京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21723号 / 工博第4540号 / 新制||工||1708(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 准教授 竹林 洋史, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

An experimental investigation was performed to ascertain the nature of turbulence in a narrow apex angle isosceles triangular duct. The study involved the design and construction of a low noise, low turbulence wind tunnel that had an isosceles triangular test section with an apex angle of 11.5[degrees]. Experiments involved the measurement of velocity fluctuations using hot wire anemometry and wall pressure fluctuations using a condenser microphone. Measurement of the velocity fluctuations reconfirms the coexistence of laminar and turbulent regions at a given cross section for a range of Reynolds numbers. The laminar region is concentrated closer to the apex while the turbulent region is found closer to the base. The point of transition is a function of the Reynolds number and moves closer to the apex as the flow rate is increased. Moreover, it was found in this investigation that traditional scaling of the turbulent statistical quantities do not hold good in this geometry. Although velocity fluctuations showed distinctive flow regimes, no such distinction could be seen in the dynamic wall pressure data. The nature of the dynamic wall pressure was uniform throughout the entire cross section suggesting that wall pressure fluctuations, unlike the velocity fluctuations, are able to travel from the base to the apex, without being damped. This implies that the relationship between the velocity and the pressure fluctuations applicable in the other systems does not hold well in a narrow apex angle isosceles triangular duct. Further, the typical scaling relationships applied to wall pressure spectra of other geometries doesn't apply in this scenario and the ratio of the RMS pressure fluctuation to the mean shear is much higher compared to a flat plate or pipe flow situation.

Surface mean pressures, oil flow visualization, and 3-velocity-component laser-Doppler velocimeter measurements are presented for a turbulent boundary layer of momentum thickness Reynolds number, 7300 and thickness delta over two circular based axisymmetric bumps of height H = delta and 2delta and one rectangular based symmetric bump of H = 2delta. LDV data were obtained at one plane x/H ¥ 3.26 for each case. Complex vortical separations occur on the leeside and merge into large stream-wise mean vortices downstream for the 2 axisymmetric cases. The near-wall flow (y+ < 90) is dominated by the wall. For the axisymmetric cases, the vortices in the outer region produce large turbulence levels near the centerline and appear to have low frequency motions that contribute to turbulent diffusion. For the case with a narrower span-wise shape, there are sharper separation lines and lower turbulence intensities in the vortical downstream flow. Fine-spatial-resolution LDV measurements were also obtained on half of the leeside of an axisymmetric bump (H/delta = 2) in a turbulent boundary layer. Three-dimensional (3-D) separations occur on the leeside with one saddle separation on the centerline that is connected by a separation line to one focus separation on each side of the centerline. Downstream of the saddle point the mean backflow converges to the focal separation points in a thin region confined within about 0.15delta from the local bump surface. The mean backflow zone is supplied by the intermittent large eddies as well as by the near surface flow from the side of the bump. The separated flow has a higher turbulent kinetic energy and shows bimodal histograms in local and U and W, which appear to be due to highly unsteady turbulent motions. By the mode-averaged analysis of bimodal histograms, highly unsteady flow structures are estimated and unsteady 3-D separations seem to be occurring over a wide region on the bump leeside. The process of these separations has very complex dynamics having a large intermittent attached and detached flow region which is varying in time. These bimodal features with highly correlated local u and w fluctuating motions are the major source of large Reynolds stresses local u2, w2 and -uw. Because of the variation of the mean flow angle in the separation zones, the turbulent flow from different directions is non-correlated, resulting in lower shearing stresses. Farther from the wall, large stream-wise vortices form from flow around the sides of the bump. / Ph. D.

