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Analyse de l'Impact des Sillages Instationnaires et de la Cavité avec Débit de Purge sur l'Aérodynamique d'une Turbine Basse Pression Rapide
No full textInternational audienc
Maximisation of Lift-to-Drag Ratio for VLEO Platforms using Free-Form Deformation Techniques
No full textInternational audienceThe present work introduces a novel approach to optimise the shape of platforms operating in Very Low Earth Orbit (VLEO) by maximising their Lift-to-Drag ratio. VLEO platforms encounter significant atmospheric drag, posing challenges for long-duration missions. However, this residual atmosphere can also be harnessed to generate beneficial aerodynamic forces, offering a potential strategy to reduce the costs of orbital manoeuvres. To this end, the presented method leverages Free-Form Deformation (FFD) techniques to simultaneously minimise drag and maximise lift through the use of an aerodynamic evaluation tool tailored for free molecular flow. Central to this approach is a custom-developed shape generator, which converts parametric geometries into 3D meshes, enabling efficient exploration of various configurations. A first test case is conducted for drag reduction under volume and bounding box constraints to validate the optimisation framework, allowing the algorithm to explore optimal shapes within defined physical limits. The results are analysed and benchmarked against previous studies, demonstrating notable potential for improving aerodynamic performance. Subsequently, we extend the same FFD-driven optimisation by incorporating lift in the objective function. This second test case explores the potential of exploiting non-conventional geometries in VLEO environments, where the trade-offs between lift generation and drag reduction are crucial for mission efficiency. Preliminary results demonstrate the effectiveness of the proposed optimisation strategy in refining vehicle configurations for enhanced aerodynamic performance. The findings are anticipated to offer valuable insights into the design of future VLEO platforms, potentially increasing mission lifetimes and reducing fuel requirements through more efficient aerodynamic designs
Activated Diffusion of 1D J-Aggregates in Boron Nitride Nanotubes by Curvature Patterning
No full textInternational audienc
Dynamics and robust control of a space manipulator system servicing a satellite with flexible appendages
No full textInternational audienceSpace Manipulator Systems (SMS) are becoming pivotal in space exploitation and exploration, offering a versatile range of solutions from space debris capture to structure assembly. However, recent missions involving manipulators aboard satellites and space structures must contend with lightweight and large elements that exhibit flexible behaviors. Despite the challenges posed by flexible elements in their surroundings, enhancing the autonomy of SMS remains crucial to ensure their viability as solutions. For the pre-design of the SMS, path-planning applications, or controller design, there is a necessity for methods to assess the couplings between the manipulator, the SMS platform, and any flexible elements moved by a manipulator or attached to the platform. Moreover, recently proposed control strategies have demonstrated a keen interest in developing model-based controllers, which advantageously provide an efficient utilization of actuators and mitigation of internal disturbances within the system. This paper initially presents, for control purposes, the derivation of the kinematics and dynamics of a free-floating Space Manipulator System (SMS) with a flexible body at the end of a kinematic chain, employing a Lagrangian formalism. Subsequently, a robust joint-space control law is designed for the On-Orbit Servicing (OOS) of a satellite with flexible appendages. The control structure consists of Nonlinear Dynamic Inversion (NDI) for system linearization and decoupling. A structured H ∞ controller synthesis is developed to provide robustness against flexible disturbances, model uncertainties, and sensor noise. To evaluate the effectiveness of this control strategy, it is implemented on a real-time simulation platform that ensures tight and high-fidelity space robot dynamics and flexible structures. This platform incorporates visual environment models and virtual sensors to provide an accurate representation of real-world conditions. The considered use-case involves the servicing of a satellite equipped with a flexible solar array using a free-floating dual-arm SMS with flexible appendages
Numerical simulation of a high-pressure hydrogen-air combustion system for aircraft propulsion; comparison to experimental results
No full textInternational audienceGrowing environmental concerns have rekindled interest in hydrogen as a carbon-free combustion fuel for civil aviation. Present simulation work studies a swirl burner operated with hydrogen, tested on a high-pressure, high-temperature optical test bench. The burner involves coaxial injection of preheated air and pure hydrogen. Large-Eddy Simulation (LES) is performed for three stabilized operating conditions up to 13 bar. An 11-species reaction mechanism for hydrogen-air combustion is used. Simulation results are validated against optical measurements and an analysis of the phenomena involved is carried out
