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This paper is a short retrospective review of the predictive methods of turbulent flows in Computational Fluid Dynamics over the last 50 years since the first development of computers. The different schools of turbulence modeling are presented with the aim to guide both users and researchers involved in numerical simulation of turbulent flows.; Cet article est une courte rétrospective de synthèse des méthodes prédictibles des écoulements turbulents.Des simulations des écoulements sur ces 50 dernières années depuis les premiers développement des ordinateurs.Les différentes écoles de la modélisation des turbulences sont présentées dans le but de guider à la fois les utilisateurs et les chercheurs impliqués en simulation numérique des écoulements turbulents.

Aviation NOx emissions have not only an impact on global climate by changing ozone and methane levels but also contribute to deteriorate local air quality. In order to properly assess the co-benefit with air quality improvement and the trade-off with the climate change associated with CO2, it appears essential to better quantify the climate impact of aircraft NOx emissions. A new version of the LMDZ-INCA global model, including both tropospheric and stratospheric chemistry and the sulfate-nitrate-ammonium cycle, is applied to re-evaluate the impact of aircraft NOx and aerosol emissions on climate. The results confirm that the efficiency of NOx to produce ozone is very much dependent on the injection height. For the baseline simulation and reference scenario this efficiency is 6.6 TgO3/TgN. The efficiency increases with the background methane and NOx concentrations and with decreasing aircraft NOx emissions. The same findings translate to the associated ozone radiative forcing which exhibits a fairly constant value per ozone mass change of 3.4 mW/m2/TgO3. The methane lifetime variation is less sensitive to the aircraft NOx emission location than the ozone change. The change in CH4 mixing ratio itself represents 75 % of the total methane forcing. The indirect changes through long-term tropospheric ozone, stratospheric water vapour and methane oxidation to CO2 contribute for 19 %, 4 % and 1 %, respectively. The net NOx radiative forcing (O3 + CH4) is largely affected by the revised CH4 radiative forcing formula which increases the total CH4 negative forcing by 15 %. As a consequence, the ozone positive forcing and the methane negative forcing largely offset each other resulting in a slightly positive forcing for the present-day. However, in the future, the net forcing turns to negative due essentially to higher methane background concentrations. Additional radiative forcings involving particle formation arise from aircraft NOx emissions since the increased OH concentrations are responsible for an enhanced conversion of SO2 to sulfate particles. Aircraft NOx emissions also increase the formation of nitrate particles in the lower troposphere. However, in the upper-troposphere, increased sulfate concentrations favor the titration of ammonia leading to lower ammonium nitrate concentrations. The total forcing from sulfate and nitrate aerosols associated with NOx emissions is negative and is estimated to -3.0 mW/m2/TgN for the present-day. When these aerosol radiative forcings are considered, the total NOx forcing turns from a positive value to a negative value even for present-day conditions. Hence, total radiative forcing from aircraft emissions associated with changes in atmospheric chemistry and direct aerosols forcings is negative for both present-day and future (2050) conditions. NOx emissions only cause a negative forcing representing about 45 % of the total forcing. The negative forcing associated with sulfates largely dominates the effect of the other particles. The sulfate direct radiative forcing is estimated to be associated for about 50 % with the direct SO2 and SO4 aircraft emissions and for about 50 % with the increased conversion of SO2 to SO4 at higher OH concentrations, and hence related to the NOx emissions. The net effect of decreasing (resp. increasing) the flight altitude by 2000 ft (about 610 m) is to increase (resp. decrease) the total negative forcing by 57 % (resp. 65 %). The variation of the total forcing with flight altitude is dominated by the high sensitivity of the ozone positive forcing to the altitude of the perturbation. Several mitigation options involving flight aircraft operation and cruise altitude changes, traffic growth, engine technology, and fuel type, exist to reduce the climate impact of aircraft NOx emissions. However, the climate forcing of aircraft NOx emissions is likely to be small or even switch to negative (cooling) depending on atmospheric NOx or CH4 future background concentrations or when the NOx impact on sulfate and nitrate particles is considered. There remain large uncertainties on the NOx net impact on climate effect calculation. Nevertheless, the results suggest that reducing aircraft NOx emissions is primarily beneficial for improving air quality. For climate consideration, one option to reduce uncertainties in mitigation strategies might be to prioritize the reduction of CO2 aircraft emissions which have a well-established and long-term impact on climate, however this reduces the overall mitigation potential.

International audience; Comme toute technologie le radar évolue et fait face à de nombreuses problématiques (management de spectre, traitement du clutter, amélioration de la résolution, ...). Cela conduit à la création et l'optimisation de nouvelles formes d'ondes conjointement à leur traitement. Pour y parvenir, nous avons orienté notre étude sur des signaux bio-inspirés de ceux des chauvessouris et observé les avantages potentiels à utiliser de telles formes d'ondes. Cet article présente une comparaison entre des formes d'ondes dites classiques en radar et une autre bio-inspirée en analysant notamment leurs réponses à un traitement usuel. La modélisation de cette forme d'onde bio-inspirée permet de comparer plusieurs stratégies de modulation fréquentielle au sein d'une impulsion. Les bornes de Cramér-Rao sont calculées afin de quantifier les capacités d'estimation en retard et Doppler de chaque forme d'onde.

