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1
Pitts, Katie Lynn. « Rheological and Velocity Profile Measurements of Blood in Microflow Using Micro-particle Image Velocimetry ». Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24038.
Texte intégralRésumé :
Microhemodynamics is the study of blood
flow in small vessels, usually on the order of
50 to 100 µm. The in vitro study of blood
flow in small channels is analogous to the in
vivo study of the microcirculation. At this scale the Reynolds and Womersly numbers
are significantly less than 1 and the viscous stress and pressure gradient are the main
determinant of flow. Blood is a non-homogeneous, non-Newtonian fluid and this complex composition and behavior has a greater impact at the microscale. A key parameter is the shear stress at the wall, which is involved in many processes such as platelet activation,
gas exchange, embryogenesis and angiogenesis. In order to measure the shear rate in
these blood flows the velocity profile must be measured. The measured profile can be characterized by the maximum velocity, the flow rate, the shear rate at the wall, or a shape parameter reflecting the bluntness of the velocity profile.
The technique of micro-particle image velocimetry (µPIV) was investigated to measure the velocity profiles of blood microflows. The material of the channel, the type of tracer particles, the camera used, and the choice in data processing were all validated to improve the overall accuracy of µPIV as a blood microflow measurement method. The knowledge gained through these experiments is of immediate interest to applications such as the design of lab-on-a-chip components for blood analysis, analysis of blood flow behavior, understanding the shear stress on blood in the microcirculation and blood substitute analysis.
Polymer channels were fabricated from polydimethylsiloxane (PDMS) by soft lithography
in a clean room. PDMS was chosen for ease of fabrication and biocompatibility. The contacting properties of saline, water, and blood with various polymer channel materials
was measured. As PDMS is naturally hydrophilic, surface treatment options were explored. Oxygenated plasma treatment was found to be less beneficial for blood than for water.
The choice of camera and tracer particles were validated. Generally, for in vivo studies, red blood cells (RBCs) are used as tracer particles for the µPIV method, while for in vitro studies, artificial fluorescent micro particles are added to the blood. It is demonstrated here that the use of RBCs as tracer particles creates a large depth of correlation (DOC), which can approach the size of vessel itself and decreases the accuracy of the method. Next, the accuracy of each method is compared directly. Pulsed images used in conjunction with fluorescing tracer particles are shown to give results closest to theoretical approximations. The effect of the various post-processing methods currently available were compared for accuracy and computation time. It was shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. Using the greatest amount of correlation window overlap with elongated windows aligned with the flow was shown to give the best results when coupled with a image pre-processing method previously published for microflows of water.
Finally the developed method was applied to a relevant biomedical engineering problem: the evaluation of blood substitutes and blood viscosity modifiers. Alginate is a frequently used viscosity modifier which has many uses in industry, including biomedical applications. Here the effect of alginate on the blood rheology, i.e., the shape of the velocity profile and the maximum velocity of blood
flow in microchannels, was investigated. Alginate was found to blunt the shape of the velocity profile while also decreasing the shear rate at the wall.
Overall, the accuracy of µPIV measurements of blood flows has been improved by this thesis. The work presented here has extended the known methods and accuracy issues of blood flow measurements in µPIV, improved the understanding of the blood velocity profile behavior, and applied that knowledge and methods to interesting, relevant problems in biomedical and biofluids engineering.
2
Karolyi, Daniel Roberts. « Hemodynamic wall shear stress in models of atherosclerotic plaques using phase contrast magnetic resonance velocimetry and computational fluid dynamics ». Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20132.
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3
Buchmann, Nicolas. « Development of Particle Image Velocimetry for In-Vitro Studies of Arterial Haemodynamics ». Thesis, University of Canterbury. Mechanical Engineering, 2010. http://hdl.handle.net/10092/4928.
Texte intégralRésumé :
Atherosclerosis and related cardiovascular diseases (CVDs) are amongst the largest causes of morbidity and mortality in the developed world, causing considerable monetary pressure on public health systems worldwide. Atherosclerosis is characterised by the build up of vascular plaque in medium and large arteries and is a direct precursor to acute vascular syndromes such a myocardial infarction, stroke or peripheral arterial diseases. The causative factors leading to CVD still remain relatively poorly understood, but are becoming increasingly identifiable as a dysfunction of the endothelial cells that line the arterial wall. It is well known that the endothelium responds to the prevailing fluid mechanic (i.e. haemodynamic) environment, which plays a crucial role in the localised occurrence of atherosclerosis near vessel bends and bifurcations. In these areas, disturbed haemodynamics lead to flow separation and very low wall shear stress (WSS), which directly affects the functionality of the endothelium and impedes the transport of important blood borne agonists and antagonists.
Detailed full field measurements assessing complex haemodynamics are sparse and consequently this thesis aims to address some of the important questions related to arterial haemodynamics and CVD by performing in-vitro flow measurements in physiologically relevant conditions. In particular, this research develops and uses state-of-the-art Particle Image Velocimetry (PIV) techniques to measure three-dimensional velocity and WSS fields in scaled models of the human carotid artery. For this purpose, the necessary theoretical and experimental concepts are developed and in-depth analyses of the underlying factors affecting the local haemodynamics and their relation to CVD are carried out.
In the first part, a methodology for the construct of transparent hydraulic flow phantoms from medical imaging data is developed. The arterial geometries are reproduced in optically clear silicone and the flowing blood is modelled with a refractive index matched blood analogue. Subsequently, planar and Stereo-PIV techniques are developed and verified. A novel interfacial PIV (iPIV) technique is introduced to directly measure WSS by inferring the velocity gradient from the recorded particle images. The new technique offers a maximal achievable resolution of 1 pixel and therefore removes the resolution limit near the wall usually associated with PIV. Furthermore, the iPIV performance is assessed on a number of numerical and experimental test cases and iPIV offers a significantly improved measurement accuracy compared to more traditional techniques.
Subsequently, the developed methodologies are applied in three studies to characterise the velocity and WSS fields in the human carotid artery under a number of physiological and experimental conditions. The first study focuses on idealised vessel geometries with and without disease and establishes a general understanding of the haemodynamic environment.
Secondly, a physiological accurate vessel geometry under pulsatile flow conditions is investigated to provide a more realistic representation of the true in-vivo flow conditions. The prevailing flow structure in both cases is characterised by flow separation, strong secondary flows and large spatial and temporal variations in WSS. Large spatial and temporal differences exist between the different geometries and flow conditions; spatial variations appear to be more significant than transient events.
Thirdly, the three-dimensional flow structure in the physiological carotid artery model is investigated by means of stereoscopic and tomographic PIV, permitting for the first time the measurement of the full 3D-3C velocity field and shear stress tensor in such geometries. The flow field within the model is complex and three-dimensional and inherently determined by the vessel geometry and the build up of an adverse pressure gradient. The main features include strong heliocoidal flow motions and large spatial variations in WSS.
Lastly, the physiological implications of the current results are discussed in detail and reference to previous work is given.
In summary, the present research develops a novel and versatile PIV methodology for haemodynamic in vitro studies and the functionality and accuracy is demonstrated through a number of physiological relevant flow measurements.
4
Jun, Brian H. « In vitro micro particle image velocimetry measurements in the hinge region of a bileaflet mechanical heart valve ». Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53380.
Texte intégralRésumé :
A number of clinical, in vitro and computational studies have shown the potential for thromboembolic complications in bileaflet mechanical heart valves (BMHV), primarily due to the complex and unsteady flows in the valve hinges. These studies have focused on quantitative and qualitative parameters such as velocity magnitude, turbulent shear stresses, vortex formation and platelet activation to identify potential for blood damage. However, experimental characterization of the whole flow fields within the valve hinges has not yet been conducted. This information can be utilized to investigate instantaneous damage to blood elements and also to validate numerical studies focusing on the hinge’s complex fluid dynamics. The objective of this study was therefore to develop a high-resolution imaging system to characterize the flow fields and global velocity maps in a BMHV hinge. Subsequently, the present study investigated the effect of hinge gap width on flow fields in a St. Jude Medical BMHV. The results from this study suggest that the BMHV hinge design is a delicate balance between reduction of fluid shear stresses and areas of flow stasis during leakage flow, and needs to be optimized to ensure minimal thromboembolic complications. Overall, the current study demonstrates the ability of high-resolution Micro Particle Image Velocimetry to assess the fluid flow fields within the hinges of bileaflet mechanical heart valves, which can be extended to investigate micro-scale flow domains in critical regions of other cardiovascular devices to assess their blood damage potential.
