Background: Nowadays, one of the medical problem is rolling cell adhesion. Rolling cell adhesion is a complex process that requires the analysis of the challenging environment such as body fluid and is the process responsible for recruiting the cell to specific organs. In order to explore the rolling cell adhesion, mathematical model is proposed. Different image processing methods are created, such as optical flow - Lucas Kanade algorithm, and other type of methods related to mechanical fluid, namely PIV (Particle Image Velocimetry). Aim: The aim of this master thesis is the identification of challenges while using PIV in live cell images and propose the algorithm, which may analyze the rolling cell adhesion problem. Methods: In order to understand properly the rolling cell adhesion problem from biological site, literature review combined with the expert consultation is performed. According to gather information, mathematical model is proposed. Particle Image Velocimetry is explained according to literature review, where at the beginning the expert recommends some books as a primary research. As a result of this research, PIV challenges are identified and generally PIV idea is explained. Then two experiments are performed. The first experiment evaluates detection algorithms and the second one, analyses track algorithm vs. PIV. In order to evaluate the mentioned algorithms, some evaluation method are selected and some criteria are defined. Unfortunately the found methods are not perfect, therefore a new method related to performance evaluation using time series is proposed. Thesis result: The result of this thesis is a proposition of the algorithm, which can be used in the rolling cell adhesion. The algorithm is formed according to the detailed exploration of the rolling cell adhesion and analysis of the selected algorithms related to the image analysis during the theoretical research and experiments.

D'une part, les équations de Navier-Stokes permettent de décrire les écoulements fluides, la littérature est riche de méthodes numériques permettant la résolution de celle-ci. D'autre part, nous sommes capables de mesurer de manière non-intrusive différentes caractéristique d'un écoulement (champ de vitesse et pression, etc.). Dans le cadre de cette thèse, nous nous intéressons aux techniques d'assimilation de données qui combinent les modèles numériques avec les observations afin de déterminer une meilleure approximation du système. Cette thèse s'articule autour de l'assimilation de donnée variationnelle (4DVar) qui est plus précise par construction. Nous avons mené une première application sur la reconstruction de la hauteur et vitesse de la surface libre d'un fluide contenu dans un récipient rectangulaire à fond plat. L'écoulement est modélisé par les équations de shallow water et résolues numériquement. Les observations de l'évolution de la hauteur de la surface libre ont été prélevées par un capteur de profondeur (Kinect). Nous avons comparé les résultats de la reconstruction par 4DVar avec plusieurs version de la méthode d'assimilation hybride 4DEnVar. Enfin, nous avons appliqué la technique 4DVar à la reconstruction volumique de l'aval d'un sillage de cylindre à Reynolds 300. L'écoulement turbulent a été simulé par un code DNS parallèle Incompact3D. La reconstruction a été effectué en combinant tout d'abord des observations synthétiques en trois dimension, puis en combinant des observations de plans orthogonales en stéréo PIV. / In the one hand, flow dynamics are usually described by the NavierStokes equations and the literature provides a wide range of techniques to solve such equations. On the other hand, we can nowadays measure different characteristics of a flow (velocity, pressure, temperature etc...) with non-intrusive Particle Image Velocimetry techniques. Within this thesis, we take interest in the data assimilation techniques, that combine a dynamics model with measurements to determine a better approximation of the system. This thesis focus on the classic variational assimilation technique (4DVar) which ensures a high accuracy of the solution by construction. We carry out a first application of the 4DVar technique to reconstruct the characteristics (height and velocity field) of a uni directional wave at its free surface. The fluid evolution is simulated by the shallow water equations and solved numerically. We use a simple experimental setup envolving a depth sensor (Kinect sensor) to extract the free surface height. We compared the results of the 4DVar reconstruction with different versions of the hybrid data assimilation technique 4DEnVar. Finally, we apply the 4DVar technique to reconstruct the downstream of a three dimensional cylinder wake at Reynolds 300. The turbulent flow is simulated by the high-performance multi-threading DNS code Incompact3d. This dynamics model is first combined with synthetic three dimensional observations, then with real orthogonal-plane stereo PIV observations to reconstruct the full three dimensional flow.