It is well known that acoustical factors explain only partly the human perception of aircraft noise. In order to truly understand annoyance ratings, acoustical and non-acoustical factors have to be taken into consideration, making it often complex to analyze studies that treat only one side of the issue. While field studies give a good insight of long-term annoyance in realistic living conditions, laboratory tests are commonly used as means to understand the impact of acoustic factors on noise annoyance and unpleasantness while usually smoothing inter individual differences. A French project (CIGALE) has set a goal of creating a frame of reference making it possible to include non-acoustical factors into laboratory studies. After an extensive field study and focus groups in the first part of the project resulting in six different profiles of residents, the second part comprises a vast laboratory test campaign in Toulouse and Paris region aiming at evaluating the impact of these profiles on the perception of two common acoustical factors in an ecological experimental setup. Overall more than 300 residents of the Toulouse Blagnac airport area and the Roissy Charles de Gaulle airport area participated in the CIGALE listening test. Participants were asked to read novels while seated in a listening room with a 3D audio simulation of an everyday soundscape. They were asked to rate their perception of four 15 minutes sequences randomly presented in which the number of aircraft flyovers and the maximum A-weighted sound level of each flyover were varied. Four different scales were used: task interference, mental effort, annoyance and comfort. The results support the hypothesis that profile type and noise sensitivity have an impact on annoyance ratings. The collected data also highlighted different response strategies regarding acoustical factors that need to be further investigated., Il est bien connu que les facteurs acoustiques n'expliquent qu'en partie la perception humaine du bruit des avions. Afin de bien comprendre une évaluation de gêne, les facteurs acoustiques et non acoustiques doivent être pris en compte, ce qui rend souvent complexe l'analyse d'études qui ne traitent qu'un aspect du problème. Alors que les études sur le terrain donnent un bon aperçu de la gêne à long terme dans des conditions de vie réalistes, les tests en laboratoire sont couramment utilisés pour comprendre l'impact des facteurs acoustiques sur la gêne et le désagrément liés au bruit, tout en atténuant généralement les différences interindividuelles. Un projet français (CIGALE) s'est fixé pour objectif de créer un référentiel permettant d'intégrer des facteurs non acoustiques dans les études en laboratoire. Après une vaste étude de terrain et des ateliers participatifs dans une première partie du projet aboutissant à six profils d'habitants différents, la seconde partie comprend une vaste campagne de tests en laboratoire à Toulouse et en région Parisienne visant à évaluer l'impact de ces profils sur la perception de deux facteurs acoustiques communs dans un montage expérimental écologique. Au total plus de 300 habitants de la région aéroportuaire de Toulouse Blagnac et de celle de Roissy Charles de Gaulle ont participé au test d'écoute CIGALE. Les participants ont été invités à lire des romans assis dans une salle d'écoute avec une simulation audio 3D d'un paysage sonore représentant une situation sonore rencontrée au quotidien. On leur a demandé d'évaluer leur perception de quatre séquences sonores de 15 minutes présentées au hasard dans lesquelles le nombre de survols d'aéronefs et le niveau sonore maximal de chaque survol étaient modifiés. Quatre échelles différentes ont été utilisées : l'interférence sur la tâche, l'effort mental, la gêne et le confort. Les résultats soutiennent l'hypothèse selon laquelle le type de profil et la sensibilité au bruit ont un impact sur les notations de gêne. Les données collectées ont également mis en évidence différentes stratégies de réponse concernant les facteurs acoustiques qui doivent être étudiées plus en détail.

International audience; The present work studies the mechanism of tonal slat noise generation in high-lift devices. Peaks in the emitted noise spectrum are observed for small-scale geometries with various slat configurations. They are attributed to a feedback mechanism in the slat cove similar to that in cavity flows. The objective of this study is to characterize the flow structures which are at the origin of this tonal noise, and future work may focus on investigating the effect of the flow parameters (Reynolds number, Mach number, angle of attack) on its generation. To this end, a 2-element airfoil composed of a slat and a main body is considered. This geometry is designed to isolate slat noise from other possible sources while providing a flow representative of a realistic 3-element airfoil near the slat. The coherent structures involved in the tonal noise are then identified from high-fidelity unsteady CFD data using Spectral Proper Orthogonal Decomposition (SPOD). The present work reveals that the obtained structures show good agreement with the recent paper of Himeno et al. (JFM 2021). In addition to the midrange frequencies, which are classically associated with the loop feedback mechanism, the analysis also reveals a high-frequency mode whose structure is concentrated in the wake of the upper slat trailing edge.; La présente activité étudie le mécanisme de génération de bruit de bec tonales dans les dispositifs hypersustentateurs. Des pics dans le spectre de bruit émis sont observés pour des géométries à petite échelle avec diverses configurations de becs. Ils sont attribués à un mécanisme de rétroaction dans la cavité similaire à celui des écoulements en cavité ouverte. L'objectif de cette étude est de caractériser les structures d'écoulement qui sont à l'origine de ce bruit tonal, et des travaux futurs pourraient se concentrer sur l'étude de l'effet des paramètres d'écoulement (nombre de Reynolds, nombre de Mach, angle d'attaque) sur sa génération. A cet effet, une voilure à 2 éléments composée d'un bec et d'un corps principal est considérée. Cette géométrie est conçue pour isoler le bruit du bec des autres sources possibles tout en fournissant un écoulement représentatif d'un profil aérodynamique réaliste à 3 éléments près du bec. Les structures cohérentes impliquées dans le bruit tonal sont ensuite identifiées à partir de données CFD instationnaires haute fidélité à l'aide de la décomposition spectrale en mode propre (SPOD). Les pics observées dans le spectre champ lointain sont également identifiées dans le spectre SPOD. Les structures de mode SPOD aux fréquences des raies montrent un bon accord avec le mécanisme de génération de bruit de bec identifié dans la littérature.

International audience; In the context of airplane structures monitoring, the performance of an embedded SHM system for composite material components is studied. The present article focuses on the influence of the PZT transducers integration on the Lamb waves it generates. First the article presents finite element modeling of Lamb waves generation in a carbon/epoxy plate, either with surface mounted or with embedded PZT transducer. Ultrasonic wavefield simulated in both configurations are compared. Experiments are also performed on composite laminates with embedded or surface mounted PZT. The out-of-plane displacement induced by PZT excitation on the plate surface is measured by Laser Doppler Vibrometry in both configurations. Out-of-plane displacements are compared together.

