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Reconstruction of fluid flow fields from data using Gaussian process regression with physics-informed kernels
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Numerical and Experimental Studies on Rotating Detonation Engines in ONERA-Pprime Collaboration
No full textInternational audienceThis study addresses the problematics of improving operating characteristics of a rotating detonation combustor (RDC) by means of injector optimisation. An injector concept with partial premixing of propellants in a small prechamber was developed and optimised at ONERA using numerical simulations. It was realised as the ITEM injector for a laboratory-scale RDC tested at the GAP facility of Pprime Institute, together with a commonly used injector design. The obtained results show superior detonation characteristics with the partially-premixed injection. The annular gap width is another important factor for detonation wave stability. Numerical simulations with the CEDRE code of ONERA demonstrate a fairly good agreement with the experimental results regarding detonation propagation characteristics and the visualised wave structure. The simulation results confirm good mixing ahead of the detonation front and low deflagration losses
Experimental and CFD Study of a Sub-scale Rotating Detonation Combustor Fed with Gaseous H₂−O₂
No full textInternational audienceUnderstanding the physical phenomena in a Rotating Detonation Engine combustor is essential for its practical application. Sub-scale Rotating Detonation Combustor testing enables extensive investigation under diverse conditions, clarifying the factors that influence detonation characteristics. Numerical simulations further enhance the comprehension of the combustor dynamics by revealing the intricate interactions from mixture formation to detonation, with a consensus highlighting mixture formation as key to stable, efficient detonation. A collaboration between ONERA and DLR is studying a subscale RDE combustor fed with gaseous H₂−O₂ . DLR manufactured and tested the combustor at the Lampoldshausen Centre, yielding data on injection parameters and detonation characteristics (wave number, propagation direction, and velocity). ONERA employs its CFD code CEDRE in an LES approach, modeling the entire chamber with the injector to capture the unsteady effects of periodic detonations on injection and mixing. This article presents experimental and numerical results for some selected cases, illustrating the alignment between both methods and offering insights into the mechanisms driving specific detonation regimes, particularly focusing on fresh mixture formation and conditions in the refill region
Campagne d'essai de caractérisation du décrochage sur une aile générique à flèche variable
No full textInternational audienceAircraft wing stall is a highly complex phenomenon as several mechanisms interact depending on global and local flow characteristics. Recent developments in numerical methods and aerodynamic modeling make possible the vision of an accurate prediction of stall in the near future. In order to reach this objective, there is a need for a high-quality experimental database for validation, including surface and flowfield measurements. To that purpose, a generic test model was specifically designed and built to provide force balance metrics as well as steady and unsteady pressure signals. In particular, the model takes into account forward, backward, and zero sweep angles while adding high-lift devices in order to modify the stall mechanism on the wing. The model was then tested at the ONERA-F2 wind tunnel, and experimental results validate the model’s intended stall characteristics and provide the needed flow data for future numerical validations. This paper describes the different design choices, the measurement techniques considered for this test campaign, and the first results obtained validating the stall processes expected for the different designed configurations.Le décrochage des ailes d'avion est un phénomène compexe au cours duquel différent mécanismes interagissent simultanément, chacun dépendant des caractéristiques locales de l´écoulement.Cependant, le développement des méthodes numériques et de modélisation permettent d'envisager une prévision précise du décrochage dans un avenir proche. Pour ce faire, il est nécessaire de se baser sur des bases de données expérimentales précises, considérant des mesures pariétales ou de champ. À cette fin, une maquette générique a été définie, comportant un grand nombre de prises de pression statiques et instationnaires. Cette maquette comporte une voilure à flèche variable, et peut être équipée de volets de bord de fuite ou d'un bec de bord d'attaque pour contrôler le type de décrochage désiré. Cette maquette a été testée dans la soufflerie F2 de l'ONERA et les essais ont permis de valider les différents designs associés à un type de décrochage. Cet article présente les différentes étapes de définition de la maquette ainsi que les techniques de mesure employées lors de cette campagne
Agency and perception: how action-based and externally cued predictions influence visual perceptual precision
No full textInternational audienceThe influence of action-based predictions on perception is fundamental, particularly for understanding the sense of agency, i.e., the subjective experience of control over one’s actions and their outcomes. While the literature reports mixed results, such as sensory attenuation or enhancement, the current research aims to contribute to our understanding of how actions and predictions influence visual perception through two experiments. In Experiment 1, participants viewed a grating and were asked to reproduce its orientation. Before the grating onset, different cues allowed them to predict its global orientation based on their own action (free-choice or forced-choice conditions) or an external cue (passive predicted condition), while in a control condition (passive neutral), no prediction was possible. Results revealed that perceptual precision in the reproduction task improved in both the free-choice and externally cued predictions compared to the passive neutral condition, whereas forced-choice predictions provided no such benefit. Experiment 2 investigated whether participants relied more on their predictions when the stimulus was harder to perceive. This was tested by examining the impact of free-choice action-based predictions under two levels of stimulus ambiguity within the same reproduction task. Results showed enhanced perceptual precision in the predicted condition compared to the unpredicted condition, regardless of task difficulty. Findings suggest that both cue based and action-based predictions can improve perceptual precision, but crucially, only when action are freely chosen. A lack of intentionality on action-based predictions may reduce attentional allocation to sensory action-effects, potentially limiting the benefits of sensory predictions for perception