[pt] Neste trabalho foi desenvolvido um sistema para medição de campos instantâneos de velocidade em regiões extensas do escoamento de fluidos. A técnica utilizada foi a velocimetria por imagem de partículas. Nesta técnica, as medidas de velocidade são obtidas a partir do registro da imagem de partículas traçadoras previamente distribuídas no fluido e iluminadas externamente por um plano de luz pulsada. As imagens capturadas são digitalizadas e processadas com algoritmos numéricos especialmente desenvolvidos para este fim. Estes algoritmos empregam técnicas de correlação cruzada de imagens ou de autocorrelação de imagens. Testes do programa desenvolvido foram realizados com imagens de escoamentos geradas em computador. Um sistema experimental foi desenvolvido para capturar imagens de diversos escoamentos teste de baixa velocidade. Os resultados obtidos foram satisfatórios. / [en] The present work describes the development and testo f a whole-field velocimetry system for measuring transient velocity fields in extensive flow regions. The technique employed is known as Particle Image Velocimetry. In this technique, double-exposure images of tracer particles distributed in the fluid and externally illuminated are registered in film or electronic camera. The images are digitized and processed by specially developed computer algorithms based on cross-correlation and autocorrelation techniques. The computer program developed was tested against computer generated flow images. A experimental setup was constructed to capture and analyze several real flow images. The tests conducted with several low-velocity flows yielded satisfactory results.

In this study, experimental data was collected in order to create a test case that can be used to validate computational fluid dynamics (CFD) simulations and the individual models used therein for gas turbine combustor applications. In many cases, the CFD results of gas turbine combustors do not correlate well with experimental results. For this reason, there is a requirement to test the simulation method used before CFD can successfully be used for combustor design. This test case encompasses all the features of a gas turbine combustor such as a swirler, primary, secondary and dilution holes as well as cooling rings. Experiments were performed on the same combustor geometry for both non-reacting and reacting flows. The non-reacting flow experiments consisted of stereoscopic particle image velocimetry (PIV) measurements performed at various planes in the three zones of the combustor. Data was collected on planes, both in line with the holes and in between the holes of each zone. For the reacting experiments, the temperatures on the outlet plane were measured using a thermocouple rake, thus a temperature contour plot on the outlet plane was produced. Further, the combustor can was modified with passive inserts, which were tested to determine their influence on the outlet temperature distribution during reacting runs. In this set-up, the outlet velocity profiles were also measured using a Pitot tube during both non-reacting and reacting flows. In addition to the outlet temperature distribution and velocity profiles, images of the flame patterns were captured, which showed the positions of flame tongues, fluctuating flames and steady flames. Carbon burn patterns on the walls of the combustor liner were also captured. From the data collected during the reacting runs, the pattern factor, profile factor, overall pressure loss and pressure loss factor were calculated. The non-reacting experiments performed using the PIV, produced three-dimensional velocity vector fields throughout the combustor. These experiments were performed at various flow rates, which gave an indication of which features of the combustor flow were affected by the flow rate. When comparing the individual PIV images alongside one another, the temporal nature of the combustor flow was also evident. The reacting experiments revealed a hot region of exhaust gas around the outer edge of the exhaust while there was a cooler region in the centre of the outlet flow. The PIV flowfield results revealed the reason for then hot outer ring-like region was due to the path the hot gasses would take. The hot combustor gas from the primary zone diverges outwards in the secondary zone then is further forced to the outside by the dilution recirculation zone. The hot flow then leaves the combustor along the wall while the cooler air from the jets leaves the combustor in the centre. The experiments performed produced a large variety of data that can be used to validate a number of aspects of combustor simulation using CFD. The non-reacting experimental data can be used to validate the turbulence models used and to evaluate how well the flow features were modelled or captured during the non-reacting stage of the combustor simulation process. The typical flow features such as jet penetration depths and the position and size of the recirculation regions are provided for effective comparison. The thermal results presented on the outlet plane of the combustor can be used for comparison with CFD results once combustion is modelled. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

Hydroelectricity plays an important role to balance the stability of grid network.  In order to improve the stability of presently high loaded grids, hydropower plants are being operated over a wide range of operations and experiencing frequent start-stop, load rejection, and load acceptance. The turbines need to sustain sudden change in their operating condition to balance the grid frequency. Francis turbines have been widely used because of their wider operating range and higher stability in operation during rapid load variation. This has resulted in severe damage to the turbines as they are not normally designed to operate under such transient conditions. Several low and high frequency pressure fluctuations prevail during transients operating conditions. Generally, wall pressure measurements are performed which may not provide sufficient information to investigate the flow instabilities related to these fluctuations. Thus, the main objective of the present work is to simplify and perform optical measurements in a turbine during transient operating conditions to investigate the flow field. The measurements have been performed at the Water Power Laboratory using a high head model Francis turbine. The turbine is a 1:5.1 scale down model of a prototype operating at the Tokke Power Plant, Norway. The model runner diameter, net head, and discharge at the best efficiency point (BEP) were 0.349 m, 12 m, and 0.2 m3 s-1, respectively. A total ten pressure sensors were mounted at different locations namely, turbine inlet, vaneless space, and draft tube. The data were acquired at a sampling rate of 5 kHz. The instruments and sensors have been calibrated according to guidelines available in IEC standards. The determined total uncertainty in the measurement of hydraulic efficiency was ±0.15% at BEP condition. The velocity measurements in the draft tube cone were performed using a 2D PIV system and the images were sampled at a rate of 40 Hz.      