International audience; This work presents an actuator disk-like body force method designed for propeller modeling, which is based on a full coupling between Computational Fluid Dynamics (CFD) and Blade Element Theory (BET). An analysis is conducted on the model to identify best practices for source term distribution. It is found that the source term volume shape has no impact on propeller loads and flow field, and that the velocities used for the BET analysis at each radial section should be evaluated exactly where half the source terms have been distributed in the CFD domain. Four tip-loss corrections, including two from literature, are also analyzed and compared to lifting-line and CFD blade-resolved computations. The best practices and the most effective tip-loss correction lead to a final model that is evaluated for different pitch angles and incidence angles, on ONERA's HAD-1 three-bladed light propeller. The RANS/BET body force model predicts thrust within 3% for axial flow and 8% for cases with incidence. The same accuracy is obtained for wake prediction.; Ce travail présente une méthode de modélisation d’hélices par termes sources appelée RANS/BET. Elle est basée sur un couplage complet entre CFD et Blade Element Theory. Une analyse est menée sur le modèle afin d'identifier les meilleures pratiques pour la distribution des termes source. Les résultats montrent que la forme du volume dans lequel les termes sources sont répartis n’a pas d'impact sur les charges de l'hélice et sur les champs de vitesse dans le sillage, et que les vitesses utilisées pour l'analyse BET doivent être évaluées exactement là où la moitié des termes sources ont été distribués dans le domaine CFD. Quatre corrections de bout de pale, dont deux provenant de la littérature, sont également analysées et les résultats sont comparés à des calculs ligne-portante et CFD pales maillées. Le modèle est évalué pour différents angles de calage et d'incidence, sur l'hélice légère tripale ONERA HAD-1. Le modèle RANS/BET prédit la poussée hélice avec un écart de 3 % pour l'écoulement axial et de 8 % pour les cas avec incidence. La même précision est obtenue pour la prédiction des champs de vitesse du sillage.

International audience; Useful parameterisations of shapes for engineering models often climb from many tens to a few hundreds design variables, potentially jeopardising usual optimisation techniques. Surrogate models are intractable when parameter numbers exceed a few tens, and gradient descent through adjoint computation in high-dimension is threatened by potential multimodality. Dimension reduction addresses these problems nicely. This paper aims to improve upon the Active Subspaces dimension reduction method by applying a combination of active subspaces in subregions of the design space, where their use of the objective function’s gradients will exploit useful local information to discover specific trends instead of trying to identify global trends over an entire design space. The partitioning of the input space is done through Gaussian Mixture Model clustering, where the authors assume the distribution of the joint inputs/outputs to be a mixture of Gaussians. This GMM clustering is used to drive a Support Vector Machines (SVM) based supervised classifier. The SVC classifier’s margin (the maximal separation distance between points of different clusters) is chosen using cross validation in order to set an optimal width for the overlapping zones. The use of overlapping increases prediction accuracy at the boundaries between clusters, an improvement over recombination methods typically found in the literature. The local expert of choice is Kriging, in part due to its built-in variance prediction.

International audience; This paper presents a comparison among efficient techniques for uncertainty quantification on the RAE2822 airfoil whose shape is affected by uncertain geometrical parameters. Transonic conditions are considered with focus on estimating the statistics of the aerodynamic coefficients predicted by RANS simulations and using a far-field drag analysis of the computed flow field. Generalized polynomial chaos expansion with least-square approximation is employed for stochastic surrogate modelling. Two different kind of approaches enabling the high-dimensionality of the uncertainty space are investigated: 'compressed sensing' through Least Angle Regression and Basis Pursuit Denoising methods, and the 'gradient enhanced' formulation of the least-square approach exploiting the adjoint capabilities of modern CFD solvers.; Cet article presente une comparaison de différentes techniques efficaces de quantification d'incertitudes sur le profil RAE2822 en condition transsonique, dont la forme est affectée par des incertitudes géométriques. Le focus porte sur l'estimation des moments statistiques des coefficients aérodynamiques par simulation RANS suivie d'une décomposition de trainée champ lointain. Une expansion basée sur les polynomes du chaos construite par la méthode des moindres carrés est ensuite utilisée pour construire un meta-modèle. Deux approches differentes permettant de traiter la grande dimension de l'espace des paramètres incertains sont étudiées : 'compress sensing' avec les méhodes Least Angle Regression et Basis Pursuit Denoising, et une formulation 'gradient augmentée' de l'approche moindres carrés qui exploite les capacités adjointes des solveurs CFD modernes.

International audience; Integration of photonic structures in nanocrystal-based photodetectors has been demonstrated to improve device performances. Furthermore, bias-dependent photoresponse can be observed in such devices as a result of the interplay between hopping transport and inhomogeneous electromagnetic field. Here, we investigate the main physical concepts leading to a voltage-dependent photoresponse. We first bring evidence of bias-dependent carrier mobilities in a nanocrystal array over a wide range of temperatures. Then, we realize an infrared sensing device using HgTe nanocrystals, where the electrodes also play the role of a grating, inducing a spatially inhomogeneous absorption. The obtained device exhibits a significant bias-dependent photoresponse while possessing a competitive detection performance in the extended shortwave and mid-wave infrared, with detectivity reaching 7x10 10 Jones at 80 K and a fast response time of around 70 ns. This work provides the foundation for further advancements in nanocrystal-basedactive photonics devices.

