A scaled-up gas turbine vane model was constructed in such a way to achieve a Biot number (Bi) representative of an actual engine component, and experiments were performed to collect temperature data which may be used to validate computational fluid dynamics (CFD) codes used in the design of gas turbine cooling schemes. The physical model incorporated an internal impingement plate to provide cooling on the inner wall surface, and film cooling over the external surface was provided by a single row of holes located on the suction side of the vane. A single row of holes was chosen to simplify the operating condition and test geometry for the purpose of evaluating CFD predictions. Thermocouples were used to measure internal gas temperatures and internal surface temperatures over a range of coolant flow rates, while infra-red thermography was used to measure external surface temperatures. When Bi is matched to an actual engine component, these measured temperatures may be normalized relative to the coolant temperature and mainstream gas temperature to determine the overall cooling effectiveness, which will be representative of the real engine component. Measurements were made to evaluate the overall effectiveness resulting from internal impingement cooling alone, and then with both internal impingement cooling and external film cooling as the coolant flow rate was increased. As expected, with internal impingement cooling alone, both internal and external wall surfaces became colder as the coolant flow rate was increased. The addition of film cooling further increased the overall effectiveness, particularly at the lower and intermediate flow rates tested, but provided little benefit at the highest flow rates. An optimal jet momentum flux ratio of I=1.69 resulted in a peak overall effectiveness, although the film effectiveness was shown to be low under these conditions. The effect of increasing the coolant-to-mainstream density ratio was evaluated at one coolant flow rate and resulted in higher values of overall cooling effectiveness and normalized internal temperatures, throughout the model. Finally, a 1-dimensional heat transfer analysis was performed (using a resistance analogy) in which overall effectiveness with film cooling was predicted from measurements of film effectiveness and overall effectiveness without film cooling. This analysis tended to over-predict overall effectiveness, at the lowest values of the jet momentum flux ratio, while under-predicting it at the highest values. / text

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This study focused on experimentally measuring the performance of a fully cooled, scaled up C3X turbine vane. Experimental measurements focused on investigating row-to-row interactions of coolant jets and the contributions of external film cooling and internal impingement cooling to overall cooling effectiveness. Overall effectiveness was experimentally measured using a thermally scaled, matched Biot number vane model featuring a realistic internal impingement scheme and had normalized surface temperatures that were representative of those found on engine components. A geometrically identical vane was also constructed out of low conductivity polystyrene foam to measure the normalized adiabatic wall temperature, or adiabatic effectiveness of the film cooling configuration. The vanes featured a full coverage film-cooling scheme with a five-row showerhead and 13 total rows of holes containing 149 total coolant holes. This study was the first study to make highly detailed measurements of overall effectiveness on a fully-cooled vane model and expands on previous studies of adiabatic and overall effectiveness on the showerhead and single rows of holes on a matched Biot vane by considering a fully cooled configuration to determine if the results from these previous studies also hold for a fully cooled configuration. Additionally, velocity and thermal fields were measured just upstream of two different suction side rows of holes in order to study the effect of introducing upstream coolant injection. The effects of mainstream turbulence and span-wise location were examined and at the downstream row of holes, the contributions of different rows of holes to the approach flow were compared. This study was the first to measure mean and fluctuating velocity data on the suction side of a turbine vane with upstream coolant injection. Understanding the effects of how upstream injection affects the performance of downstream rows of holes is critical to understanding the film cooling performance on a fully cooled turbine airfoil. / text