Understanding the physics of mixing for two fluids is a complicated problem and has always been an interesting phenomenon to study. Surface discharge is the oldest, least expensive and simplest way of discharging industrial or domestic wastewater into rivers and estuaries. Because of the lower degree of dilution in surface discharges, critical conditions are more likely to occur. Having a better understanding of the mixing phenomenon in these cases will help to predict the environmental effects more accurately. In this study, surface discharges of jets into waterbodies with or without crossflows were investigated numerically and experimentally. Three-dimensional (3-D) Computational Fluid Dynamics (CFD) models were developed for studying the surface discharge of jets into water bodies using different turbulence models. Reynolds stress turbulence models and spatially filtered Large Eddy Simulation (LES) were used in the numerical models. The effects of inclusion of free surface water in the CFD models on the performance of the numerical model results were investigated. Numerical model results were compared with the experimental data in the literature as well as the experimental works performed in this study. Experimental works for buoyant and non-buoyant surface discharge of jets into crossflow and stagnant water were conducted in this study. A new setup was designed and built in the Civil Engineering Hydraulics Laboratory at the University of Ottawa to perform the desired experiments. Stereoscopic Particle Image Velocimetry (Stereo-PIV) was used to measure the instantaneous spatial and temporal 3-D velocity distribution on several planes of measurement downstream of the jet with the frequency of 40 Hz. Averaged 3-D velocity distribution was extracted on different planes of measurement to show the transformation of the velocity vectors from a “jet-like” to a “plume-like” flow regime. Averaged 3-D velocity distribution and streamlines illustrated the flow transformation of the surface jets. Experimental results detected the formation and evolution of vortices in the surface jet’s flow structure over the measurement zone. Additional turbulent flow characteristics such as the turbulent kinetic energy (k), turbulent kinetic energy dissipation rate (ϵ), and turbulent eddy viscosity (υt) were calculated using the measured time history of the 3-D velocity field.

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L'interaction fluide structure est présente dans beaucoup de problèmes industriels, dans les domaines d'ingénierie mécanique, civile ou biomécanique. Même si les performances informatiques s'améliorent considérablement et que les méthodes en mécanique numérique gagnent en maturité, certaines difficultés ne permettent pas encore de réaliser des simulations numériques précises. Actuellement deux méthodes numériques gagnent en popularité pour la simulation numérique d'interactions fluide structure: la méthode de partitionnement et la méthode monolithique. Des résultats de la littérature montrent que la première est efficace et précise mais qu'elle peut rencontrer des problèmes d'instabilité si les ratios de densité sont élevés ou que les géométries sont complexes. Les méthodes d'immersion sont de plus en plus utilisées par la communauté scientifique. Différentes approches ont été développées, dont la Méthode d'Immersion de Volume. Cette méthode permet de faciliter la mise en place des calculs. Ainsi il n'est pas nécessaire de construire des maillages concordant avec la géométrie des objets, et le couplage entre les fluides et les solides se fait naturellement. C'est sur cette analyse qu'a été développé le logiciel Thost. Il permet de simuler des procédés industriels tels que le chauffage de pièces métalliques dans les fours industriels ou la trempe sans caractériser expérimentalement des coefficients de transfert. Le but d'un tel logiciel est de permettre une meilleure compréhension des procédés et ainsi de les optimiser. Cependant les coûts de calcul restant élevés, le but de la thèse est de les diminuer en s'appuyant sur des méthodes numériques innovantes tels que l'adaptation dynamique de maillage anisotrope, des méthodes éléments finis stabilisées ou l'immersion directe des objets à partir de la Conception Assistée par Ordinateur. / Fluid-Structure Interaction (FSI) describes a wide variety of industrial problems arising in mechanical engineering, civil engineering and biomechanics. In spite of the available computer performance and the actual maturity of computational fluid dynamics and computational structural dynamics, several key issues still prevent accurate FSI simulations.Two main approaches for the simulation of FSI problems are still gaining attention lately: partitioned and monolithic approaches. Results in the literature show that the partitioned approach is accurate and efficient but some instabilities may occur depending on the ratio of the densities and the complexity of the geometry. Monolithic methods are still of interest due to their capability to treat the interaction of the fluid and the structure using a unified formulation. In fact it makes the build up of a FSI problem easier as the mesh do not have to fit the geometry of the solids and the transfers are treated naturally.The software Thost has been created based on these analyzes. Thost is a 3D aerothermal numerical software. It has been developped for the numerical simulation of industrial processes like the heating in industrial furnaces as well as quenching. Its target is to model numericaly the thermal history of the industrial pieces in their environment without using any transfer coefficient. However the computational costs are still high and therefore the software is not fully efficient from an industrial point of view to simulate, analize and improve complex processes. All the work in this PhD thesis has been done to reduce the computational costs and optimize the accuracy of the simulations in Thost based on innovatives numerical methods such as dynamic anisotropic mesh adaptation, stabilized finite elements methods and immersing the objects directly from their Computer Aided Design files.