5
Gliah, Omemah Rajab. « In Vitro Investigation of Cell-Free Layer Formation in Microchannels : Dependency on the Red Blood Cell Aggregation and Field of Shear ». Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37211.
Texte intégralRésumé :
Red blood cells (RBCs) form approximately 40 to 45% of the human blood volume, and their behaviour and characteristics are the main determinant of blood properties, such as viscosity. RBCs are deformable species and stack together under low shear rate to form aggregates or rouleaux. Flowing RBCs migrate away from the wall leaving a cell-depleted layer known as the cell-free layer (CFL). This layer contributes to the blood viscosity and exchange between the RBCs and the target cells: a thinner CFL enhances the exchange process by reducing the diffusion distance. The formation of this CFL, however, is not yet completely understood.
The goal of this study is to improve the understanding of the formation of the CFL in the micro-flow. This was accomplished by studying the effects of changing both the flow rate and the microchannel geometry on blood flow in microchannels.
In this work, 10% hematocrit human blood suspensions were prepared in native plasma and flowed through poly-dimethylsiloxane (PDMS) microchannels of 100 μm x 34 μm cross-section. Investigation of the flowing cells was performed by using micro particle image velocimetry (μPIV) coupled with a high-speed camera. First, the high-speed camera images were processed with customized Matlab programs to detect and measure the CFL thickness and the RBC aggregates sizes. Second, the blood flow velocity profiles were measured using μPIV in order to determine the actual flow rate, the RBCs’ centerline velocity, and the shear rate.
The results showed that the increase in both flow rate and shear rate significantly reduced the CFL thickness and RBC aggregates size. Comparison of the upstream and downstream measurements in the bifurcating microchannel showed that the change in microchannel geometry did not significantly influence CFL thickness and RBC aggregate size, while within the daughter branches, RBCs tended to flow close to the inner wall resulting in an undetectable CFL at the inner wall and in a larger CFL at the outer wall of the branch. These in vitro results quantitatively relate CFL thickness and RBC aggregate size at different shear rates. The findings are of immediate interest regarding the understanding of microcirculation and improved designs of microchips.
6
Ziegenhein, Thomas, et Dirk Lucas. « On sampling bias in multiphase flows : Particle image velocimetry in bubbly flows ». Helmholtz-Zentrum Dresden - Rossendorf, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-197551.
Texte intégralRésumé :
Measuring the liquid velocity and turbulence parameters in multiphase flows is a challenging task. In general, measurements based on optical methods are hindered by the presence of the gas phase. In the present work, it is shown that this leads to a sampling bias. Here, particle image velocimetry (PIV) is used to measure the liquid velocity and turbulence in a bubble column for different gas volume flow rates. As a result, passing bubbles lead to a significant sampling bias, which is evaluated by the mean liquid velocity and Reynolds stress tensor components. To overcome the sampling bias a window averaging procedure that waits a time depending on the locally distributed velocity information (hold processor) is derived. The procedure is demonstrated for an analytical test function. The PIV results obtained with the hold processor are reasonable for all values. By using the new procedure, reliable liquid velocity measurements in bubbly flows, which are vitally needed for CFD validation and modeling, are possible. In addition, the findings are general and can be applied to other flow situations and measuring techniques.
7
Faure, M. A. « Particle image velocimetry measurement of in-cylinder flows ». Thesis, University of Brighton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387818.
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Jessen, Wilhelm. « Particle image velocimetry measurements of film cooling flows / ». Aachen : Mainz, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017075640&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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9
Brady, Michael Richard. « Subpixel Resolution Schemes for Multiphase Flows ». Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36104.
Texte intégralRésumé :
This effort explores novel sub-resolution particle center estimation algorithms for Digital Particle Tracking Velocimetry (DPIV). The errors of these new methods were classified through Monte-Carlo simulations. These schemes provide direct measurements of the apparent particle image diameter and the subpixel position. The new methods significantly reduce the bias error due to pixel discretization, thus reducing the total error in the position and sizing measurement compared to the classic three point and least squares Gaussian estimators. In addition, the accuracy of the least-squares fits were essentially independent of the true particle diameter and significantly reduced the particle position error compared with current estimation schemes. The results of the Monte Carlo simulations were validated in a high pressure spray atomization experiment.Master of Science
10
Fratantonio, Dominique. « Molecular tagging velocimetry in rarefied and confined gas flows ». Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0027.
Texte intégralRésumé :
Le marquage moléculaire est une technique expérimentale permettant d’effectuer de manière peu intrusive de la vélocimétrie au sein des écoulements. La mesure est basée sur le suivi de molécules capable d’émettre de la lumière suite à une excitation par une source laser. La mesure locale de vitesse est alors déduite de la visualisation du déplacement des molécules traceuses. Bien que la vélocimétrie par marquage moléculaire (MTV) ait déjà été utilisée avec succès pour des écoulements liquides ou gazeux, son application à des écoulements gazeux raréfiés internes reste encore un défi en raison de la diffusion moléculaire élevée et de la faiblesse de l’émission lumineuse à basse pression. Néanmoins, pouvoir appliquer la MTV en condition de gaz raréfié est intéressant du fait du manque de données expérimentales locales nécessaires à une meilleure compréhension des mécanismes d’interaction moléculaire entre le gaz et une surface solide. Dans ce travail, une étude expérimentale a été menée sur l’intensité et le temps de vie de la photoluminescence des traceurs moléculaires utilisés, à savoir l’acétone et le diacétyle vapeurs. Cette analyse a permis d’estimer les conditions expérimentales optimales pour l’application de la MTV aux gaz raréfiés. Ainsi, la MTV a été appliquée à des écoulements de mélanges gaz-traceur à basses pressions dans un canal millimétrique de section rectangulaire, fournissant ainsi les premiers résultats de vélocimétrie en régime d’écoulement légèrement raréfiéMolecular tagging velocimetry (MTV) is an optic experimental technique widely employed for measuring the velocity field in fluid flows. The measuring principle is based on the tracking of molecules able to emit light in response to a laser excitation. By seeding the flow with this tracer, local velocity measurements can be carried out by following the displacement of the emitting molecules. While this technique has already been successfully applied in liquid and gas flows, the application to rarefied and confined gas flows is still a challenge due to the high molecular diffusion and the low emitted light from the tracer at low pressures. The interest in applying MTV in rarefied conditions derives from the absence of local experimental data that can allow a better understanding on the mechanisms of interaction between the gas molecules and the wall surface. In this work, an experimental analysis of the intensity and lifetime of the photoluminescence of the molecular tracers employed, i.e., acetone and diacetyl, is presented. This analysis allowed to estimate the best working conditions in order to be able to apply MTV to rarefied gas flows. Thus, MTV has been applied to gas-tracer mixtures at low pressures in a millimetric rectangular channel producing the first preliminary results in the slip flow regime
11
Moseley, Rhodri Pierre. « The application of particle image velocimetry to wing vortex flows ». Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392196.
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Lawson, Nicholas J. « The application of particle image velocimetry to high speed flows ». Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/11366.
