Les phénomènes d’interactions choc/couche limite sont dimensionnants pour de nombreuses applications des domaines de l’aéronautique et du spatial. Ils peuvent être associés à la formation de décollements instationnaires à basse fréquence qui n’ont été étudiés jusqu’à présent qu’en géométrie plane. La présente étude vise à caractériser ce type d’interaction en configuration cylindrique. Un outil de simulation numérique directe,basé sur l’extension de schémas hybrides aux différences finies de haute précision (centrés optimisés6/WENO 5) en géométrie curviligne, a été développé et validé à travers divers cas test standards. Une première partie de l’étude se focalise sur l’influence d’un effet de courbure transverse sur le développement des propriétés d’une couche limite supersonique à Mach 3. Il est montré que l’augmentation de la courbure relative de la couche limite tend à réduire l’énergie de fluctuation à basse fréquence près de la paroi, tout en renforçant les perturbations à hautes fréquences dans la zone externe de la couche limite. En comparaison avec le cas plan, la courbure transverse induit une ré-organisation notable des structures de la couche limite et un comportement différent des invariants d’anisotropie des contraintes, mais ne conduit qu’à une légère modification des distributions de contraintes et de l’équilibre global d’énergie cinétique turbulente. Une seconde partie de l’étude se concentre sur la zone d’interaction avec une rampe de compression et le mouvement instationnaire du choc en géométrie de révolution complète. La déformation azimutale du choc est caractérisée dans son mouvement. Elle apparaît essentiellement associée à la fluctuation de la ligne de décollement et l’organisation des structures tourbillonnaires amont. Il est montré que l’énergie des modes azimutaux de pression pariétale fluctuante est plus amplifiée pour les modes d’ordre plus élevé. La contribution à l’effort latéral associé au mode 1 apparaît plus particulièrement marquée à basses fréquences dans la zone amont au point de décollement et à moyennes fréquences en aval de la zone de recollement sur la rampe où les niveaux les plus élevés de fluctuations sont observés. Il est montré que les fluctuations à basses fréquences sont en revanche portées par des modes azimutaux d’ordre de plus en plus élevé à travers la zone d’interaction. / Shock wave/boundary layer interactions (SWBLI) are present in various aerospace engineering applications.They can be associated with separated regions yielding low-frequency unsteadiness, which have mainly been studied in planar geometries. The present study aims at characterizing this type of interaction in a cylindrical configuration. A direct numerical simulation solver has been developed and validated with various test cases. It is based on a high-order finite difference based hybrid schemes (6th order centered scheme/5thorder WENO), extended to curvilinear geometries. Transverse curvature effects on properties of spatially developing supersonic boundary layer at Mach 3 are first examined. It is shown that the increase of the relative curvature of the boundary layer tends to reduce the fluctuation energy at lower frequencies near the wall, while reinforcing the perturbations at higher frequencies in the upper zone of the boundary layer.In comparison with the planar case, the transverse curvature leads to a significant re-organization of the boundary layer structures and a subsequent modified behavior of the invariants of anisotropy turbulent stress tensor. It however only leads to slightly modified distributions of Reynolds stress and a rather similar overall balance of turbulent kinetic energy through the boundary layer. The second part of this study is dedicated to the unsteady motions of the shock/separation zone in a cylinder/compression flare configuration for which the full cylindrical geometry is taken into account. The shock distortions in the azimutal direction appears to be mainly associated to the organization of the upstream vortex structures and the subsequent azimutal fluctuations of the separation line. It is shown that the energy of the fluctuating wall pressure is more amplified for higher order azimutal modes. The contributions to lateral forces, associated to the first mode, are dominated by low-frequencies only upstream of the separation line in the intermittent region. They become more dominant in the middle frequency range downstream of the reattachment zone on the ramp. It is also shown that the low-frequency activity at the wall is progressively due to higher order azimuthal modes through the interaction zone.

The contribution of present research work is to experimentally investigate the effects of blowing ratio and mainstream Mach number/Reynolds number (from 0.6/8.5X10⁵ to 1.0/1.4X10⁶) on the performance of the fan-shaped hole injected turbine blade and vane. The study was operated with high freestream turbulence intensity (12% at the inlet) and large turbulence length scales (0.26 for blade, 0.28 for vane, normalized by the cascade pitch of 58.4mm and 83.3mm respectively). Both convective heat transfer coefficient, in terms of Nusselt number, and adiabatic effectiveness are provided in the results. Present research work also numerically investigates the shock/film cooling interaction. A detailed analysis on the physics of the shock/film cooling interaction in the blade cascade is provided. The results of present research suggests the following major conclusions. Compared to the showerhead only vane, the addition of fan-shaped hole injection on the turbine Nozzle Guide Vane (NGV) increases the Net Heat Flux Reduction (NHFR) 2.6 times while consuming 1.6 times more coolant. For the blade, combined with the surface curvature effect, the increase of Mach number/Reynolds number results in an improved film cooling effectiveness on the blade suction side, but a compromised cooling performance on the blade pressure side. A quick drop of cooling effectiveness occurs at the shock impingement on the blade suction side near the trailing edge. The CFD results indicate that this adiabatic effectiveness drop was caused by the strong secondary flow after shock impingement, which lifts coolant away from the SS surface, and increases the mixing. This secondary flow is related to the spanwise non-uniform of the shock impingement. / Ph. D.

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This thesis is devoted to the optical properties of low-dimensional structures based on such two-dimensional materials as graphene, silicene and phosphorene. We investigate optical properties of a variety of quasi-one dimensional and quasi-zero-dimensional structures, which are promising for future optoelectronics. Primarily we focus on their low-energy optical properties and how these properties are influenced by the structures’ geometry, external fields, intrinsic strain and edge disorder. As a consequence of this endeavor, we find several interesting effects such as correlation between the optical properties of tubes and ribbons whose periodic and ‘hard wall’ boundary conditions are matched and a universal value of matrix element in narrow-gap tubes and ribbons characterizing probability of transitions across the band gap opened up by intrinsic strain originating from the tube’s surface curvature or ribbon’s edge relaxation. The analytical study of the gapped 2D Dirac materials such as silicene and germanene, which have some similarity to the aforementioned quasi-one-dimensional systems in terms of physical description, reveals a valley- and polarization-dependent selection rules. It was also found that absorption coefficient should change in gapped materials with increasing frequency and become a half of its value for gap edge transitions when the spectrum is linear. Our analysis of the electronic properties of flat clusters of silicene and phosphorene relates the emergence and the number of the peculiar edge states localized at zero energy, so-called zero-energy states, which are know to be of topological origin, to the cluster’s structural characteristics such as shape and size. This allows to predict the presence and the number of such states avoiding complicated topological arguments and provides a recipes for design of metallic and dielectric clusters. We show that zero-energy states are optically active and can be efficiently manipulated by external electric field. However, the edge disorder is important to take into account. We present a new fractal-based methodology to study the effects of the edge disorder which can be applied also to modeling of composite materials. These finding should be useful in design of optoelectronic devices such as tunable emitters and detectors in a wide region of electromagnetic spectrum ranging form the mid-infrared and THz to the optical frequencies.