Steady state measurements were carried out considering the realistic design and off-design operating conditions of the prototype turbine. Therefore, the angular speed of the runner was maintained constant for all steady state conditions during the measurements. The maximum hydraulic efficiency (92.4%) was observed at nED = 0.18, QED = 0.15, and a = 9.8º, which is named BEP. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space, runner, and the draft tube. The fluctuations due to rotor-stator interaction (RSI) were observed to be most dominating at high load condition, however, fluctuations due to the rotating vortex rope (RVR) at part load (PL) condition. Two different modes (synchronous and asynchronous) modes of vortex rope are observed at PL condition of the turbine. An asymmetry in the flow leaving the runner was detected at both design and off-design conditions, with a stronger effect during off-design operating condition. Numerical simulations of the model turbine were carried out at PL operating condition. The simulations were performed using two turbulence models, standard k-ε and SST k-ω, with high-resolution advection scheme. The numerical pressure values obtained with both standard k-ε model and SST k-ω showed a small difference with the experimental values. The amplitudes of numerical pressure values were higher (~2.8%) in the vaneless space and lower (~5.0%) in the draft tube than the experimental values. The frequencies of the RSI and RVR were well captured in the turbine but the amplitudes were overestimated.   During load rejection from BEP to PL, the plunging mode of the vortex rope was observed to appear first in the system than that of the rotating mode. Whereas during the load acceptance from PL to BEP, both the modes were observed to disappear simultaneously from the system. In the velocity data, the axial velocity only contributed to the development of the plunging mode and radial velocity to the rotating mode. The region of low velocity, stagnation point, flow separation, recirculation, oscillating flow and high axial velocity gradients were well captured in the system during the transients. The induced high-velocity gradients during the load acceptance from BEP to HL was observed to develop a vortex core in the draft tube. During startup and shutdown, the guide vanes angular position was moved from one to another steady state condition to achieve the minimum load condition of the turbine. At this condition, the generator of the turbine was magnetized at the synchronous speed during startup and shutdown, respectively. The frequency of wave propagation was observed to vary with the runner angular speed during startup and complete shutdown of the turbine. Comparatively high-pressure fluctuations in the draft tube were observed during the guide vane movement from the high discharge conditions. Some unsteady phenomena such as the formation of dead velocity zone, backward flow, and flow oscillations were observed during startup and shutdown of the turbine.   The current work has been also used to continue a series of workshops, i.e., Francis-99. The first workshop was held on December 2014 with the cooperation of LTU and NTNU. The measurements performed in this work were used for the second workshop which was held on December 2016. The investigations presented in this thesis will be further explored in the third workshop scheduled for December 2018.

The turbulent boundary layer is an aspect of fluid flow which dominates the performance of many engineering systems - yet the analytic solution of such flows is intractable for most applications. Our understanding of boundary layers is therefore limited by our ability to simulate and measure them. Tomographic Particle Image Velocimetry (TPIV) is a recently developed technique for direct measurement of fluid velocity within a 3D region. This allows new insight into the topological structure of turbulent boundary layers. Increasing Reynolds Number increases the range of scales at which turbulence exists; a measurement technique must have a larger 'dynamic range' to fully resolve the flow. Tomographic PIV is currently limited in spatial dynamic range (which is also linked to the spatial and temporal resolution) due to a high degree of noise. Results also contain significant bias error. This work proposes a modification of the technique to use more than two exposures in the PIV process, which (for four exposures) is shown to improve random error by a factor of 2 to 7 depending on experimental setup parameters. The dynamic range increases correspondingly and can be doubled again in highly turbulent flows. Bias error is reduced by up to 40%. An alternative reconstruction approach is also presented, based on application of a reduction strategy (elimination of coefficients based on a first guess) to the tomographic weightings matrix Wij. This facilitates a potentially significant increase in computational efficiency. Despite the achieved reduction in error, measurements contain non-zero divergence due to noise and sampling errors. The same problem affects visualisation of topology and coherent fluid structures. Using Projection Onto Convex Sets, a framework for post-processing operators is implemented which includes a divergence minimisation procedure and a scale-limited denoising strategy which is resilient to 'false' vectors contained in the data. Finally, developed techniques are showcased by visualisation of topological information in the inner region of a high Reynolds Number boundary layer (δ+ = 1890, Reθ = 3650). Comments are made on the visible flow structures and tentative conclusions are drawn.