The study of heat transport in porous media has recently attracted a lot of attention due to the wide range of industrial and geological applications, yet the impact of the structural heterogeneity of naturally occurring aquifers on their hydraulic and thermal properties is often disregarded. In that regard, a novel application of phosphor thermometry to porous media is proposed with the aim of examining under which conditions the validity of existing thermal transfer models in complex natural saturated porous media can be questioned. This experimental technique relies on monitoring the temperature-dependent luminescence properties of solid phosphor particles seeded into the fluid as tracers, using light sources and cameras. It offers the possibility of characterizing quantitatively the interaction between flow and heat transport processes at the pore scale in transparent analog porous media, with minimal interference and from spatially-resolved measurements, hereby overcoming the technical limitations of current experimental techniques, which are constrained to point temperature measurements.Here, as proof of concept, we present a demonstration experiment performed on a slow-moving flow in a synthetic porous medium with a heterogenous size distribution, and using YAG:Cr3+, a thermographic phosphor with a temperature sensitivity exceeding 0.3%/K [1]. The measurements are performed using a modulated light source and are recorded at a sampling rate of 1 kHz during continuous injection of an aqueous solution which is initially at a constant temperature, different from that of the resident solution. The results show the dynamics of the spatial temperature distribution in the porous medium with a precision of ±0.3°C.[1] J. L. Bonilla and B. Fond, "Phosphor thermometry using the phase-shift method: optimization and comparison with decay time method," 2022.

International audience; Flow control consists in modifying a flow natural state in order to converge towards another state which is considered as favorable, as drag or noise radiation might be reduced. In this paper, open-loop flow control experiments are carried out on a subsonic open-cavity flow. In the case of unstable flow control, the control focus is brought onto the flow fluctuations modifications rather than modification of the mean flow properties. Therefore, the forcing flexibility using arbitrary signals and the forcing linearity are essential for such flow control cases. In that sense, a linear array of Micro Magneto-Electro-Mechanical Systems actuators has been implemented to perform open-loop flow control experiments on an open-cavity. The actuators are able to generate both quasi-steady and pulsed jets with linear behavior. We proved the microvalves efficiency to damp the cavity oscillations. The quasi-steady jets reached a reduction of 20 dB in the cavity fundamental amplitude sound pressure level. Pulsed jets enabled an additional cavity tone amplitude reduction, which depends on the pulsating frequency and on the forcing amplitude. These results are a first step towards the implementation of the closed-loop control of the open-cavity flow.

International audience; The tip gap region of an axial compressor rotor is the source of complex flows inducing losses and stability issues. Recent works have proven the ability of blowing high-speed jets in the tip region to improve the surge margin of an axial compressor stage with a narrow tip gap configuration. Nevertheless, the tip gap size can evolve during the compressor lifetime, possibly affecting its performance and operability. The objective is to evaluate the performance of an active flow control system on a compressor with different tip gap sizes. The present work is based on the single stage compressor CME2 located at the Laboratory of Fluid Mechanics of Lille and equipped with actuators blowing at the rotor tip leading edge. Configurations with two different values of the tip gap to chord ratio (0.6% and 2.4%) have been experimentally tested. RANS simulations have also been performed. The effect of tip gap sizes and of the tip-blowing is evaluated on the flow topology and compressor performance.; La région du jeu en extrémité d'aubes de rotor de compresseur est la source d'écoulements complexes à l'origine de pertes et d'instabilités. De récents travaux ont montré la capacité de jet fluidiques haute-vitesse à améliorer la marge au pompage d'un compresseur axial monoétagé, avec un jeu réduit. Néanmoins, la taille de jeu évolue au cours de la vie du compresseur. ce qui affecte ses performances et son domaine d'opérabilité. L'objectif est d'évaluer la performance d'un dispositif de contrôle actif pour différentes tailles de jeu, sur le compresseur CME2. Ce travail est basé sur le banc d'essais localisé au Laboratoire de Mécanique des Fluides de Lille, et équipé d'actionneurs soufflant à l'amont du bord d'attaque, en tête de rotor. Deux tailles de jeu ont été évaluées expérimentalement (0,6% et 2,4%) ainsi que numériquement à l'aide de simulations RANS. L'effet de la taille de jeu et de l'injection est évalué en termes de topologie d'écoulement et de performances du compresseur.

International audience; For high dimensional spaces, a randomized Gram-Schmidt (RGS) algorithm is beneficial in computational costs as well as numerical stability. We apply this dimension reduction technique by random sketching to Krylov subspace methods, e.g. to the generalized minimal residual method (GMRES). We propose a flexible variant of GMRES with the randomized Gram-Schmidt based Arnoldi iteration to produce a set of basis vectors of the Krylov subspace. Even though the Krylov basis is no longer l2 orthonormal, its random projection onto the low dimensional space shows l 2 orthogonality. As a result, it is observed the numerical stability which turns out to be independent of the dimension of the problem even in extreme scale problems. On the other hand, as the Harmonic Ritz values are commonly used in GMRES with deflated restarting to improve convergence, we consider another deflation strategy, for instance disregarding the singular vectors associated with the smallest singular values. We thus introduce a new algorithm of the randomized flexible GMRES with singular value decomposition (SVD) based deflated restarting. At the end, we carry out numerical experiments in the context of compressible turbulent flow simulations. Our proposed approach exhibits a quite competitive numerical behaviour to existing methods while reducing computational costs.

International audience; This study presents simulations and experiments on the effect of porous bleed systems on a supersonic turbulent boundary layer at a Mach number of M=1.6. The results indicate a good fit between the RANS simulations and the experiments based on LDV, BOS, and pressure measurements. The numerical simulations well capture the overall flow topology. Both approaches show the same trend of fuller profiles with higher suction rates. The findings suggest that RANS simulations can be used to investigate the effect of bleed systems for different bleed parameters to improve bleed models. Overall, this study provides valuable insights into the working principle of bleed systems, which are crucial for designing and optimizing supersonic air intakes.

International audience; The International Civil Aviation Organization (ICAO) needs to define standards for the advent of this new generation of supersonic aircrafts. In this context, the SENECA EU H2020 project aims at quantifying the NO x , H 2 O and contrails climate effects from supersonic aviation. 3D RANS contrails simulations are performed during the jet phase with a realistic supersonic aircraft configuration. A crucial step of the contrail simulation process related to the grid mesh optimization is described and analysed in this paper.