This study performed detailed measurements on and around scaled up conducting and adiabatic airfoils with and without film cooling. The conducting vane was a matched Bi airfoil, which accurately scaled the convective heat transfer and conduction through the solid, in order to produce non-dimensional surface temperatures and thermal boundary layers that were representative of an actual engine. Measurements made on all vane models included surface temperature measurements and thermal profiles above the walls. Separate measurements on non-film cooled and film cooled conducting models allowed for the individual contributions of the internal convective cooling and external film cooling to the overall cooling scheme to be quantified. Surface temperature and thermal field measurements above the wall were also performed on a film cooled adiabatic model. For the conducting model with internal cooling only, strong streamwise temperature variations were seen. The surface temperature variations were highly dependent on the local external and internal heat transfer coefficients. Spanwise temperature variations also existed, but were modest in comparison to streamwise variations. Comparing the thermal fields above the film cooled adiabatic and conducting walls allowed for the assumption that the conducting wall would not significantly affect the thermal field in the film cooling jet to be tested. Near the edge of the film cooling jet the developing thermal boundary layer had a clear effect on the overlying gas temperature, suggesting that the common assumption that the adiabatic wall temperature is the appropriate driving temperature for heat transfer to a film cooled wall was invalid. On the jet centerline thermal boundary layer effects were less influential, due to the development of a new, thin boundary layer. This suggested that the adiabatic wall temperature as driving temperature for heat transfer was a reasonable assumption on the jet centerline for most cases tested. As film cooling momentum flux ratio increase, thermal boundary layer effects became more influential on the jet centerline. Additionally, the high resolution surface temperature measurements and thermal field measurements above the wall presented in the current study represent a significant improvement in the data available for validation of computational simulations of conducting turbine airfoils. / text

A numerical model for describing the kinetics of intracellular water transport during cryopreservation was developed. As ice is formed outside the cell, depleting the extracellular liquid of water, the cell will experience an osmotic pressure difference across its membrane, which causes cell dehydration and concomitant shrinkage. Although Mazur (1963) has previously modeled this phenomenon as a two-compartment system with membrane limited transport, the assumption of well-mixed compartments breaks down at large Biot numbers. Therefore, we have developed a numerical solution to this moving-boundary problem, including diffusive transport in the intracellular liquid, in addition to the osmotically driven membrane flux. Our model uses a modified Crank-Nicolson scheme with a non-uniform Eulerian-Lagrangian grid, and is able to reproduce predictions from Mazurs model at low Biot numbers, while generating novel predictions at high Biot numbers. Given that cell damage may result from excessive water loss, our model can be used to predict freezing methods that minimize the probability of cell injury during the cryopreservation process.

Les chocs thermiques provoquent, en général, l’endommagement et la fissuration des matériaux. Ces phénomènes sont observés, par exemple, dans le revêtement de barrière thermique pour les moteurs des turbines, le traitement des surfaces ou la soudure par laser etc. Plusieurs travaux de recherche ont été réalisés au cours des dernières décennies dans l’objectif d’améliorer les performances thermiques et/ou mécaniques des matériaux sous chargement thermique. L’étude des dommages et de la fissuration des matériaux provoqués par les chocs thermiques, tels que le décollement des interfaces et de décohésion de revêtements, a reçu également une attention considérable par les chercheurs. La majorité de ces travaux utilisent les théories classiques, tels que la loi de Fourier de conduction thermique et l'hypothèse de quasi-statique. Malheureusement ces théories ne sont pas adaptées dans le cas de charges extrêmes provoqués par le choc thermique et dans le cas des matériaux micro-fissurés. En conséquence, les théories conventionnelles doivent être enrichies.L'objectif de la thèse est de montrer le rôle crucial des termes non Fourier et les termes inertiels dans le cas de choc thermique sous conditions sévères et dans le cas où les fissures sont petites. Pour cela nous avons mené des études sur deux structures particulières soumises à des chocs thermiques. Chaque structure contient une fissure parallèle au bord libre de la structure située au voisinage de ce dernier. L’influence de la présence de fissure sur la conductivité thermique est prise en compte. Nous avons utilisé la théorie