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Thermoacoustic devices are a group of systems that make use of the thermoacoustic effect to achieve an energy conversion between thermal and acoustic energy. The thermoacoustic effect occurs when a solid boundary is introduced into an acoustic field, and a non-zero net heat transportation takes place while the net mass transfer remains null. Thermoacoustic technologies are gaining an increasing research interest because of their potential applications for building alternative prime movers or heat pumps which do not use working fluids causing environmental damage and require very little maintenance due to their lack of moving part. However, the operation of this type of system is yet to be fully understood: fluid flow and heat transfer processes within the system components such as thermoacoustic stacks and heat exchangers still require a lot of attention. The performance of the system working with relatively low amplitude acoustic wave can be predicted by the linear thermoacoustic theory, which is already well developed. However, a high amplitude acoustic wave is usually required in order to achieve high power density or high power output. Unfortunately, the performance of such systems can be seriously degraded due to nonlinear effects, such as turbulence, minor loss or high proportion of harmonics. The lack of understanding of these effects impedes the design and construction of high efficiency systems. The work described in this thesis is focused on the study of flow phenomena taking place around parallel plate stack placed in a standing wave thermoacoustic resonator, by using advanced flow diagnostics techniques such as particle image velocimetry (PIV) and hot wire anemometry (HWA). In order to carry out the experimental study, a standing wave thermoacoustic device working at relatively low frequency of 13.1Hz was designed, commissioned and tested. The frequency response of this device was carefully investigated and compared with the analytical results using linear acoustic equations and a linear model of the loudspeaker. A further comparison with the analytical results obtained with the modelling tool DeltaEC (Design Environment for Low-amplitude Thermoacoustic Energy Conversion) was also presented. The resonator was driven from low to large pressure amplitudes with drive ratios up to 10%. A good agreement is obtained for small amplitudes, but the discrepancies become larger when the driving amplitude is increased. The analysis reveals that the large discrepancy at high amplitude can be attributed to minor losses. Following the above preliminary work, a more comprehensive study of the flow field around parallel-plate stacks was conducted by means of PIV and HWA. It was shown that the flow around the two studied parallel-plate stacks exhibits rather complicated flow features when the amplitude of the acoustic oscillation varies. Symmetrical and asymmetrical vortex shedding phenomena are observed and two distinct modes of generating 'vortex streets' are identified. It shown that a velocity related parameter such as the Reynolds number, defined on the plate thickness and the velocity amplitude at the entrance to the stack, and a geometrical parameter are not sufficient to define the flow characteristics in this type of flow problem. It is also proposed to introduce an extra frequency related parameter such as the Keulegan-Carpenter number (KC) and to carry out a similarity analysis in order to understand better the physics behind the flow phenomena and their controlling parameters. Typical ensemble-averaged velocity fields are used in the analysis above. However, the detailed flow features obtained from the ensemble averaged flow fields and the instantaneous flow fields could be different in a substantial way. The flow behaviour, its kinematics, dynamics and scales of turbulence, therefore are further investigated by using the classical Reynolds decomposition to separate the instantaneous velocity fields into ensemble-averaged mean velocity fields and fluctuations in a set of predetermined phases within an oscillation cycle. The mean velocity field and the fluctuation intensity distributions are investigated over the acoustic oscillation cycle. By using fast Fourier transform (FFT) spatial filtering techniques, the velocity fluctuation is further divided into large- and small-scale fluctuations, and their physical significance is discussed. The physics behind the flow phenomena are further studied by carrying out an analysis of the wake flow during the ejection part of the flow cycle, where either closed re-circulating vortices or alternating vortex shedding can be observed. A similarity analysis of the governing Navier-Stokes equations is then undertaken in order to derive the similarity criteria governing the wake flow behaviour. Similarity numbers including two types of Reynolds number, the KC number and a non-dimensional stack configuration parameter are considered. The influence of these parameters on the flow behaviour is discussed by investigating the experimental data obtained, along with additional data from literature.