International audience; This paper presents the aerodynamic performance study of an isolated ultra-high bypass ratio turbofan engine. The performance assessment methodology relies on an exergy balance, computed using the ONERA FFX software on the basis of RANS CFD solutions. The study first investigates aspects associated with the computational strategy used to simulate engines of this type. This concerns in particular a grid convergence study and a comparison of different types of modelisation methods for the fan and OGV, in terms of the exergy balance. At a second step, an exergy-balance-based analysis of the engine is carried out at different operating conditions. This analysis allows the evaluation of the system's overall performance, while at the same time providing a phenomenological decomposition of mechanical/thermocompressible exergy outflows and the characterization of exergy losses due to irreversible effects.; Ce papier présente l'étude de la performance aérodynamique d'un moteur de type turbofan à très haut taux de dilution (UHBR = ultra-high bypass ratio). La méthodologie d'évaluation de la performance repose sur un bilan d'exergie, calculé en utilisant le logiciel FFX de l'ONERA sur la base de solutions CFD RANS. L'analyse concerne tout d'abord des aspects associés à la stratégie numérique utilisée pour la simulation de ce type de moteurs. Cela concerne en particulier une étude de convergence en maillage et une comparaison de différents types de méthodes de modélisation pour le fan et l'OGV, en termes du bilan d'exergie. Dans un deuxième temps, une analyse du moteur par bilan d'exergie est effectuée à différents points de fonctionnement. Cette analyse permet l'évaluation de la performance globale du système, tout en fournissant une décomposition phénoménologique des flux sortants d'exergie mécanique/thermocompressible et la caractérisation des pertes d'exergie à cause des effets irréversibles.

The H2020 MINOTOR project focused on the study and the optimization of the ECRA thruster, an electric propulsion system for satellites. First, a 30 W prototype of this Electron Cyclotron Resonance Thruster (ECRT) is optimized. Then, a 200 W prototype is design based on these findings. The performances of both prototypes were assessed at two different facilities: at ONERA in France and at Justus Liebig University in Germany. Significant improvement of performances of both thrusters with the decrease of background pressure is presented. Total thrust efficiencies as high as 50% are measured at JLU, as well as erosion and lifetime assessment. The stability of the thruster for a constant point of operation was measured for one hundred hours of operation.

International audience; The MICROSCOPE mission tested the Weak Equivalence Principle (WEP) with an unprecedented precision of order 10−15, two orders of magnitude better than the previous best lab experiments. While the WEP, the cornerstone of General Relativity (GR), does not sway, the decade-long problems faced by fundamental physics stay still: how can we unify GR with the Standard Model, and how can we explain the acceleration of the cosmological expansion? As most beyond-GR models predict a violation of the WEP, albeit at an unknown level, it remains critical to even better test the WEP. In this paper, we review the MICROSCOPE mission, give its final constraint on the WEP, and build on its experimental limitations to show how we could improve them by a further two-order of magnitude in the precision of the test of the WEP.

Nanocrystals’ (NCs) band gap can be easily tuned over the infrared range, making them appealing for the design of cost-effective sensors. Though their growth has reached a high level of maturity, their doping remains a poorly controlled parameter, raising the need for post-synthesis tuning strategies. As a result, phototransistor device geometry offers an interesting alternative to photoconductors, allowing carrier density control. Phototransistors based on NCs that target integrated infrared sensing have to (i) be compatible with low-temperature operation, (ii) avoid liquid handling, and (iii) enable large carrier density tuning. These constraints drive the search for innovative gate technologies beyond traditional dielectric or conventional liquid and ion gel electrolytes. Here, we explore lithium-ion glass gating and apply it to channels made of HgTe narrow band gap NCs. We demonstrate that this all-solid gate strategy is compatible with large capacitance up to 2 µF·cm−2 and can be operated over a broad range of temperatures (130–300 K). Finally, we tackle an issue often faced by NC-based phototransistors:their low absorption; from a metallic grating structure, we combined two resonances and achieved high responsivity (10 A·W−1 or an external quantum efficiency of 500%) over a broadband spectral range.

Ice velocity observations available on-line or on-demand at intra-annual resolution still contain gaps, noise, and artifacts, especially in mountain areas. There is a need to fuse the available multi-temporal and multi-sensor velocity observations to be able to study intra-annual glacier dynamics. The proposed approach includes an inversion based on the temporal closure of displacement observation networks and a temporal interpolation. It reconstructs velocity time series between consecutive dates at a regular temporal sampling (called Regular Leap Frog (RLF) time series) inferred from all the velocity observations without a prori knowledge on the displacement behavior. The RLF time series can be reconstructed for different temporal sampling. Root Mean Square Error (RMSE) over stable areas and Velocity Vector Coherence (VVC) over fast moving areas are proposed to select a temporal sampling allowing a compromise between uncertainty and temporal resolution. This study focuses on the Fox glacier, in the Southern Alps of New Zealand. It shows that RMSE over stable areas is decreased from 78% for a temporal sampling of 5 days to 40% for a temporal sampling of 60 days. Thus, using this approach, we obtain a velocity time series with a complete temporal coverage and reduced uncertainty for a regular and optimal temporal sampling. The results highlight the large seasonal variability of the flow of Fox Glacier that fluctuates by more than 30% between spring and autumn.

