The aerodynamics of two-dimensional and three-dimensional flapping motion in hover is analyzed in incompressible, laminar flow at low Reynolds number regime. The aim of this study is to understand the physics and the underlying mechanisms of the flapping motion using both numerical tools (Direct Numerical Simulation) and experimental tools (Particle Image Velocimetry PIV technique). Numerical analyses cover both two-dimensional and three-dimensional configurations for different parameters using two different flow solvers. The obtained results are then analyzed in terms of aerodynamic force coefficients and vortex dynamics. Both symmetric and cambered airfoil sections are investigated at different starting angle of attacks. Both numerical and experimental simulations are carried out at Reynolds number 1000. The experimental analysis is carried out using Particle Image Velocimetry (PIV) technique in parallel with the numerical tools. Experimental measurements are taken for both two-dimensional and three-dimensional wing configurations using stereoscopic PIV technique.

La météorologie de l’espace est un domaine dédié à l’étude de l’impact des variations de l’activité solaire sur l’environnement spatial de la Terre. Celles-ci peuvent avoir des conséquences importantes sur les technologies humaines, comme les réseaux de lignes haute-tension ou les systèmes de télécommunication par satellites. Ces mêmes variations sont également à l’origine des aurores, phénomènes observés dans la haute atmosphère de la Terre au niveau des pôles, au pied des lignes de champ magnétique. Elles vont pouvoir nous servir de traceur dans l’étude des particules so- laires piégées dans l’environnement spatial de notre planète.Les émissions aurorales, complexes, de part leur étalement et différen- ciation en altitude et de leur diversité spectrale, restent un challenge ob- servationnel.Les émissions atomiques aurorales sont bien documentées, mais ce n’est pas toujours le cas des émissions moléculaires, qui sont pourtant une source d’information potentielle sur les précipitations énergétiques prove- nant de la magnétosphère. C’est dans ce contexte que se place la définition de la mission du nanosatellite ATISE (Auroral Thermospheric and Ionosphe- ric Spectrometer Experiment), développé au Centre Spatial Universitaire de Grenoble. Il aura pour but l’observation de la haute atmosphère terrestre via l’acquisition de spectres dans le proche UV et le visible.Le diazote N2 et son ion N2+ font partie des composés majoritaires de l’atmosphère, et sont donc un choix cohérent afin de définir l’observabilité des émissions moléculaires. Le monoxyde d’azote NO est une espèce mino- ritaire dans la thermosphère, mais va avoir un rôle clé dans la destruction d’ozone stratosphérique, et donc dans la problématique du dérèglement climatique.Les émissions de ces composés, et notamment leurs profils verticaux ainsi que intensités ont été étudiées grâce au modèle TRANS, qui résout l’équation de Boltzmann pour le transport d’électrons. Ceci nous a aidé à caractériser les besoins scientifiques de la mission ATISE. Dans un second temps, l’analyse des résultats du démonstrateur-sol de ce nanosatellite a montré le potentiel de cette mission, bien que certaines spécifications ne soient pas encore atteintes. Enfin, toujours dans cette logique de recherche de nouvelles quantités observables pour la météorologie de l’espace, une dernière partie abordera la polarisation de la lumière aurorale, avec l’étude de la bande à 427,8 nm de N2+ . / Space weather is the study of the Solar activity’s impact on Earth’s space environment. This is relevant as it may have serious consequences over modern technology, such as high-voltage power lines grids or telecommu- nication systems via satellites. Solar activity is also the phenomenon that causes the aurorae, which can be seen in Earth’s upper atmosphere, at the poles, at the base of magnetic field lines. Due to this aurorae may be used as a proxy for the study of Solar particles trapped in Earth’s magnetic field.Auroral emissions are complex, as they are spread over various altitudes and wide spectral ranges. Therefore, they remain an observational chal- lenge.Emissions from atomic lines transitions in aurorae are well documented and understood, but this is not always the case for molecular emissions. These are a potential source of information on energetic inputs from the magnetosphere. This is the context in which the ATISE (Auroral Thermo- spheric and Ionospheric Spectrometer Experiment) nanosatellite was designed in the Grenoble University Space Center. Its purpose will be to observe Earth’s upper atmosphere through the acquisition of spectra in near-UV and visible domains.Dinitrogen N2 and its ion N2+ are major components of Earth’s atmos- phere at larges altitudes, and therefore a logical choice in order to define molecular emission observability. On the other hand, nitrogen monoxide NO is a minor component in the thermosphere, but has a key role in stra- tospheric ozone destruction, and therefore has important consequences on the climate.Auroral emissions, and more particularly their vertical profiles and in- tensities were studied with the TRANS model, which solves the Boltzmann equation for electron transport in the atmosphere. We used these results to define the scientific requisites for the ATISE mission. In a second phase, we tested and analyzed the results of a ground demonstrator of the instru- mentation that will be found in the nanosatellite. It showed great potential, despite the fact that part of the specifications are not yet fulfilled. Finally, still looking for new observables quantities for space weather, we studied the polarisation of auroral light, with a focus on the 427,8 nm band of N2+.