An experimental study of the effects of turbulent flow regime on the flame structure is conducted by using perforated-plate-stabilized hydrogen-piloted lean premixed methane/air turbulent flames. The underlying non-reacting turbulent flow field was investigated using two-dimensional three-components particle imaging velocimetry (2D3C-PIV) with and without three perforated plates. The non-reacting flow data allowed a separation of the turbulent flow regime into axial velocity dominated and vortex dominated flows. A plate with 62\% blockage ratio was used to represent the stream-dominant flow regime and another with 86\% blockage ratio was used to represent the vortex-dominant flow regime. OH laser-induced fluorescence was used to study the effects of the turbulent flow regime on the mean progress variable, flame brush thickness, flame surface density, and global consumption speed. In comparison with the stream-dominant flow, the vortex-dominant flow makes a wider and shorter flame. Also, the vortex-dominant flow has a thicker horizontal flame brush thickness and a thinner longitudinal flame brush thickness. Especially, the horizontal flame brush thickness for the vortex-dominant flow does not follow the turbulence diffusion theory. Then, the vortex-dominant flow shows a relatively constant flame surface density along the stream-wise direction, while the stream-dominant flow shows a decreasing flame surface density. Lastly, the vortex-dominant turbulent flow improves the consumption speed in comparison to the stream-dominant turbulent flow regime with the same velocity fluctuation level.

A degradação da matriz extracelular e de proteínas da parede aórtica associada à inflamação é uma das principais características dos aneurismas da aorta abdominal (AAA). O objetivo deste trabalho foi investigar a participação das metaloproteinases 2 e 9 na formação de AAAs, através de um modelo experimental inédito de indução de AAA em ratos Wistar, desencadeado por duas potenciais causas de secreção e ativação de MMP-2 e 9: alteração do fluxo sanguíneo e lesão vascular externa na aorta. A formação de aneurismas foi observada em 60%-70% dos animais, apresentando diâmetro de 7 a 8 vezes maior que o diâmetro normal da aorta. Histologicamente observou-se remodelamento, intensa resposta inflamatória, destruição maciça de fibras elásticas e aumento da síntese de colágeno na parede aórtica. A expressão de ambas as formas de MMP-2 foram observadas tanto nos AAAs como nos grupos controles, neste com menor atividade, entretanto a expressão da pró e da MMP-9 ativa foram encontradas apenas nos AAAs. Conclusão: Nossos resultados sugerem que tanto as MMP-2 quanto as MMP-9 apresentam importante papel no desenvolvimento de AAA e este novo modelo de indução de AAA, pode ajudar a elucidar os mecanismos que desencadeiam a secreção e ativação das MMP-2 e MMP-9 na formação de aneurismas. / Degradation of extracellular matrix and proteins associated with inflammation of the aortic wall is the main characteristics of the abdominal aortic aneurysms (AAA). The aim of this study was investigate the participation of Metalloproteinase 2 and 9 in AAA formation in Wistar rats. A novel experimental model of AAA was developed, providing two potential causes of MMPs secretion and activation, turbulent flow (caused by surgically induced extrinsic stenosis) and outside vascular injury is detailed described. The days analyzed were the 3rd and the 7th post surgery. Aneurysms were observed to occur in 60-70% of the Group AAA, exhibiting a major transversal diameter to 7 from 8 times larger than controls and sham groups. Histologically, the aneurysms wall showed extensive structural remodeling, intense inflammatory response, massive elastic fibers destruction and abundant collagen deposition. Increased pro- and active MMP-2 was demonstrated in the AAA and controls groups, whereas pro- and active MMP-9 were found to be expressed only in the AAA group. Conclusions: MMP-2 and MMP-9 may have a pivotal role in the development of experimental AAA. This model can help to elucidate the mechanisms which trigger off MMP-2 and MMP-9 secretion and activation causing aneurysms.