Texte intégralRésumé :
Particle Image Velocity (PIV) is now a well established, non-intrusive technique for the two dimensional measurement of fluid velocity from a single plane of interest within a fluid flow. This thesis presents new work into the application of the double pulsed PIV technique to highspeed flows. The areas of work can be split into three major areas. The first area of work involved a comprehensive study into data reduction using autocorrelation. Results from the study allowed the development of an optimisation method which provides a consistent basis for experimental design. Further work validated this method by comparing equivalent results from sets of PIV transparencies processed using a system developed from commercially available image processing equipment. The second area of work involved supersonic flow studies of a de Laval expansion nozzle. PIV results were recorded from both inside and outside the nozzle. Inside the nozzle the PIV results resolved a normal shock and allowed comparisons with a 1D theoretical model, a CFD prediction and Schlieren photographs. Outside the nozzle the PIV data permitted overexpanded jet shock cell structures to be resolved and compared to a shock cell model. The final area of work involved development of an image labelling system for high speed flows by changing the transfer characteristics of the recording optics between exposures. A general theory of this technique was developed and a system designed and tested which can be applied to flows of arbitrarily high speed.
13
Li, Kejian. « Blood flows in arterial models ». Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239068.
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Cadel, Daniel R. « Advanced Instrumentation and Measurements Techniques for Near Surface Flows ». Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/72968.
Texte intégralRésumé :
The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full scale conditions in laboratory experiments, and advanced diagnostics become valuable in providing data not available from traditional means. A new variant of Doppler global velocimetry (DGV) known as cross-correlation DGV is developed to measure boundary layer profiles on a wind turbine blade airfoil in the large scale Virginia Tech Stability Wind Tunnel. The instrument provides mean velocity vectors with reduced sensitivity to external conditions, a velocity measurement range from 0ms^-1 to over 3000ms^-1, and an absolute uncertainty. Monte Carlo simulations with synthetic signals reveal that the processing routine approaches the Cramér-Rao lower bound in optimized conditions. A custom probe-beam technique is implanted to eliminate laser flare for measuring boundary layer profiles on a DU96-W-180 wind turbine airfoil model. Agreement is seen with laser Doppler velocimetry data within the uncertainty estimated for the DGV profile.
Lessons learned from the near-wall flow diagnostics development were applied to a novel benchmark model problem incorporating the relevant physical mechanisms of the high amplitude periodic turbulent flow experienced by turbine blades in the field. The model problem is developed for experimentally motivated computational model development. A circular cylinder generates a periodic turbulent wake, in which a NACA 63215b airfoil with a chord Reynolds number Re_c = 170, 000 is embedded for a reduced frequency k = (pi)fc/V = 1.53. Measurements are performed with particle image velocimetry on the airfoil suction side and in highly magnified planes within the boundary layer. Outside of the viscous region, the Reynolds stress profile is consistent with the prediction of Rapid Distortion Theory (RDT), confirming that the redistribution of normal stresses is an inviscid effect. The fluctuating component of the phase- averaged turbulent boundary layer profiles is described using the exact solution to laminar Stokes flow. A phase lag similar to that in laminar flow is observed with an additional constant phase layer in the buffer region. The phase lag is relevant for modeling the intermittent transition and separation expected at full scale.Ph. D.
15
Ertürk, Düzgün Nihal. « Particle image velocimetry applications in complex flow systems ». Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/83517.
Texte intégralRésumé :
El objetivo principal de esta tesis es la mejora y la aplicación de la técnica PIV para analizar diferentes flujos de fluidos complejos en los sistemas que contienen partes sólidos móviles o estacionarias. Las partículas de alginato con/sin compuesto de fluoresceína incrustada se han desarrollado como una serie de elementos alternativos de siembra de nuevas aplicaciones de flujo para el PIV. Se ha encontrado que las micro-partículas de alginato tienen muchas ventajas sobre los tradicionales utilizados en sistemas de PIV. Un estudio amplio sobre el análisis del flujo en tres dimensiones de la bomba de engranajes externa se ha hecho por la técnica tiempo-resuelva PIV para investigar la dinámica y las estadísticas de flujo turbulento. Vorticidad y zonas turbulentas de alta energía cinética se han identificado dentro de la bomba de engranajes externa. La técnica PIV se ha aplicado de manera eficiente para analizar un intercambiador de calor de motor de flujo de bypass en un túnel del viento de bajo velocidad. Las partículas de alginato que contienen fluoresceína se han utilizado eficientemente en los experimentos que conducen a mejorar la calidad de la imagen PIV y analizar las estructuras de pequeña escala de los flujos.The main objective of the thesis is the improvement and application of the PIV technique to analyse different complex fluid flows in systems that contain solid moving or stationary parts. The alginate particles with/without fluorescein compound imbedded have been developed as a new alternative flow seeding elements for PIV applications. It has been found that the alginate micro particles have many advantages over traditional ones used in PIV systems. A comprehensive study on the three-dimensional flow analysis of the external gear pump has been done by time-resolved PIV technique to investigate its turbulent flow dynamics and statistics. Vorticity and high turbulent kinetic energy areas have been identified inside the external gear pump. The PIV technique has been efficiently applied to analyse an engine bypass flow heat exchanger in a low speed wind tunnel. The alginate particles containing fluorescein have been efficiently used in the experiments that lead to improve the PIV image quality and analyse the small-scale structures of the flows.
16
Yang, Ping. « Particle Vaporization Velocimetry and Quantitative Soot Concentration Measurement in Sooty Flows ». Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19843.
Texte intégralRésumé :
Soot is a combustion generated pollutant that is both a direct risk to human health and a contributing source to global environmental change. Soot can also be a controlling factor in heat transfer inside combustion systems. Thus there is a growing interest in being able to measure soot and understand its production in practical, turbulent combustion environments. Therefore, the specific objectives of this research work were: (1) developing a way to measure velocity of sooty regions that is compatible with existing methods for measuring temporally and spatially resolved soot concentration fields and (2) using these methods to make quantitative measurements of soot in an unsteady, turbulent-like combustor. The Particle Vaporization Velocimetry (PVV) technique was developed and is compatible with Laser Induced Incandescence (LII), a soot concentration measurement approach. PVV is a flow tagging approach, where a high intensity laser (~2-3 J/cm2) is used to vaporize a small region in the soot field. This approach was demonstrated to produce a long lasting and easily readable flow tag that allows for velocity measurements over a wide range of velocities. LII proved to be the best method for detection the motion of the tag after a fixed delay. PVV and LII were used to measure velocity and two-dimensional soot concentration fields in an acoustically excited burner. In addition, images of soot luminosity were obtained. Both laminar and transitional acetylene diffusion flames were studied. The results reveal that strong acoustic forcing can significantly reduce total flame soot, as well as maximum soot concentrations, while simultaneously increasing the average soot temperature. The influence of acoustically generated vortices on soot formation was studied, and soot and products mixture mostly likely dominant high soot concentration regions. Eventually, these mixtures will be propagated downstream and oxidized as a diffusion flame.
17
Koseli, Volkan. « Experimental And Theoretical Investigation Of Complex Flows By Ultrasound Doppler Velocimetry ». Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610727/index.pdf.
Texte intégralRésumé :
Non-invasive and fast flow measurement techniques have had increasing importance
for the last decades. Scientists are looking for such quick techniques to be able to
monitor real velocities without disturbing flow itself. Ultrasound Doppler
velocimetry (UDV) being one of such techniques promising with advantages of
getting simultaneous velocity measurements from several points and of applicability
for opaque liquids as well. UDV is a technique which is still being developed for
new applications and analysis of complex flows.
In this study effect of sinusoidal oscillating, turbulent (random) and viscoelastic fluid
motions on UDV signals were investigated theoretically and experimentally.
Obtained mathematical relations for random and viscoelastic motions were utilized
to get statistics of flow and distribution of relaxation spectrum, respectively.