Development of an on-chip hyperspectral camera based on a 3D photonic integrated circuit (Conference Presentation)
No full textInternational audienceHyperspectral cameras collect spectral information for each pixel of their field of view. Such cameras extract more information about the scene than ordinary cameras. For field applications, they need to be SWaP compatible, meaning they have to be compact, light and have a reduced power consumption. They also have to be radiometrically and spectrally stable to produce reliable results. During the talk, we will present a new concept of a hyperspectral camera based on a three-dimensional Photonic Integrated Circuit (3D PIC) written using an ultrafast laser. By putting the 3D PIC input at the image plane of an optical system and the 3D PIC output before a focal plane array, we will add spectroscopy functionalities to the traditional imaging system. We will also present our latest laboratory results to reach the 3D PIC-based camera such as waveguides at several depths, straight and curved waveguides and integrated beam splitters. This includes numerical model and laboratory characterizations
Hauteur du panache volcanique lors de l'éruption de la Tajogaite (La Palma) de 2021, mesurée par deux méthodes de surveillance complémentaires : Implications pour les estimations des émissions massiques de SO2 par satellite
No full textInternational audienceVolcanic emissions from the Tajogaite volcano, located on the Cumbre Vieja edifice on the island of La Palma (Canary Islands, Spain), caused significant public health and aviation disruptions throughout the volcanic event (19 September – 13 December 2021, officially declared over on 25 December). The Instituto Geográfico Nacional (IGN), the authority responsible for volcano surveillance in Spain, implemented extensive operational monitoring to track volcanic activity and to provide a robust estimation of the volcanic plume height using a video-surveillance network. In parallel, the State Meteorological Agency of Spain (AEMET), in collaboration with other members of ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) in Spain, in collaboration with other institutions, carried out an unprecedented instrumental deployment to assess the atmospheric composition impacts of this volcanic event. This effort included a network of aerosol profilers surrounding the volcano. A total of four profiling instruments were installed on La Palma: one MPL-4B lidar and three ceilometers. Additionally, a pre-existing Raman lidar on the island contributed valuable data to this study. In this study, the eruptive process was characterised in terms of the altitude of the dispersive volcanic plume (hd), measured by both IGN and AEMET-ACTRIS, and the altitude of the eruptive column (hec), measured by IGN. Modulating factors such as seismicity and meteorological conditions were also analysed. The consistency between the two independent and complementary datasets (hd,IGN and hd,AEMET) was assessed throughout the eruption (mean difference of 258.6 m). Our results confirmed the existence of three distinct eruptive phases, encompassing a range of styles from Strombolian explosive to effusive activity. While these phases have been characterised in previous studies, the results of the present work provide complementary information and novel insights from a different scientific perspective, which may be of use in future volcanic crises and will be applied to operational surveillance during such events. A subsequent comparison of hd,AEMET with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol layer height product (ALHCALIOP) revealed a systematic underestimation by the satellite product, with a mean difference of 392.2 m. Finally, the impact of using hec in estimating SO2 emissions from the NASA MSVOLSO2L4 satellite-based product was evaluated. When a fixed (standard) plume altitude of 8 km was used instead of the observed hec, the total SO2 mass was significantly underestimated by an average of 56.2 %, and by up to 84.7 %. These findings underscore the importance of accurately determining the volcanic plume height when deriving SO2 emissions from satellite data.Les émissions volcaniques du volcan Tajogaite, situé sur l'édifice Cumbre Vieja sur l'île de La Palma (îles Canaries, Espagne), ont provoqué d'importantes perturbations pour la santé publique et l'aviation tout au long de l'événement volcanique (du 19 septembre au 13 décembre 2021, officiellement déclaré terminé le 25 décembre). L'Instituto Geográfico Nacional (IGN), l'autorité responsable de la surveillance des volcans en Espagne, a mis en œuvre une surveillance scientifique approfondie pour suivre l'activité volcanique et fournir une estimation fiable de la hauteur du panache volcanique à l'aide d'un réseau de vidéosurveillance. En parallèle, l'Agence météorologique nationale espagnole (AEMET), en collaboration avec d'autres membres de l'ACTRIS (Infrastructure de recherche sur les aérosols, les nuages et les gaz traces) en Espagne, en collaboration avec d'autres institutions, a réalisé un déploiement instrumental sans précédent pour évaluer les impacts de cet événement rare sur la composition atmosphérique. Cet effort comprenait un réseau de profileurs d'aérosols entourant le volcan. Au total, quatre instruments de profilage ont été installés sur La Palma : un lidar MPL-4B et trois célomètres. De plus, un lidar Raman préexistant sur l'île a fourni des données précieuses à cette étude