Pulsed fluidic actuators play a central role in the fluid flow experimental control strategy to achieve better performances of aeronautic devices. In this paper, we demonstrate, through an experimental test bench, how the interpolatory-based Loewner Data-Driven Control (L-DDC) framework is an appropriate tool for accurately controlling the outflow velocity of this family of actuators. L-DDC combines the concept of ideal controller with the Loewner framework in a single data-driven rationale, appropriate to experimental users. The contributions of the paper are, first, to emphasise the simplicity and versatility of such a data-driven rationale in a constrained experimental setup, and second, to solve some practical fluid engineers concerns by detailing the complete workflow and key ingredients for successfully implementing a pulsed fluidic actuator controller from the data acquisition to the control implementation and validation stages., Comment: 20 pages, 7 figures

International audience; Intraband absorption in doped nanocrystals offers an interesting alternative to narrow band gap materials to explore mid infrared optoelectronic device designs. However, the performance of such device clearly lags behind the ones relying on intrinsic materials. Livache et al. have proposed a dye sensitized approach to overcome the limitations observed from intraband materials (high dark current, slow response, low activation energy), where the intraband absorber is coupled to an undoped material which takes care of the charge conduction. Here, we unveil the coupling between both materials using mid-infrared transient reflectivity (TR) measurement. We show that hybrid material displays a unique feature in the TR signal that we attribute to a charge transfer and for which the dynamic matches the hopping time. We then developed a strategy to enhance the photodetection performances of the hybrid material by coupling for the first time intraband absorption to a light resonator. The latter is used to enhance the absorption by a factor 4 and enables an increase of the operating temperature by 80 K compared to the reference device. The obtained device matches the performance of best devices relying on intraband absorption.

International audience; This letter proposes a novel robust interval observer for a two-dimensional (treated as a synonym for a double-indexed system) linear time-invariant discrete-time system described by the Fornasini-Marchesini second model. This system is subject to unknown but bounded state disturbances and measurement noise. Built on recent interval estimation strategies designed for one-dimensional systems, the proposed observer is based on the introduction of weighting matrices which provide additional degrees of freedom in comparison with the classical structure relying on a change of coordinates. Linear matrix inequality conditions for the exponential stability and peak-to-peak performance of a two-dimensional system described by the Fornasini-Marchesini second model are then proposed, and applied to the design of a robust interval observer. Numerical simulation results are provided to show the efficiency of the proposed estimation strategy.

International audience; This paper deals with a new definition of the Radar Cross Section (RCS) suitable for surface wave propagation in the HF band. Indeed, it can be shown that the classical definition of the RCS is dependent on distance for this kind of propagation. Also, in simulation, with the classical definition, the power estimated on the receivers using the radar equation is inaccurate. This is an issue for the performance assessment of High Frequency Surface Wave Radars. Thanks to the analysis of different wave propagation models, the differences between the space wave propagation and surface wave propagation have been highlighted. The required modifications of the RCS can then be performed. The proposed new definition is explained and justified in the paper and has been successfully applied to the computation of the RCS of naval targets. In addition, the implementation of this normalization term into the radar equation, and conversely the gain, is discussed. It can be observed that the received power, determined with the definitions adjusted to the surface wave propagation, is accurate. The different obtained results are illustrated and commented.

International audience; Numerous glacier velocity observations, derived from spaceborne imagery, are available online, but it remains difficult to analyze them because they are measured with different temporal baselines, by various sensors. In this study, we propose a novel formulation of the temporal closure to fuse multi-temporal multi-sensor velocity observations without prior information on the displacement behavior and the data uncertainty. We establish a system of linear equations between combinations of displacement observations and fractions of estimated displacements. The proposed approach provides a velocity time-series with a regular and optimal temporal sampling, the latter representing a compromise between the temporal resolution and the signal-tonoise ratio. The proposed approach is first evaluated on synthetic datasets and second on Sentinel-2 and Venµs velocity observations over the Fox glacier in New Zealand. The results show the intraannual variability of Fox glacier surface velocity with a reduced uncertainty and complete temporal coverage.

International audience; This paper presents the development of an ontology for opinion mining in French corpora. Since ontology construction from scratch is expensive and time consuming, the model is built by adapting an existing ontology modeling appraisal categories in English. The construction method consists of two main steps: first, the ontology of appraisals is translated in French by using a conceptto-concept approach; then different adaptation strategies are implemented to improve the result of this translation. Adaptation strategies are based on text mining, weakly supervised methods and the use of WordNet to refine the model. The goal of the adaptation phase is to cope with limitations of concept-to-concept translation, to integrate concepts and relations from external corpora and resources, and to build a model that captures various features of opinions. The ontology was designed and build to incorporate linguistic and extra linguistic information on the description of opinions in French. The model was validated by using both expert insights to validate the relevance of concepts and relations and formal criteria to describe the ontology qualities for practical use.

International audience; This article presents a data-based methodology to build Reynolds-Averaged Navier-Stokes (RANS) wall models for aerodynamic simulations at low Mach numbers. Like classical approaches, the model is based on nondimensional local quantities derived from the wall friction velocity u τ , the wall viscosity µ w , and the wall density ρ w. A fully-connected neural network approximates the relation u + = f (y + , p +). We consider reference data (obtained with RANS simulations based on fine meshes up to the wall) of attached turbulent flows at various Reynolds numbers over different geometries of bumps, covering a range of wall pressure gradients. After training the neural networks on a subset of the reference data, the paper assesses their ability to accurately recover data for unseen conditions on meshes that have been trimmed from the wall up to an interface height where the learned wall law is applied. The network's interpolation and extrapolation capabilities are quantified and carefully examined. Overall, when tested within its interpolation and extrapolation capabilities, the neural network model shows good robustness and accuracy. The global error on the skin friction coefficient is a few percent and behaves consistently over all the considered test cases.

