The quenching of undesired flames by cold surfaces has been investigated for more than a century. The current quenching theory can predict simple configurations, this is not the case for real environments such as fuel management systems. Flames are sensitive to numerous parameters, such as fuel, mixture fraction, pressure, temperature, flow properties, acoustics, radiation, and surface interactions. The effects of some of these parameters are very well documented but there is a lack of information regarding the effects of acoustics and flow. This dissertation work will focus on improving the understanding of flow effect on the quenching of premixed gaseous flames. First, the effect of apparent velocity on flame quenching was investigated for different fuels and equivalence ratios. An experimental facility is designed such that the apparent flame velocity at which the flame enters and propagates through the channel can be varied without changing the initial mixture condition. High-speed (15,000 frames per second (FPS)) Schlieren and dynamic pressure measurement were used to measure the apparent flame velocity and to assess the flame quenching, respectively. This study showed that the high-speed laminar flames are harder to quench compared to self-propagating and turbulent flames. A similar trend was obtained for all the conditions investigated, lean and stoichiometric methane-air, lean propane-air, and lean ethylene-air mixtures. Further investigation was carried out to understand the quenching of high-speed laminar flames. The flame propagation through the channel was investigated using Hydroxyl (OH) planar laser induced fluorescence (PLIF). This study showed that the OH intensity fell below the detection threshold in the later part of the channel when quenching is observed. Then, the influence of heat transfer was investigated using spatial and temporal evolution of the temperature in the quenching channel. A high-speed (10 kHz) filtered Rayleigh scattering (FRS) technique was used to measure the one-dimensional time-resolved temperature profile. Three different channel heights (H = 1.3, 1.5, 2.0 mm) were investigated. Based on the evolution of the temperature profile in the quenching channel, a new parameter was identified and the importance of its evolution on the flame quenching was discussed.

Establishing a clean and renewable energy supply is the preeminent engineering challenge of our time. Turbines, in some form, are responsible for more than 98 percent of all electricity generated in the United State and 100 percent of commercial and military air transport. The operation of these engines is clearly responsible for significant consumption of hydrocarbon fuels and, in turn, emission of green house gases into the atmosphere. With such wide-scale implementation, it is understood that even the smallest increase in the operating efficiency of these machines can lead to enormous improvements over the current energy situation. These effects can extend from a reduction in the emission of greenhouse gases to lessening the nation's dependence of foreign energy sources to lower energy prices for the consumer. The prominent means of increasing engine efficiency is by raising the 'Turbine Inlet Temperature' ' the temperature of the mainstream flow after combustion, entering the first stage of the turbine section. The challenge is presented when these temperatures are forced beyond the allowable limits of the materials inside the machine. In order to protect these components, active cooling and protection methods are employed. The focus of this work is the development of more efficient means of cooling 'hot' turbine components. In doing so, the goal is to maximize the amount of heat removed by the coolant while minimizing the coolant mass flow rate: by removing a greater amount of heat with a lower coolant mass flow rate, more compressed air is left in the mainstream gas flow for combustion and power generation. This study is an investigation of the heat transfer augmentation through the fully-developed portion of a narrow rectangular duct (AR=2) characterized by the application of dimples to the bottom wall of the channel. Experimental testing and numerical modeling is performed for full support and validation of presented findings. The geometries are studied at channel Reynolds numbers of 20000, 30000, and 40000. The purpose is to understand the contribution of dimple geometries in the formation of flow structures that improve the advection of heat away from the channel walls. Experimental data reported includes the local and Nusselt number augmentation of the channel walls and the overall friction augmentation throughout the length of the duct. Computational results validate local Nusselt number results from experiments, in addition to providing further insight to local flow physics causing the observed surface phenomena. By contributing to a clearer understanding of the effects produced by these geometries, the development of more effective channel-cooling designs can be achieved.

La miniaturisation de plus en plus poussée (micro et nano) des systèmes mécanique connaît un important développement depuis une dizaine d'années. Leur conception et réalisation nécessite une connaissance approfondie des écoulements micro-fluidiques. Dans le domaine énergétique, le rendement d'un moteur thermique se dégrade sérieusement lors d'une réduction d'échelle. En effet, les pertes de chaleur pariétales peuvent devenir aussi importantes que l'énergie libérée. Une voie prometteuse consiste à utiliser les ondes de choc / détonation pour accélérer la libération d'énergie. Dans ce cas, la détonation peut être assimilée à une onde de choc inerte, couplée à une zone de réaction, caractérisée par la présence d'instabilités longitudinales et transverses, soumettant ainsi le front de choc à de violentes accélérations / décélérations. L'objectif de la thèse est de mieux appréhender la structure moyenne de la zone de réaction qui s'étend du choc jusqu'à la surface sonique. Sur le plan de la modélisation numérique, les équations de Navier-Stokes compressibles, multi-espèces, réactives sont résolues au sein du solveur CHOC-WAVES développé au CORIA, avec une thermodynamique variables et des coefficients de transport dépendant des espèces. La condition de Chapman-Jouguet généralisée a été élaborée et confirmée par les résultats de simulations numériques dans le cas d'une détonation multidimensionnelle stable. En particulier, il a été montré que les instabilités transverses s'atténuaient avec la réduction d'échelle. A cet effet, un scénario a été proposé pour expliquer le déficit de la vitesse du front de détonation, en se basant sur la structure de la poche subsonique aval, en corrélation avec l'épanouissement de la couche limite. Ce schéma partage de fortes similitudes avec la macro-détonation, tout en gardant des différences. En particulier, il a été montré que la forte vorticité, produite au niveau de la singularité de Prandtl-Meyer, souvent négligée dans les modèles de macro-détonation, diffusait au sein de la poche subsonique. Ces résultats tout à fait originaux ont permis une avancée significative dans la compréhension du mécanisme de propagation des fronts de détonation stables et confinées. / Progress towards the miniaturization of increasingly advanced micro- and nano-electromechanical systems has highlighted the need for a better knowledge of the design of such devices. knowledge of micro-nano pipe flows is still mandatory. In field of energy power generation, as the systems are scaled down, the thermal efficiency of conventional propellant devices is seriously degraded due to significant heat losses which can cause the combustion extinction. A promising approach is to use shock or detonation waves in gazeous media to enhance chemical reaction rates. A detonation is a rapid regime of burning in which a strong shock ignites the fuel and the burning proceeds to equlibrium behind the shock, while the energy released continues to drive the shock. It is also characterized by the presence of longitudinal and transverse instabilities, thereby subjecting the shock front to violent deceleration / acceleration. The objective of this thesis is to better understand the mean structure of the reaction zone that extends from the shock to the sonic surface. As for numerical modelling, the compressible multi-species reactive Navier-Stokes equations are solved using an in-house code "CHOC-WAVES", including variable thermodynamic and transport coefficients depending on the species. The Generalized Chapman-Jouguet condition was developed and corroborated by the numerical results in the case of stable multidimensionnal detonation. More specially, it was shown that the transverse instabilities are attenuated with the scale reduction.To this end, a scenarion, based on the structure of downstream subsonic pocket, which is correlated to the development of the boundary layer, has been proposed to explain the deificit of the detonation from velocity. This scheme shares many similarities with the macro-detonation, while keeping some differences. In particular, it was shown that the strong vorticity, generated at the Prandlt-Meyersingularity and often neglected in macro-detonation models, diffuses in the subsonic pocket. The present contribution enables us to shade more physical insight for the propagation of stable and confined detonation fronts.