Analytical analysis and numerical simulation of sinusoidal oscillating flow depicted
that there is a critical value for the ratio of oscillation amplitude to oscillation
frequency for a specified set of measurement parameters of UDV. Above this critical
value UDV is not successful to determine mean flow velocity. Mathematical
relations between velocity probability density function (PDF) &ndashvelocity auto correlation function (ACF) and UDV signal spectrum were obtained in the analysis v of flow with random velocity. Comparison of velocity ACFs from direct velocity measurements and from raw in-phase (I) and quadrature (Q) signals through derived relation, revealed that time resolution of UDV technique is not enough for getting a good velocity ACF and thus turbulence spectrum. Using I and Q signals rather than measured velocities to get velocity ACF, increased the time resolution in the order of number of pulses used for getting one velocity value (Nprn). Velocity PDF obtained from UDV spectrum was compared with the one obtained from measured velocities with the assumption of Gaussian PDF. Both velocity PDFs were consistent. Also some parameters of pipe turbulence from literature were compared with the presented findings from velocity ACF obtained from I and Q signals through derived relation. Results showed good compatibility. In the last part of the study, complex viscosity of a linear viscoelastic fluid mathematically related to spectrum of UDV for a pipe flow with small-amplitude oscillating pressure field. Generalized Maxwell model was employed to express complex viscosity terms. Zero frequency (mean flow) component of UDV spectrum was used to obtain an equation for relaxation viscosities of generalized Maxwell model. Results have revealed that UDV technique can also be used to probe some of viscoelastic material functions. In conclusion, UDV is relatively new but a promising technique for the measurement and analysis of complex flows in a non-invasive manner.
18
Reeves, Mark. « Particle image velocimetry applied to internal combustion engine in-cylinder flows ». Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/7008.
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Particle Image Velocimetry (PIV) is now emerging as a powerful tool for the investigation of unsteady fluid mechanics. At the same time, the study and optimisation of in-cylinder flow processes in automotive Internal Combustion (IC) engines is of increasing importance in the design of improved combustion systems with lower emissions and favourable power and efficiency characteristics. This thesis describes the development and application of PIV as a routine diagnostic tool for the investigation of in-cylinder flows in a production geometry single cylinder research engine exhibiting "barrel swirl" or "tumbling" in-cylinder fluid motion. The work has involved the design and installation of a complete PIV engine facility, based around a four-valve, four-stroke Rover research engine equipped with piston crown optical access and a glass cylinder liner. Novel techniques for the on-line monitoring of important experimental parameters have been developed which permit the reliable acquisition of high spatial resolution PIV data from both horizontal and vertical measurement planes within the engine cylinder. A novel optical correction technique has been developed to control the severe particle image degradation which was experienced when imaging vertical planes within the glass cylinder. A simple means for selection of an appropriate corrective lens for this application is described, together with an experimental evaluation of the lens performance. A representative set of PIV images and data from both horizontal and vertical planes are then presented. These have been selected from a comprehensive set of flow mapping experiments in the motored engine. The data are discussed with reference to the work of others in engines of similar geometry and have shed new light on the detailed processes involved in the formation and breakdown of barrel swirl. Initial PIV measurements ahead of a flame under part load, skip fired conditions have also been made in the engine. This has demonstrated the possibility of investigating incylinder flow behaviour under conditions approaching those in a fully firing, production geometry optical engine. Finally, limitations in the PIV technique employed in this work and methods of overcoming them are described and the prospects for further work are discussed.
19
Chennaoui, Mourad. « Development of fluorescent tracers for velocimetry measurements in multiconstituent /multiphase flows ». Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/13368.
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This thesis describes the development of optimised fluorescent dye-doped tracer droplets for gas phase particle image Velocimetry (PIV), to study mixing in multi-phase flows. The use of these tracer droplets in applications where flare can be an obstacle to obtaining velocity flow data is also demonstrated. In PIV, micron-sized tracer particles are normally required to accurately follow the flow while in the same time providing optimum fluorescence signal for proper image capture. Thus, there is a requirement to identify dyes with high quantum yield that can be dissolved in suitable nebulisable solvents at high concentrations and to investigate the effect of high concentration on fluorescence properties, such as fluorescence concentration quenching effects that could lead to a decrease of the fluorescence signal from tracer droplets. The selection criteria of candidate dyes and the study of their fluorescence properties by steady-state spectrofluorometry are presented. Bis-MSB and DCM were identified to be the optimum blue and red emitting dyes and to offer high solubility in o-xylene and DMSO respectively. A novel experimental approach employing stabilised emulsions to emulate the fluorescence properties of micron-sized tracer droplets has been developed. The development of a single-colour-camera PIV system that can image micron-sized and spectrally distinct fluorescent tracers in a two-phase flow is reported. The use of dye-doped microemulsions in a novel micro-PIV seeding methodology for full field velocity measurements in microfluidic devices is presented. This approach gives improved particle image contrast and reduced motion parallax uncertainty, when compared to conventional solid seed particles. Results of micro-PIV measurements in T- and Y-junction microfluidic chips are presented. Channel velocity profiles were found to agree with CFD simulations.
20
Pendlebury, Jonathon Remy. « Light Field Imaging Applied to Reacting and Microscopic Flows ». BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5754.
Texte intégralRésumé :
Light field imaging, specifically synthetic aperture (SA) refocusing is a method used to combine images from an array of cameras to generate a single image with a narrow depth of field that can be positioned arbitrarily throughout the volume under investigation. Creating a stack of narrow depth of field images at varying locations generates a focal stack that can be used to find the location of objects in three dimensions. SA refocusing is particularly useful when reconstructing particle fields that are then used to determine the movement of the fluid they are entrained in, and it can also be used for shape reconstruction. This study applies SA refocusing to reacting flows and microscopic flows by performing shape reconstruction and 3D PIV on a flame, and 3D PIV on flow through a micro channel. The reacting flows in particular posed problems with the method. Reconstruction of the flame envelope was successful except for significant elongation in the optical axis caused by cameras viewing the flame from primarily one direction. 3D PIV on reacting flows suffered heavily from the index of refraction generated by the flame. The refocusing algorithm used assumed the particles were viewed through a constant refractive index (RI) and does not compensate for variations in the RI. This variation caused apparent motion in the particles that obscured their true locations making the 3D PIV prone to error. Microscopic PIV (µPIV) was performed on a channel containing a backward facing step. A microlens array was placed in the imaging section of the setup to capture a light field from the scene, which was then refocusing using SA refocusing. PIV on these volumes was compared to a CFD simulation on the same channel. Comparisons showed that error was most significant near the boundaries and the step of the channel. The axial velocity in particular had significant error near the step were the axial velocity was highest. Flow-wise velocity, though, appeared accurate with average flow-wise error approximately 20% throughout the channel volume.
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Thorpe, Steven J. « A study of Doppler global velocimetry in its application to aerodynamic flows ». Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365880.
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Kalpakli, Athanasia. « Experimental study of turbulent flows through pipe bends ». Licentiate thesis, KTH, Linné Flow Center, FLOW, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93316.
Texte intégralRésumé :
This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow. The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated. The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated. Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods. The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.QC 20120425
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Udrea, Doina Daciana. « High accuracy flow velocity measurements using particle image velocimetry : development and applications ». Thesis, University of Warwick, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300743.
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Freudenhammer, Daniel Kim [Verfasser], Cameron [Akademischer Betreuer] Tropea et Jürgen [Akademischer Betreuer] Hennig. « Magnetic Resonance Velocimetry for Unsteady Flows / Daniel Kim Freudenhammer ; Cameron Tropea, Jürgen Hennig ». Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1123729417/34.
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Clancy, Pamela S. « Development and application of three-component planar doppler velocimetry for high speed flows / ». The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948158625472.
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Dam, Charlotte Elgaard. « Particle image velocimetry, accuracy of the method with particular reference to turbulent flows / ». Thesis, University of Edinburgh, 1995. http://webex.lib.ed.ac.uk/homes/dam95.html.
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Yu, Xiaohong. « Hemodynamic analysis of blood flows in carotid bifurcations ». Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B3864700X.
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Yu, Xiaohong, et 于曉紅. « Hemodynamic analysis of blood flows in carotid bifurcations ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B3864700X.
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Abiven, Claude. « A Hybrid Dynamically Adaptive, Super-Spatio Temporal Resolution Digital Particle Image Velocimetry for Multi-Phase Flows ». Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34014.