Characterizing the boundary layer transition to turbulence around realistic hypersonic vehicles is a challenging task due to the numerous parameters that affect the process. To address this challenge, the cone-cylinder-flare (CCF) geometry has been designed to provide a flow topology that captures various transition mechanisms observed on reentry objects, such as absolute and convective instabilities, which are dependent on the free stream conditions. In this study, a global linear stability analysis is performed on the CCF model at Mach=6.0 to investigate and map the dominant instabilities at wind tunnel flow conditions. We examine optimal responses and forcings computed using resolvent analysis, as well as global modes originating from the recirculation bubble at the cylinder flare junction. The effects of bluntness are assessed through analyses of both blunt and sharp configurations. Our results shed light on the linear flow mechanisms that promote the transition to turbulence around such hypersonic objects., Comment: Conference paper

International audience; Large aperture periodically-poled Rb:KTP crystals designed for optical parametric amplifiers in 2 µm LIDAR systems were radiation hardness tested by exposure of proton beams at 10 MeV and 60 MeV energies. An irradiation dose of 55 Gy was used to commensurate the crystals' estimated exposure on board a mission in the low-Earth orbit. The irradiation effects were investigated by comparing optical transmission spectra and 2D effective nonlinearity mapping in a 2 µm OPO setup before and after irradiation. The results reveal that the periodically poled structure remained intact after irradiation, and the changes in the optical transmission and nonlinear properties were close to the measurement uncertainty. This investigation is essential for realizing efficient frequency converters for space applications, such as spaceborne active greenhouse gas monitoring LIDAR instruments or correlated photon-pair sources.

International audience; Context. Adaptive optics (AO) is a technique allowing for ground-based telescopes' angular resolution to be improved drastically. The wavefront sensor (WFS) is one of the key components of such systems, driving the fundamental performance limitations.Aims. In this paper, we focus on a specific class of WFS: the Fourier-filtering wavefront sensors (FFWFSs). This class is known for its extremely high sensitivity. However, a clear and comprehensive noise propagation model for any kind of FFWFS is lacking. Methods. Considering read-out noise and photon noise, we derived a simple and comprehensive model allowing us to understand how these noises propagate in the phase reconstruction in the linear framework.Results. This new noise propagation model works for any kind of FFWFS, and it allows one to revisit the fundamental sensitivity limit of these sensors. Furthermore, a new comparison between widely used FFWFSs is held. We focus on the two main FFWFS classes used: the Zernike WFS (ZWFS) and the pyramid WFS (PWFS), bringing new understanding of their behavior.; Contexte: L'optique adaptative (OA) est une technique permettant d'améliorer de façon drastique la résolution angulaire des télescopes terrestres. L'analyseur de surface d'onde (WFS pour WaveFront Sensing en anglais) est l'un des composants clés de ces systèmes, ce qui entraîne des limitations de performance fondamentales.Objectifs: Dans cet article, nous nous concentrons sur une classe spécifique de de WFS : les capteurs de front d'onde à filtrage de Fourier (FFWFS). Cette classe est connue pour sa sensibilité extrêmement élevée. Cependant, un modèle clair et complet de propagation du bruit pour tout type de FFWFS fait défaut.Méthodes: En considérant le bruit de lecture et le bruit photonique, nous dérivons un modèle simple et complet permettant de comprendre comment ces bruits se propagent dans la reconstruction de phase dans le cadre linéaire.Résultats: Ce nouveau modèle de propagation du bruit fonctionne pour tout type de FFWFS, et permet de revisiter la limite de sensibilité fondamentale de ces capteurs. De plus, une nouvelle comparaison entre les FFWFS les plus utilisés est effectuée. Nous nous concentrons sur les deux principales classes de FFWFS utilisées : le Zernike WFS (ZWFS) et le pyramid WFS (PWFS), apportant une nouvelle compréhension de leur comportement.

International audience; Visible nanocrystal-based light-emitting diodes (LEDs) are about to become commercially available. However, their infrared counterparts suffer from two key limitations. First, III–V semiconductor technologies are strong competitors. Second, their potential for operation beyond 1.7 µm remains unexplored. The range from 1.5 to 4 µm corresponds to a technological gap in which the efficiency of interband quantum-well-based devices vanishes and quantum cascade lasers are not efficient enough. Powerful infrared LEDs in this range are needed for applications such as active imaging, organic molecule sensing and airfield lighting. Here we report the design of a HgTe nanocrystal-based LED with luminescence between 2 and 2.3 µm. With an external quantum efficiency of 0.3% and radiance up to 3 W Sr−1 m−2, these HgTe LEDs already present a competitive performance for emission above 2 µm.

International audience; Optical parametric oscillators are versatile devices for generating a tunable coherent radiation from an incident laser beam. They rely on nonlinear frequency conversion to cover spectral ranges that are poorly or not covered by direct laser emission. This article presents a short overview of the optical parametric oscillators principles of operation, main implementations and related applications.

In this paper, we present the MESSII Dataset (Manipulator Experimental SyStem Identification and Interaction Dataset). This novel dataset aims at providing numerous sequences of movements of the KUKA iiwa manipulator, in order to evaluate methods for identification and estimation of the robot's dynamic parameters and signals, respectively. Different movements of the manipulator are provided, including trajectories moving one or multiple joints at the same time, trajectories that are specially designed for parameter identification, and trajectories including a payload attached at the end-effector of the manipulator. The information obtained from the propioceptive sensors of position and torque is presented. Furthermore, as physical Human-Robot Interaction (pHRI) is the main application of this robot, sequences with interaction with a person are provided to estimate the forces applied, where a force-torque sensor acts as the ground truth. The dataset can also be used in ROS to evaluate real-time methods as information is presented in rosbags files. Possible applications are given, highlighting the advantage of the dataset to help with state-of-the-art challenges, without the need of the real robot nor doing new and complex experiments. The dataset, as well as more information and tools, are publicly available in https://messii-dataset.enit.fr.