Hyperbolique de transfert de chaleur par conduction pour les champs thermique et mécanique à la place de la théorie traditionnelle classique de Fourier. Pour mener cette étude, nous avons utilisé les Transformées de Laplace et de Fourier aux équations de mouvement et à l’équation de transfert de chaleur. En s’intéressant en particulier aux champs de contrainte au voisinage de la pointe de fissure et aux facteurs d'intensité de contrainte dynamiques. Le problème se ramène à la résolution d’un système d'équations intégrales singulières dans l'espace de Laplace-Fourier. On utilise une méthode d'intégration numérique pour obtenir les différents champs. Nous résolvons ensuite un système d'équations algébriques linéaires. En effectuant des inversions numériques des transformées, nous obtenons les champs de contrainte de température et les facteurs d'intensité de contrainte dynamiques dans le domaine temporel.Les résultats numériques montrent que la conductivité thermique du milieu est affectée par l’ouverture de la fissure ce qui perturberait fortement le champ de température ainsi que l'amplitude des facteurs d'intensité de contrainte dynamiques. Les amplitudes sont supérieures à celles obtenues à partir de la théorie classique de Fourier ainsi que dans le cadre de l'hypothèse quasi-statique. On constate également qu’elles oscillent au cours du temps. La prise en compte simultanément de l’influence de la fissure sur la conductivité thermique, de l'effet non-Fourier ainsi que les effetsIVd'inertie induit un couplage entre les trois phénomènes qui rendrait le problème de choc thermique très complexe. L'effet de barrière thermique induit par la fissure affecte d’une manière significative les champs de température et des contraintes. Les effets d’inertie, et des termes non-Fourier joueraient également un rôle non négligeable lorsque la longueur de la fissure est petite. Comme dans de nombreux problèmes d'ingénierie, l'initiation et la propagation des micro-fissures sont des mécanismes dont il faut tenir compte dans les prévisions de la rupture des structures. Ces effets non conventionnels ne sont plus négligeables et doivent être inclus dans l'analyse de la fracture des structures soumises à des chocs thermiques. / Thermal shock problems occur in many engineering materials and elements, which are used in high temperature applications such as thermal barrier coatings (TBCs), solid propellant of rocket-engine, pulsed-laser processing of materials, and so on. The thermal shock resistance performances and the thermal shock damages of materials, especially the interface debonding and spallation of coatings, have received considerable attention in both analysis and design. Some conventional theories, such as the Fourier’s law of thermal conduction and the quasi-static assumption of the thermoelastic body, may no longer be appropriate because of the extreme loads provoked by the thermal shock. Therefore, these conventional theories need to be enriched or revised.The objective of this thesis is to develop the solutions of the transient temperature field and thermal stresses around a partially insulated crack in a thermoelastic strip under thermal shock loading. The crack lies parallel to the heated traction free surface. The thermal conductivity of the crack gap is taken into account. Hyperbolic heat conduction theory is used in solving the temperature field instead of the traditional Fourier thermal conduction theory. Equations of motion are applied to obtain the stress fields and the dynamic stress intensity factors of the crack. The Laplace and Fourier transforms are applied to solve the thermal-elastic governing equations such that the mixed boundary value problems are reduced to solving a singular integral equations system in Laplace-Fourier space. The numerical integration method is applied to get the temperature field and stress fields, respectively. The problems are then solved numerically by converting the singular integral equations to a linear algebraic equations system. Finally, numerical inversions of the Laplace transform are performed to obtain the temperature field and dynamic stress intensity factors in the time domain.Numerical results show that the thermal conductivity of the crack gap strongly affects the uniformity of the temperature field and consequently, the magnitude of the dynamic stress intensity factors of the crack. The stress intensity factors would have higher amplitude and oscillating feature comparing to those obtained under the conventional Fourier thermal conduction and quasi-static hypotheses. It is also observed that the interactions of the thermal conductivity of the crack gap, the non-Fourier effect and the inertia effects would make the dynamic thermal shock problem more complex. The magnitude of the thermal barrier, non-Fourier and inertia effects is estimated for some practical cases.