Texte intégralRésumé :
A unique, super spatio-temporal resolution Digital Particle Image Velocimetry (DPIV) system with capability of resolving velocities in a multi-phase flow field, using a very sophisticated novel Dynamically Adaptive Hybrid velocity evaluation algorithm has been developed The unique methodology of this powerful system is presented, its specific distinctions are enlightened, confirming its flexibility, and its superior performance is established by comparing it to the most established best DPIV software implementations currently available. Taking advantage of the most recent advances in imaging technology coupled with state of the art image processing tools, high-performing validation schemes including neural networks, as well as a hybrid digital particle tracking velocimeter (DPTV), the foundation for a unique system was developed. The presented software enables one to effectively resolve tremendously demanding flow-fields. The resolution of challenging test cases including high speed cavitating underwater projectiles as well as high pressure spray demonstrate the power of the developed device.Master of Science
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Zhou, Mingyong. « Particle image velocimetry applied to non-reacting and reacting flows within cylindrical combustion chambers ». Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/12195.
Texte intégralRésumé :
Particle Image Velocimetry (PlY) is a technique for measuring instantaneous twodimensional fluid velocity fields from a chosen plane of interest within a flow field. This thesis presents new developments and applications of the technique which have been used to study both the non-reacting and reacting flow fields within cylindrical combustion chambers. Non-reacting, swirling laminar flow fields near the transitional flow regime have been investigated by both Computational Fluid Dynamics (CFD) modelling and PIV experiments. Direct comparisons between CFD, PlY and other published results are made and close agreements are found. Additionally, the PlY technique has been optimised by careful use of a thin laser illumination sheet and correct choice of laser pulse separation. This has enabled successful PlY measurements in the boundary layers of the flow field where high velocity gradients exist. The PlY technique has been applied to measure the flame development and propagation process within the chamber under both quiescent and swirling flow conditions. Representative sequences of PIV results at different flame propagation stages are obtained and the accuracy in the extraction of the flame location is discussed. They clearly reveal the instantaneous flame front position and the unburned gas velocity field simultaneously. These features provide further insight into the combustion process itself and also the interaction between the combustion and flow field. A new application of PIV, combined with a flame speed detection technique, has been proposed and developed to obtain direct measurements of the laminar burning velocity of combustible mixtures. The laminar burning velocity is determined as the difference between the flame speed and the unburned gas velocity immediately ahead of the flame front. PIV is used to measure the unburned gas velocity field and either a pair of ionisation probes or a laser beam refraction technique is used to measure the local flame speed simultaneously. The relative merits of each technique are compared. The laminar burning velocities of propane-air mixtures initially at atmospheric conditions for equivalence ratios ranging from 0.7 - 1.4 were measured. The measured values show close agreement with previously published results based on other techniques. The advantages and limitations of the PIV techniques used in this work are examined and the prospects of their improvement and further application are discussed.
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Khan, Firoz R. « Investigation of turbulent flows and instabilities in a stirred vessel using particle image velocimetry ». Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/14171.
Texte intégralRésumé :
Extensive use of stirred vessels in the process industries for various operations has attracted researchers to study the mixing mechanisms and its effects on the processes. Among the various flow-measuring methods, Particle Image Velocimetry (PlV) technique has become more popular in comparison to LDA and HW A methods because of its ability to provide instantaneous velocity fields. The present study uses this technique to investigate the flowfields and turbulent properties in a 290mm vessel stirred by Rushton Disc turbine (RDT) and Pitched blade turbine (PBT) impellers. Angle-resolved instantaneous flow-fields were obtained using 2-D and 3-D PlV technique. Flows in the RDT were examined. The distribution of out-of-plane vorticity and turbulent properties such as rms velocities, Reynolds stresses and turbulent kinetic energy was discussed. The flow number and power number of the RDT impeller were obtained as 0.83 and 5.16 respectively. Flows generated by the PBT impeller were examined in more detail. For this purpose, a multiblock approach was developed which allowed analysing larger fields of view with reasonably higher resolution. Whole vessel was thus mapped and various turbulent properties were examined. The mean flow-fields, out-of-plane vorticity and turbulent properties such as Reynolds stresses, turbulent kinetic energy and turbulent energy dissipation rates were estimated at different angle of blade rotation. The variation of the trailing vortex axis was obtained. The pumping number and power number ofPBT impeller was obtained as 0.86 and 1.52 respectively. Using this information, an integral length scales were estimated using 2-D FFT autocorrelation, which showed that these length scales vary significantly through out the vessel. It is demonstrated that assuming constant length scale through out the vessel could underestimate dissipation rate up to 25% in the impeller discharge. A kinetic energy balance was carried out around the PBT blades. It is shown that around 44% of the total power consumed by the impeller is dissipated within the impeller. The average rate of dissipation of kinetic energy was 39 times higher in the impeller region than the average dissipation rate in the vessel. Using LDA and PIV techniques, macro-instabilities (Ml) were studied. Spectral analysis was done using LOMB algorithm, which showed the presence of a dimensionless frequency of O.013-0.0174N in the RDT and PBT impellers. The frequency of Ml varied linearly with the impeller speed. The maximum broadening of turbulence levels due to the presence of Ml was around 20% for the PBT and 18% for the RDT impeller. The effect of mixing on the feed locations was studied using PlV measurements. Results showed that there is no direct effect of feed coming out of the feed pipe on the flow distribution, however, due to feed pipe, there was a wake formation close to the feed pipe. The low Reynolds number in the wake can affect local mixing conditions close to the feed pipe. At the end, angle-resolved Reynolds stresses were calculated and was noticed that flows in the vessel were isotropic in the bulk of the vessel however, anisotropic flow was noticed in the impeller stream.
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Raben, Samuel. « Near wall high resolution particle image velocimetry and data reconstruction for high speed flows ». Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/32653.
Texte intégralRésumé :
The aim of this work was to understand the physical requirements as well as to develop methodology required to employ Time Resolved Digital Particle Image Velocimetry (TRDPIV) for measuring high speed, high magnification, near wall flow fields. Previous attempts to perform measurements such as this have been unsuccessful because of both limitations in equipment as well as proper methodology for processing of the data. This work addresses those issues and successfully demonstrates a test inside of a transonic turbine cascade as well as a high speed high magnification wall jet.
From previous studies it was established that flow tracer delivery is not a trivial task in a high speed high back pressure environment. Any TRDPIV measurement requires uniform spatial seeding density, but time-resolved measurements require uniform temporal seeding density as well. To this end, a high pressure particle generator was developed. This advancement enhanced current capability beyond what was previously attainable. Unfortunately, this was not sufficient to resolve the issue of seeding all together, and an advanced data reconstruction methodology was developed to reconstruct areas of the flow field that where lost do to inhomogeneous seeding. This reconstruction methodology, based on Proper Orthogonal Decomposition (POD), has been shown to produce errors in corrected velocities below tradition spatial techniques alone. The combination of both particle generator and reconstruction methodology was instrumental for successfully acquiring TRDPIV measurements in a high speed high pressure environment such as a transonic wind tunnel facility.
This work also investigates the development of a turbulent wall jet. This experiment helped in demonstrating the capability of taking high speed high magnification TRDPIV measurements. This experiment was very unique in that it is one of only a few experiments that studied the developing region of these jets. The Reynolds number ranged for this experiment from 150 â 10,000 which corresponded to velocities of 1 - 80 m/s. The results from this experiment showed good agreement with currently published time averaged data. Using scaling laws for fully developed jets a new scaling law was found for the developing region of the jet that could be applied to all Reynolds numbers in this study. A temporal investigation was also carried out using the temporal coefficients from POD. A vortex identification scheme was also applied to all of the Reynolds numbers showing clear trends as Reynolds number increased.Master of Science
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Cardwell, Nicholas Don. « Investigation of Particle Trajectories for Wall Bounded Turbulent Two-Phase Flows ». Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/29642.
