdes en teoretisk modell för att beskriva systemets beteende under olika förhållanden. Emellertid ledde bristen på information om parametrarna forskningen mot experimentell analys. Ett småskaligt system med celleffektintervall från 10till 14 W och pumpeffektintervall på 2.6 till 6.8 W byggdes för experimenten för att analysera celleffekten vid olika flödeshastighetsvärden (122 ml / min, 185 ml / min och 230 ml / min). Syftet var också att observera vinsterna med att använda dynamisk flödeshastighet (122 ml / min och 230 ml / min använd vidspecifika perioder av cyklerna). Resultaten visar att för småskaliga system finns det ingen nettopositiv energivinst på grund av batteriets lilla effekt jämfört med pumpens effekt. Det fanns emellertid förbättringari batterikapacitet med en ökning på 28% och i Coulombic effektivitet med en ökning på 2.47% om den större flödeshastigheten användes. Det uppnåddes även en energibesparing på 55% om den dynamiska flödeshastigheten användes istället för konstant maximal flödeshastighet. Dessutom utformades ett storskaligt system som skulle kunna integrera ett PID-kontrollkoncept för dynamisk flödeshastighetskontroll i kW-skalbatterier. Ytterligare arbete kommer att krävas för att bygga och testa det föreslagna storskaliga systemet, som tenderar att modellera ett kommersiellt vätebromflödesbatteri.
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Salvini, Fabio <1992>. "Flow logic based information flow analysis of Android applications". Master's Degree Thesis, Università Ca' Foscari Venezia, 2018. http://hdl.handle.net/10579/12996.
Testo completoAbstract (sommario):
Android is the world's most popular mobile OS, with more than 2 billion monthly active devices. Static analysis is an essential tool to protect the sensitive data stored in the devices from malicious applications. In this thesis, we present the first flow logic for the information flow analysis of Dalvik bytecode that is specifically tailored to the peculiar lifecycle of Android applications. A prototype implementation based on a state-of-the-art SMT solver demonstrates the practicality of our approach.
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Kosakowski, Cindy. "Betydelsen av flow i bildskapande och pedagogers betydelse för flow : En uppsats inom bildpedagogik om flow och kreativitet och vilka förutsättningar som gynnar flow". Thesis, Högskolan i Gävle, Avdelningen för kultur-, religions- och utbildningsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-14630.
Testo completo
50
Chen, Jui-Yen, e 陳睿彥. "Flow-Depth Velocity Distribution Equationsfor Open Channel Flows". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/49242144806671080582.
Testo completoAbstract (sommario):
碩士國立成功大學
水利及海洋工程學系碩博士班
91
The log-low flow-depth velocity distribution equations for open channel flow and the Coles’ wake-flow function were reviewed wake-strength coefficient in the wake function at various flow conditions were compared. The result reveals that the values of are presented by previous investigators between -0.27 and 0.65. It is also found that Cloes’s revised wake-flow function can not well describe the velocity distributions for some open channel flows which are influenced by the pressure gradient and the side-wall-effects. We propose a method to overcome the problem. The velocity distribution is divided into upper region and lower region at the basis on the depth where the maximum velocity. When the two coefficients are the same which to be equal to the Cloes revised wake-flow function. Comparison of the proposed double-layer velocity distribution with measured data by Cloemen(1981) and Kirkgoz and Ardiclikglu(1997). The results show that the present proposed method can well describe the velocity distributions, with between 0.9 and 1.6 and between -0.02 and 0.69. Besides, the modified functions for the power-low equation are also investigated in the present study. A modified function F(y/ )= is proposed for the power-low velocity distribution, and compared with the measured data. It shows that the revised power-low equation can well describe the velocity distribution. Based on Coleman’s data , and the velocity correction is between 0.15 and 0.28, and proportional with the vertically averaged volumetric sediment concentration.