Coupled simulations of radiative transfer and nonequilibrium flow in high altitude rocket plumes
No full textInternational audienc
Gaps in stellar streams as a result of globular cluster flybys. The case of Palomar 5
No full textInternational audienceContext. Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. The literature commonly interprets the presence of underdensity regions, or gaps, along these streams as being due to the close passage of dark matter subhalos. Aims. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream generated by a cluster with characteristics (mass, size, and orbit) similar to those of Palomar 5, a well-known globular cluster in the Galactic halo that has particularly long tidal tails. Methods. For this purpose, we used a particle-test code to simulate the formation and evolution of the stream when subjected to the Galaxy's gravitational field plus its whole system of globular clusters. Results. Our study shows that such a stream can be strongly perturbed by the close passage of other clusters, in particular NGC 2808, NGC 7078, and NGC 104, and that these perturbations induce the formation of gaps in the tails. Conclusions. The results of this work show that globular clusters can induce gaps in cold streams-just as it has been demonstrated in the literature for that other baryonic components, such as giant molecular clouds and the Galactic bar. Therefore, a future work that attempts to infer the dark matter subhalo distribution from stellar stream gaps must include the contributions from globular clusters.</div
Étude et développement d'un lidar UV à détection directe pour la mesure du vent 3D dans le cadre des futurs avions ayant des ailes à grand allongement
No full textThe development of a direct-detection UV lidar architecture for wind measurement upstream of low-consumption aircraft is presented. These aircraft will be equipped with larger wingspans to improve lift but will be more sensitive to turbulence. To reduce the stress caused by wind turbulence on the wings, a load control system is required, which relies on upstream wind measurements to operate at full potential. Direct-detection lidar enables such measurements by deducing the wind velocity projected along the laser axis from the frequency shift induced by the Doppler effect on the backscattered wave, caused by the movement of particles and molecules. Since molecules are present at all altitudes, direct-detection lidar can measure wind 100% of the time upstream of the aircraft. Because molecular backscattering is proportional to 1/λ^4, where λ is the wavelength, the backscattered signal comes from a UV laser to increase the amount of received signal. To ensure insensitivity to atmospheric parameters, the lidar uses a quadrature Mach-Zehnder interferometer as a spectrum analyzer. The lidar architecture was optimized using a simulator to minimize the standard deviation of the projected velocity estimate. The development and experimental characterization of the interferometer are presented. Additionally, the study of 3D wind reconstruction in turbulence, based on lidar measurements, is detailed.Le développement d'une architecture lidar UV à détection directe pour la mesure de vent en amont des avions basses consommations est présenté. Ces avions seront équipés d'ailes de plus grande envergure pour améliorer la portance, mais seront plus sensibles aux turbulences. Pour réduire les contraintes induites par les turbulences de vent sur l'aile, un système de contrôle de charge est nécessaire, qui requiert la mesure de vent en amont de l'avion pour être exploité à son plein potentiel. Le lidar à détection directe permet de réaliser cette mesure, en déduisant la vitesse du vent projetée sur l'axe du laser à partir du décalage en fréquence induit par effet Doppler sur l'onde rétrodiffusée, dû au mouvement des particules et molécules. Les molécules étant présentes à toute altitude, le lidar à détection directe est capable de mesurer le vent 100 % du temps en amont de l'avion. La rétrodiffusion moléculaire étant proportionnelle à 1/λ^4, où λ est la longueur d'onde, le signal rétrodiffusé provient d'un laser UV pour augmenter la quantité de signal reçu. Pour être insensible aux paramètres atmosphériques, le lidar utilise un interféromètre quadri Mach-Zehnder comme analyseur de spectre. L'architecture lidar a été optimisée grâce à un simulateur pour minimiser l'écart-type d'estimation de la vitesse projetée. Le développement ainsi que les caractérisations expérimentales de l'interféromètre sont présentés. En parallèle, l'étude de la reconstruction du vent 3D dans une turbulence, à partir des mesures lidar, est détaillée