Texte intégralRésumé :
The analysis of turbulent flows provides a unique scientific challenge whose solution remains central to unraveling the fundamental nature of all fluid dynamics. Measuring and predicting turbulent flows becomes even more difficult when considering a two-phase flow, which is a commonly encountered engineering problem across many disciplines. One such example, the ingestion of foreign debris into a gas turbine engine, provided the impetus for this study. Despite more than 40 years of research, operation with a particle-laden inlet flow remains a significant problem for modern turbomachines. The purpose, therefore, is to develop experimental methods for investigating multi-phase flows relevant to the cooling of gas turbine components.
Initially, several generic components representing turbine cooling designs were evaluated with a particle-laden flow using a special high temperature test facility. The results of this investigation revealed that blockage was highly sensitive to the carrier flowfield as defined by the cooling geometry. A second group of experiments were conducted in one commonly used cooling design using a Time Resolved Digital Particle Image Velocimetry (TRDPIV) system that directly investigated both the carrier flowfield and particle trajectories. Traditional PIV processing algorithms, however, were unable to resolve the particle motions of the two-phase flow with sufficient fidelity. To address this issue, a new Particle Tracking Velocimetry (PTV) algorithm was developed and validated for both single-phase and two-phase flows. The newly developed PTV algorithm was shown to outperform other published algorithms as well as possessing a unique ability to handle particle laden two-phase flows.
Overall, this work demonstrates several experimental methods that are well suited for the investigation of wall-bounded turbulent two-phase flows, with a special emphasis on a turbine cooling method. The studies contained herein provide valuable information regarding the previously unknown fluid and particle dynamics within the turbine cooling system.Ph. D.
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Houriez--Gombaud-Saintonge, Sophia. « Analyse automatisée des données 3D+t d’imagerie par résonance magnétique de vélocimétrie. Quantification de l’apport du 3D+t ». Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS328.
Texte intégralRésumé :
Les maladies cardiovasculaires sont la première cause de mortalité dans les pays de l’OCDE du fait notamment du vieillissement global de la population, faisant d’elles l’un des enjeux majeurs de santé à l’échelle mondiale. Les progrès de l’imagerie permettent aujourd’hui de mieux comprendre et diagnostiquer ces maladies de manière non-invasive. Plus récemment, une technique novatrice d’imagerie non-invasive et non-irradiante appelée « IRM de flux 4D » permet pour la première fois d’imager la vitesse du flux sanguin en 3 dimensions pendant tout un cycle cardiaque, offrant ainsi de nouvelles perspectives de visualisation, de compréhension et de mesure. Cette thèse en traitement d’images, réalisée en lien avec des cardiologues et radiologues a pour objectif de développer de nouveaux indicateurs, pour quantifier l’apport de l’IRM de flux 4D notamment dans :1) l’évaluation de la rigidité aortique où une comparaison de méthodes pour l’évaluation de la vitesse de l’onde de pouls a été réalisée 2) l’analyse de la désorganisation de flux dans la dilatation aortique physiologique (âge) et pathologique ; 3) l’évaluation des flux de remplissage cardiaquesCardiovascular diseases remain the leading cause of death in OECD countries, in particular, because of the population aging, making it one of the major health issues on a global scale. Advances in imaging today make it possible to better understand and diagnose these diseases in a non-invasive way. More recently, a new non-invasive and non-radiative imaging technique named « 4D Flow MRI » allows for the first time to image the speed of blood flow in three dimensions during a whole cardiac cycle, thus offering new perspectives of visualization, understanding, and measurement. This thesis in image processing carried out in connection with cardiologists and radiologists aims to develop new indicators and to quantify the contribution of 4D flow MRI especially in 1) the assessment of the aortic stiffness leading to a comparison between several approaches to estimate the pulse wave velocity 2) the analysis of flow disorganization in aging and pathological dilation 3) the evaluation of filling flow in the left ventricle
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Veale, William. « Shallow flow turbulence : an experimental study ». Thesis, University of Canterbury. Civil Engineering, 2005. http://hdl.handle.net/10092/1073.
Texte intégralRésumé :
A particle tracking velocimetry (PTV) system is used to investigate the turbulent properties at the free surface of shallow shear flows and a shallow vortex street (VS) wake flow. The resolution of the PTV system enables information to be gathered regarding the large-scale turbulent structure of these flows, and also enables analysis to proceed in both the temporal and spatial domains. Statistical tools such as the probability density function (PDF), autocorrelation and power spectral density (PSD) are utilised to characterise the turbulent properties at the flow surface. Two supercritical flows and one subcritical shallow shear flow are analysed. Taylor's frozen turbulence hypothesis is shown to be valid for these flows, and the integral length scales indicate that 2D isotropic structures with scales larger than the flow depth are present at the free surface. Such large-scale structures at the free surface are consistent with observations from dye visualisation experiments and with "spiral eddies" identified by Kumar, et al (1998). The longitudinal extent of near and intermediate wake fields for the shallow VS wake flow is well defined by the integral wake length scale specified by v.Carmer (2005). The near wake region is characterised by high rates of exchange between the mean flow and large-scale 2D coherent structures (2DCS). In the intermediate field, the rate of decay of the turbulent stress components greatly diminishes as the 2DCS are stabilised and dissipated under the action of bed friction. Multiple peaks are observed in the power spectral density of the turbulent fluctuations. The periodic shedding of 2DCS behind the circular cylinder is characterised by an energy peak at a Strouhal number of 0.21, and further energy peaks are observed in the near-wake region. The PSD estimates are consistent with the findings of v.Carmer (2005) in which a -5/3 decay law to high frequencies is observed, and no evidence of an inverse energy cascade is present.
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Le, Andy Vinh. « Blood Microflow Characterization Using Micro-Particle Image Velocimetry and 2-Beam Fluorescence Cross-Correlation Spectroscopy ». Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41535.
Texte intégralRésumé :
Blood flow through microcirculation in both simple and complex geometry has been difficult to predict due to the composition and complex behavior of blood at the microscale. Blood is a dense suspension of deformable red blood cells that is comparable in dimensions to the microchannels that it flows through. As a result, rheological properties at the microscale can vastly differ from bulk rheological properties due to non-continuum effects. To further develop our understanding of blood microflow; experimental techniques should be explored.
In this work, we explore micro-particle image velocimetry (μPIV) and two-beam fluorescence cross-correlation spectroscopy (2bFCCS) in the application of characterizing blood in microflow conditions. For the development of the μPIV analysis, a polydimethylsiloxane co-flow channel is used to observe blood flow in controlled conditions. Flow conditions (velocity profile and blood layer thickness) are selected based on an analytical model and compared to experimental measurement. The experimental results presented indicate that current flow conditions are inadequate in providing a controlled rate of shear on the blood layer in the co-flow channel and further optimization are required to improve the measurement of the velocity profile. For the development of the 2bFCCS application for blood flow analysis, a wide glass capillary microfluidic device is used to complete the verification of fluorescence fluid admissibility, the effect of laser intensity on inducing photobleaching and the velocity measurement performance. The experimental measurement of the velocity profile is validated against the theoretical profile for a rectangular channel. Results of the velocity profile of high concentration red blood cells show promise in the technique’s ability to measure blood microflows closer to physiological conditions.
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Lee, Wing Kai. « The application of 2D and 3D particle image velocimetry (PIV) for measurement in high speed flows ». Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343141.
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Sabo, Kevin (Kevin M. ). « Development of a two-dimensional model of blood microcirculation flows ». Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112477.
Texte intégralRésumé :
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 173-174).
This thesis presents the development of a dimensionless blood microcirculation model for the study of blood microcirculation flows. It is a two dimensional, axially symmetric, incompressible, Newtonian-flow, Krogh cylinder model subjected to axially periodic boundary conditions. This model formulation allows for the use of the streamfunction-vorticity formulation of the Navier-Stokes equation, which offers simplification to boundary conditions and also allows for the use of a non-uniform, collocated mesh. A streamfunction vorticity formulation of the Immersed Boundary Method is also developed, specifically for the boundary conditions along the immersed boundary (red blood cell membrane). Periodic boundary conditions are used, with the assumption of fully-developed flow, in order to focus on the effects of the transient diffusion of oxygen into the surrounding tissue, orthogonal to the capillary flow direction.
by Kevin Sabo.