Suivi de l'élaboration des composites thermoplastiques par Fibres Optiques à Réseaux de Bragg
No full textTo meet the economic and environmental challenges faced by the aerospace industry, there is a growing shift toward recyclable thermoplastic composites, which are easier to assemble and more resistant to thermomechanical loads than thermosetting composites. Out-of-autoclave processes, such as vacuum bag only (VBO) consolidation, are being explored to reduce costs, although certain manufacturing defects, such as poor interlaminar consolidation remain difficult to predict. This thesis proposes an in situ monitoring approach for the VBO process applied to thermoplastic composites with an LM-PAEK matrix reinforced with carbon fibers (CF/LM-PAEK), using embedded Fibre Bragg Grating (FBG) optical sensors. The material was first characterized, then thermomechanical tests were conducted to calibrate the FBG sensors in temperature and strain under conditions close to those of the manufacturing process. Real-time monitoring of the FBG spectrum enables the identification of matrix phase transitions, as well as the tracking of strain evolution and thermal expansion behavior under process conditions. The evolution of typical defects, such as poor interlaminar consolidation or an artificial gap, was successfully tracked throughout the cycle using FBG sensors. This work demonstrates the effectiveness of embedded FBG sensors for process monitoring and provides new insights into the consolidation mechanisms of thermoplastic composites.Pour répondre aux contraintes économiques et environnementales, l’industrie aéronautique s’oriente vers des composites thermoplastiques recyclables, plus faciles à assembler et plus résistants aux chocs thermomécaniques que les composites thermodurcissables. Des procédés hors autoclave, tels que la consolidation sous bâche à vide (VBO), sont explorés pour réduire les coûts, bien que certains défauts de fabrication, comme la mauvaise consolidation interpli, restent difficiles à maîtriser. Cette thèse propose une approche de suivi in situ du procédé VBO appliquée à des composites thermoplastiques à matrice LM-PAEK renforcée par des fibres de carbone, à l’aide de capteurs Fibres Optiques à Réseaux de Bragg (FBG) intégrés. Après une caractérisation préalable du matériau, une calibration des capteurs FBG en température et en déformation, dans ces conditions proches du procédé de consolidation, a été effectuée. Ces capteurs ont ensuite été intégrés dans le matériau pour en suivre l’élaboration : les transitions de phase de la matrice ont ainsi pu être identifiées et le coefficient de dilatation thermique (CTE) a été estimé. En outre, l’analyse de la réponse des FBG intégrés a permis de détecter l’apparition de défauts de consolidation interpli et de gaps artificiels et d’en surveiller l’évolution. Ces résultats ont confirmé l’intérêt des capteurs FBG pour un suivi du procédé et une meilleure compréhension des mécanismes de consolidation des composites thermoplastiques
Coupled simulations of radiative transfer and nonequilibrium flow in high altitude rocket plumes
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Diffusion in the TiN and Ti2N alloys: The case of N, Ti, and O
No full textInternational audienceIn this study, we investigate the self-diffusion of nitrogen (N) and titanium (Ti), as well as the diffusion of oxygen (O), within the δ-TiN and ϵ-Ti 2 N anti-rutile phases. Our approach combines density functional theory (DFT) calculations, to analyse the fundamental diffusion processes of these species with the KineCluE code to calculate the diffusion coefficients. We first identify the dominant defects in these systems, including titanium and nitrogen vacancies, as well as interstitial sites. In particular, oxygen shows a similar diffusion behaviour to that of nitrogen in these structures: coupling interstitial and vacancy diffusion mechanism. Atomic-scale analysis reveals that the diffusion pathways for nitrogen and titanium are decoupled, highlighting the unique dynamics within the NaCl-type lattice structure. Our calculations of the diffusion coefficients for nitrogen and titanium reveal significant asymmetries influenced by the alloy stoichiometry. The relatively low concentration of titanium vacancies, compared to the higher concentration of nitrogen vacancies, results in pronounced differences in the diffusion rates of the two elements. Finally, we investigate how diffusion mechanisms vary as a function of stoichiometry, providing new insights into the diffusion behaviour of nitrogen, titanium, and oxygen in key titanium nitride compounds. This work deepens our understanding of atomic-scale diffusion in these technologically important materials
3D finite-element mesh for modeling large-scale surface deformation induced by subduction megathrust earthquakes: Application to Chile
No full textInternational audienceMegaearthquakes (Mw > 8) cause continental-scale, long-lasting surface deformation, mainly due to viscoelastic relaxation of the asthenosphere. To investigate the links between this deformation and the slip history along subduction interfaces—including earthquakes, postseismic slip, and interseismic coupling—large 3D spherical finite-element meshes are required. This technical report introduces the various steps to build Chile_Mesh_v1.0, a customizable mesh for the Chilean subduction zone, designed as a robust platform for testing various viscoelastic rheologies. It spans ~8500 km in longitude, ~7300 km in latitude, encompassing the entire South American plate, and from the surface to 2900 km depth. Special care was taken to reproduce the complex slab geometry, especially in flat-slab regions such as the Pampean and Peruvian segments, following the Slab2 model. We show that accurately modeling both coseismic and postseismic deformation over large scales requires realistic meshed domains, extending down to the Core-Mantle boundary and thousands of kilometers from the trench. In some cases, depth-reduced meshes can be used to model viscoelastic postseismic deformation, but they fail to simultaneously capture coseismic deformation accurately. We hope this open-access mesh proves valuable for researchers studying subduction dynamics in Chile and supports the development of similar models for other regions
Stratégie d'intégration de batteries solides au sein de structures composites aéronautiques
No full textInternational audienceStratégie d'intégration de batteries solides au sein de structures composites aéronautique