The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September 2002. The electrodynamics study utilized a two-dimensional flux tube integrated model in center dipole coordinates, which is derived in this work. This case study examined the relative influence of the zonal wind, meridional wind, vertical wind, temperature, and density perturbations of the gravity wave. It further looked at the angle of the wave front to the field line flux tube, the most influential height of the perturbation, and the difference between planar and thunderstorm source gravity waves with cylindrical symmetry. The results indicate that, of the five perturbation components studied, the zonal wind is the most important mechanism to seed the Rayleigh-Taylor instability needed to develop plasma plumes. It also shows that the bottomside of the F-region is the most important region to perturb, but a substantial E-region influence is also seen. Furthermore, a wave front with a small angle from the field line is necessary, but the shape of the wave front is not critical in the gravity wave is well developed before nightfall. Preliminary results from the three-dimensional model indicate that the equipotential field line assumption of the two-dimensional model is not valid below 100 km and possibly higher. Future work with this model should attempt to examine more of the differences with the two-dimensional model in the electric fields and currents produced as well as with the plasma drifts that lead to plume development.

The chemical reaction of the first excited electronic state of molecular nitrogen, N₂(A), with ground state atomic oxygen is an important contributor to thermospheric nitric oxide (NO).  The importance is assessed by including this reaction in a one-dimensional photochemical model.  The method is to scale the photoelectron impact ionization rate of molecular nitrogen by a Gaussian centered near 100 km. Large uncertainties remain in the temperature dependence and branching ratios of many reactions important to NO production and loss. Similarly large uncertainties are present in the solar soft x-ray irradiance, known to be the fundamental driver of the low-latitude NO.  To illustrate, it is shown that the equatorial, midday NO density measured by the Student Nitric Oxide Explorer (SNOE) satellite near the Solar Cycle 23 maximum can be recovered by the model to within the 20% measurement uncertainties using two rather different but equally reasonable chemical schemes, each with their own solar soft-xray irradiance parameterizations.  Including the N₂(A) changes the NO production rate by an average of 11%, but the NO density changes by a much larger 44%.  This is explained by tracing the direct, indirect, and catalytic contributions of N₂(A) to NO, finding them to contribute 40%, 33%, and 27% respectively. The contribution of N₂(A) relative to the total NO production and loss is assessed by tracing both back to their origins in the primary photoabsorption and photoelectron impact processes.  The photoelectron impact ionization of N₂ is shown to be the main driver of the midday NO production while the photoelectron impact dissociation of N₂ is the main NO destroyer.  The net photoelectron impact excitation rate of N₂, which is responsible for the N₂(A) production, is larger than the ionization and dissociation rates and thus potentially very important.   Although the conservative assumptions regarding the level-specific NO yield from the N₂(A)+O reaction results in N₂(A) being a somewhat minor contributor, N₂(A) production is found to be the most efficient producer of NO among the thermospheric energy deposition processes. / Ph. D.

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