S.M.
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Barber, Jared Oliver. « Computational Simulation of Red Blood Cell Motion in Microvascular Flows ». Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193887.
Texte intégralRésumé :
Microvascular transport is strongly influenced by the nonuniform partitioning of red blood cells at diverging microvessel bifurcations, where blood flows from one mother vessel into two daughter vessels. In such bifurcations, the volume fractions of red blood cells in the blood entering each daughter vessel typically differ significantly from the volume fraction in the mother vessel. This phenomenon is caused, to a first approximation, by nonuniform distribution of red blood cells in the cross-section of the mother vessel and the tendency of red blood cells to follow background fluid streamlines. In smaller vessels, however, red blood cell trajectories can deviate significantly from fluid streamlines. In this dissertation, the mechanical reasons for these deviations and their contributions to nonuniform partitioning are analyzed.A two-dimensional model is used to simulate the motion and deformation of flexible particles as they travel alone through a diverging microvessel bifurcation. Deviations of particle trajectories from background fluid streamlines result from migration towards the mother vessel centerline upstream of the bifurcation and flow perturbations caused by cell obstruction in the bifurcation region. Cell migration, which arises because of flexibility, causes more nonuniform partitioning while cell obstruction causes more uniform partitioning. Bifurcations with differently sized daughter vessels experience, on average, a higher red blood cell flux into the smaller branch. Partitioning is unaffected by daughter branching angles.The motion of two interacting cells is also considered. In diverging bifurcations several types of interactions were found, in which the presence of a nearby cell causes a cell to enter a different branch than it would have otherwise. The net effect of these interactions is to cause more uniform partitioning. In wall-bounded linear shear flow, a two-dimensional swapping interaction was identified, in which two cells on different background fluid streamlines approach each other, slowly move onto their partner's streamline, and then move away from each other.The simulations produced by this two-dimensional model provide insight into the effects of red blood cell deformability, bifurcation geometry and volume fraction of red blood cells on red blood cell partitioning and on the resultant distribution and transport of materials in the microvasculature.
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Kähler, Christian. « The significance of coherent flow structures for the turbulent mixing in wall-bounded flows ». Köln : DLR, Dt. Zentrum für Luft- und Raumfahrt, 2004. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=015380581&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Stapleton, Brian J. « An investigation of in-cylinder flows in a direct injection compression ignition engine using particle image velocimetry ». Thesis, Loughborough University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529505.
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Förster, Felix Johannes [Verfasser]. « Laser-Induced Thermal Acoustics : Simultaneous Velocimetry and Thermometry for the Study of Compressible Flows / Felix Johannes Förster ». München : Verlag Dr. Hut, 2017. http://d-nb.info/1126297690/34.
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Vasilevskiy, Oleksandr. « Flux maximizing geometric flows for 2D and 3D blood vessel segmentation ». Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33070.
Texte intégralRésumé :
The visualization of two-dimensional and three-dimensional vascular structures is of significant interest in image-guided surgery. This assists clinicians in pre-operation planning, real-time operating room decision making, and post-operation monitoring. In order to achieve this goal, vascular networks must first be segmented from intensity data such as CT or MR angiography images. A framework for addressing this problem is the use of geometric flows where a curve (in two dimensions) or a surface (in three dimensions) is evolved under constraints from image forces so that it clings to features of interest in an intensity image. Recent variations on this theme take into account properties of enclosed regions and textures and allow for multiple curves or surfaces to be simultaneously represented. However, it is not clear how to apply these techniques to images of low contrast elongated structures, such as blood vessels. To address this problem we derive the gradient flow which maximizes the rate of increase of flux of an auxiliary vector field through a curve or surface. The calculation leads to a simple and elegant interpretation which is essentially parameter free. We illustrate its advantages with level-set based segmentations of 2D and 3D angiography images of blood vessels.
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Cole, Jonathan Samuel. « Pulsatile, non-Newtonian blood flows through typical arterial bypass graft models ». Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326405.
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Nguyen, Quang Duy. « Numerical and Experimental Investigations of Flows over Confined Circular Cylinders ». Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29401.
Texte intégralRésumé :
This study is concerned with flows past confined circular cylinders symmetrically positioned between two parallel plates over a wide range of blockage ratios (β) and Reynolds numbers (Re). Such flow configuration is highly relevant to engineering applications such as for mixing and heat transfer enhancement. Although previous studies have examined the effects of confinement on the flow behaviour and hydrodynamic properties of circular cylinders, there exists a clear knowledge gap in terms of the lift and drag coefficients and the Strouhal number of the confined cylinder at moderate blockage ratios (β ≤ 0.5). Further, the role of the separated shear layers on wake dynamics at high blockage ratios is not well understood. The purpose of the present study is to obtain fundamental understandings of the hydrodynamic characteristics, the wake dynamics and the role of the separated shear layers in the confined flows. The thesis covers two major investigations of a confined circular cylinder at moderate blockage ratios and at a high blockage ratio respectively, and both numerical simulation and experimental measurement are adopted in this project.
The first investigation is concerned with the hydrodynamic properties and wake dynamics of a confined circular cylinder at blockage ratios between 1/6 and 1/2. A three-dimensional numerical simulation is carried out using Direct Numerical Simulation and Large Eddy Simulation over the Reynolds number range of 300 ≤ Re ≤ 30,000. The results obtained from the numerical simulations have fulfilled a gap of data in the literature. Further, the relationships of the lift and drag coefficients and the Strouhal number with the blockage ratios are also revealed. An interesting phenomenon observed in the wake is an inversion of von Kármán vortex street, which appears at all the blockage ratios under consideration for 300 ≤ Re ≤ 1,000, due to the influence of the wall shear layers. It is found that the invert location where the reverse Kármán vortex street takes place is mainly dependent on the blockage ratio. To validate the numerical results, a Particle Image Velocimetry (PIV) measurement is conducted at Re < 1,300 in a water flume using a high-speed camera and a continuous wave laser. The experimental data have successfully validated the numerical results at different blockage ratios. Further, two vortex shedding modes including symmetric shedding and alternating shedding modes are observed at β = 1/3 and 1/2.
In the second investigation, both experimental measurement and numerical simulation are carried out for flows over a highly confined circular cylinder at a fixed blockage ratio of β = 0.6. A PIV measurement is conducted using the previous setup for Re < 1,500. It is found that the vortex shedding in the wake switches between the symmetric and alternating shedding modes, which may be due to the presence of low-frequency mode perturbations in the experimental setup. It is understood that at this blockage ratio, the shear layers separating from the cylinder become excessively long and susceptible to upstream turbulence, and the dynamics of the separated shear layers control the wake dynamics. A mixing layer theory is adopted with adjustment to predict the behaviours of the highly confined flows, which show very good agreement with the PIV results. A separate experiment is conducted at Re = 927 to measure the drag coefficient of the confined cylinder using strain gauges. The results from the force measurement are consistent with the numerical data.
Inspired by the PIV measurement, a dedicated numerical simulation is conducted at β = 0.6 and Re = 1,000 to examine the responses of the flows over a highly confined cylinder at various excitation frequencies. It is revealed that the vortex shedding frequency and the excitation frequency are locked on over four sub-regimes of the excitation frequencies. It is also found that the responses of the separated shear layers to the excitations determine the lock-on behaviour, which is remarkably different from that of an unconfined cylinder.
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Park, Suhyeon. « Experimental Investigation of Flow and Wall Heat Transfer in an Optical Combustor for Reacting Swirl Flows ». Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82349.
Texte intégralRésumé :
The study of flow fields and heat transfer characteristics inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers because of the harsh environment at high temperatures. Design improvements of gas turbine combustors for higher efficiency, reduced pollutant emissions, safety and durability require better understanding of combustion in swirl flows and thermal energy transfer from the turbulent reacting flows to solid surfaces. Therefore, accurate measurement and prediction of the flows and heat loads are indispensable.
This dissertation presents flow details and wall heat flux measurements for reacting flow conditions in a model gas turbine combustor. The objective is to experimentally investigate the effects of combustor operating conditions on the reacting swirl flows and heat transfer on the liner wall. The results shows the behavior of swirling flows inside a combustor generated by an industrial lean pre-mixed, axial swirl fuel nozzle and associated heat loads.
Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Experiments were conducted with various air flow rates, equivalence ratios, pilot fuel split ratios, and inlet air temperatures. Methane and propane were used as fuel. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a main part of the investigation. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows. Comparison between reacting and non-reacting flows yielded very striking differences. Self-similarity of the flow were observed at different operating conditions.
Flow temperature measurements with a thermocouple scanning probe setup revealed the temperature distribution and flow structure. Features of premixed swirl flame were observed in the measurement. Non-uniformity of flow temperature near liner wall was observed ranging from 1000 K to 1400 K. The results provide insights on the driving mechanism of convection heat transfer.
As a novel non-intrusive measurement technique for reacting flows, flame infrared radiation was measured with a thermographic camera. Features of the flame and swirl flow were observed from reconstructed map of measured IR radiation projection using Abel transformation. Flow structures in the infrared measurement agreed with observations of flame luminosity images and the temperature map. The effect of equivalence ratio on the IR radiation was observed.
Liner wall temperature and heat transfer were measured with infrared thermographic camera. The combustor was operated under reacting condition to test realistic heat load inside the industrial combustors. Using quartz glass liner and KG2 filter glass, the IR camera could measure inner wall surface temperature through the glass at high temperature. Time resolved axial distributions of inner/outer wall temperature were obtained, and hot side heat flux distribution was also calculated from time accurate solution of finite difference method.
The information about flows and wall heat transfer found in this work are beneficial for numerical simulations for optimized combustor cooling design. Measurement data of flow temperature, velocity field, infrared radiation, and heat transfer can be used as validation purpose or for direct inputs as boundary conditions. Time-independent location of peak location of liner wall temperature was found from time resolved wall temperature measurements and PIV flow measurements. This indicates the location where the cooling design should be able to compensate for the temperature increase in lean premixed swirl combustors.
The characteristics on the swirl flows found in this study points out that the reacting changes the flow structure significantly, while the operating conditions has minor effect on the structure. The limitation of non-reacting testing must be well considered for experimental combustor studies. However, reacting testing can be performed cost-effectively for reduced number of conditions, utilizing self-similar characteristics of the flows found in this study.Ph. D.
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Meunders, Andreas [Verfasser]. « A study on buoyancy-driven flows : Using particle image velocimetry for validating the Fire Dynamics Simulator / Andreas Meunders ». Wuppertal : Universitätsbibliothek Wuppertal, 2016. http://d-nb.info/1120340047/34.
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Skulina, David John. « A study of non-linear acoustic flows at the open end of a tube using particle image velocimetry ». Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/12964.
Texte intégralRésumé :
The radiation of sound from the open end of a resonant tube is relatively well understood at low acoustic amplitudes in terms of linear acoustics. At high acoustic amplitudes, however, additional non-linear loss mechanisms such as vortex shedding and jet streaming are known to affect the sound field at the open end and the efficiency with which a standing wave is maintained within a tube. This has implications in a number of fields, notably in musical instrument design and in the automotive industry. Particle Image Velocimetry (PIV) is used to acquire full-field instantaneous velocity information of the acoustic particle velocity field at the open end of a cylindrical tube in which a high amplitude should field has been generated by a loudspeaker. Five different tube terminations are used to examine the effect of varying the geometry of the open end on the flow phenomena observed. A qualitative identification of number of flow regimes is made and a number of techniques are used to evaluate the non-linear losses numerically. PIV results are used in combination with pressure measurements to evaluate the termination impedance and a comparison is drawn with results made by conventional methods. Jet streaming is investigated and the associated energy dissipation is estimated. Vortex sound theory is then used to measure the acoustical losses caused by boundary layer separation and the resultant generation of vortex structures.
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Hattori, Tae. « Investigation into Stability, Transition and Turbulence of Thermal Plumes ». Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/9338.
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In this thesis, the stability, transition and turbulence of thermal plumes were investigated by numerical simulation. Experiments were also conducted, but only for the validation of the simulation code being used. The effect of variable transport properties on a large eddy simulation of a turbulent axisymmetric plume was examined, and it was shown that an in-house incompressible Navier-Stokes solver, which is based on a standard Smagorinsky LES model, with the effects of variable properties incorporated using a modified Sutherlands law, predicts the correct statistical behaviours of the turbulent plume. The near-field puffing instability in thermal planar plumes, which had received little attention in the literature, was investigated by direct numerical simulation. The associated lapping flow instability, forming bulge structures over a heated floor section, was studied using a channel flow model, which allows the lapping flow velocity to be varied. The parametric dependencies were found for the bulge formation and the oscillation frequencies in the lapping flow. Further, the Prandtl number dependent transitional behaviours in the near-field were investigated, and direct stability analysis was conducted to study the lapping flow and stem instabilities. Experiments using a shadowgraph technique and an in-house, two-dimensional, two-component particle image velocimetry, with water as the working fluid, provided validations for the near-field unsteady behaviours of thermal plumes. A ventilated filling box flow with a transitional planar plume was also investigated by direct numerical simulation. A mapping of transitional flow behaviours was obtained, and the parametric dependencies of turbulence statistics and mean flow characteristics were investigated. The three-dimensionality was shown to have only minor effects on the transitional ventilated filling box flows being considered.
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Apsilidis, Nikolaos. « Experimental Investigation of Turbulent Flows at Smooth and Rough Wall-Cylinder Junctions ». Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/71713.
Texte intégralRésumé :
Junction flows originate from the interaction between a fluid moving over a wall with an obstacle mounted on the same surface. Understanding the physics of such flows is of great interest to engineers responsible for the design of systems consisting of wall-body junctions. From aerodynamics to turbomachinery and electronics to bridge hydraulics, a number of phenomena (drag, heat transfer, scouring) are driven by the behavior of the most prominent feature of junction flows: the horseshoe vortex system (HVS). Focusing on turbulent flows, the complex dynamics of the HVS is established through its unsteadiness and non-uniformity. The fundamentals of this dynamically-rich phenomenon have been described within the body of a rapidly-expanding literature. Nevertheless, important aspects remain inadequately understood and call for further scrutiny. This study emphasized three of them, by investigating the effects of: model scale, wall roughness, and bed geometry. High-resolution experiments were carried out using Particle Image Velocimetry (PIV). Statistical analyses, vortex identification schemes, and Proper Orthogonal decomposition were employed to extract additional information from the large PIV datasets. The time-averaged topology of junction flows developing over a smooth and impermeable wall was independent of the flow Reynolds number, Re (parameter that expresses the effects of scale). On the contrary, time-resolved analysis revealed a trend of increasing vorticity, momentum, and eruptions of near-wall fluid with Re. New insights on the modal dynamics of the HVS were also documented in a modified flow mechanism. Wall roughness (modeled with a permeable layer of crushed stones) diffused turbulence and vorticity throughout the domain. This effect manifested with high levels of intermittency and spatial irregularity for the HVS. Energetic flow structures were also identified away from the typical footprint of the HVS. Finally, a novel implementation of PIV allowed for unique velocity measurements over an erodible bed. It was demonstrated that, during the initial stages of scouring, the downflow at the face of the obstacle becomes the dominant flow characteristic in the absence of the HVS. Notwithstanding modeling limitations, the physical insight contributed here could be used to enhance the design of systems with similar flow and geometrical characteristics.Ph. D.