International audience; This work presents a study of the microstructure and mechanical properties of a TNM+ alloy (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, in at.%) densified by Spark Plasma Sintering (SPS), in comparison to the as-SPSed TNM alloy, which contains neither carbon nor silicon. Tensile tests at room temperature and 800 °C, as well as creep tests at 800 °C and 200 MPa, were performed. The microstructures and the fracture surfaces of deformed samples were studied by scanning and transmission electron microscopies, as well as by X-ray diffraction. The deformation mechanisms were investigated by means of in situ straining experiments and post-mortem analyses of deformed samples, both performed by transmission electron microscopy. Contrary to the TNM alloy, the as-SPSed microstructure of the TNM+ alloy does not contain β/βo phase due to the incorporation of carbon. At room temperature, the TNM+ alloy exhibits a yield stress of 520 MPa but a poor ductility of less than 0.1% of plastic strain. The incorporation of carbon and silicon leads to an increase in the creep resistance of the alloy at 800 °C. Despite the fact that iron inclusions are responsible for the premature failure of some samples during tensile tests, the TNM+ alloy is found to be able to deform plastically at room temperature by the glide of ordinary dislocations and by twinning.; Ce travail présente une étude de la microstructure et des propriétés mécaniques d'un alliage TNM+ (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, en at.%) densifié par Spark Plasma Sintering (SPS), en comparaison avec l'alliage TNM brut de SPS qui ne contient ni carbone ni silicium. Des essais de traction à température ambiante et 800°C ainsi que des essais de fluage à 800°C et 200 MPa ont été réalisés. Les microstructures et les surfaces de rupture des échantillons déformés ont été étudiées par microscopie électronique à balayage et à transmission, ainsi que par diffraction des rayons X. Les mécanismes de déformation ont été étudiés au moyen d'expériences de déformation in situ et d'analyses post-mortem d'échantillons déformés, toutes deux réalisées par microscopie électronique à transmission. Contrairement à l'alliage TNM, la microstructure brute de SPS de l'alliage TNM+ ne contient pas de phase bêta/bêta0 en raison de l'incorporation de carbone. Malgré le fait que les inclusions de fer soient responsables de la rupture prématurée de certains échantillons lors des essais de traction, l'alliage TNM+ est capable de se déformer plastiquement à température ambiante. L'incorporation de carbone et de silicium conduit à une augmentation de la résistance au fluage de l'alliage à 800°C.

International audience; The next generation of giant ground and space telescopes will have the light-collect-ing power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are opti-mized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ∕D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.; La prochaine génération de télescopes terrestres et spatiaux géants aura la capacité de collecter la lumière pour détecter et caractériser des exoplanètes terrestres potentiellement habitables en utilisant pour la première fois une imagerie à contraste élevée. Cela ne sera réalisable que si les performances des systèmes d'optique adaptative extrême (ExAO) des télescopes à miroir à segmentés géants (GSMT) sont optimisées à leur plein potentiel. Un composant clé d'un système ExAO est le senseur de front d'onde (WFS), qui mesure les aberrations de la turbulence atmosphérique. Un choix courant dans les instruments actuels et de prochaine génération est le senseur de front d'onde pyramidal (PWFS). Les systèmes ExAO nécessitent un échantillonnage spatial et temporel élevé des fronts d'onde pour optimiser les performances et en conséquence nécessitent des détecteurs de grande taille pour le WFS. Nous présentons une démonstration de banc d'essai en boucle fermée d'un capteur de front d'onde pyramidal à trois côtés (3PWFS) comme alternative au capteur conventionnel de front d'onde pyramidal à quatre côtés (4PWFS) pour les applications GSMT-ExAO sur l'optique adaptative complète innovante et l'instrument de test coronographe ( CACTUS). Le 3PWFS est moins sensible au bruit de lecture que le 4PWFS car il utilise moins de pixels détecteurs. Le 3PWFS a un avantages supplémentaire : une optique pyramidale à trois côtés de haute qualité est plus facile à fabriquer qu'une pyramide à quatre côtés. Nous décrivons la conception des deux composants du système CACTI, le simulateur d'optique adaptative et le banc d'essai PWFS qui comprend à la fois un 3PWFS et un 4PWFS. Nous détaillons le budget d'erreur du système CACTI, passons en revue ses procédures de fonctionnement et d'étalonnage, et discutons de son état actuel. Une expérience préliminaire a été réalisée sur CACTI pour étudier les performances de la 3PWFS à la 4PWFS dans différentes forces de turbulence en utilisant à la fois l'intensité brute et les méthodes de traitement du signal de la carte des pentes. Cette expérience a été répétée pour un rayon de modulation de 1,6 et 3,25 λ∕D. Nous avons constaté que les performances des deux capteurs de front d'onde sont comparables si les gains de boucle modale sont réglés.

International audience; One of the most promising solutions to access high power laser chains is to achieve a coherent combination of a large number of elementary lasers. To interfere constructively, these laser sources should be identical and operate under the same conditions. However, despite these efforts, differential delays appear in the course of time, which must be compensated for. While designing the required correction system, knowing the behavior of a laser as a function of the environmental conditions is not crucial, whereas having access to the differences in the behaviors of identical lasers is, leading to difficulties in modeling. The purpose of this paper is to illustrate how a large set of lasers can be simultaneously analyzed to estimate their variations and optimize a correction system. The X-Coherent Amplified Network laser relies on 61 fiber amplifiers, which are as identical as possible. This state of the art femtosecond digital laser therefore appears as an ideal candidate to study a large number of fiber lasers working under controlled conditions.; L'une des solutions les plus prometteuses pour accéder à des chaînes laser de haute puissance consiste à réaliser une combinaison cohérente d'un grand nombre de lasers élémentaires. Pour interférer de manière constructive, ces sources laser doivent être identiques et fonctionner dans les mêmes conditions. Cependant, malgré ces efforts, des retards différentiels apparaissent au cours du temps, qui doivent être compensés. Lors de la conception du système de correction requis, connaître le comportement d'un laser en fonction des conditions environnementales n'est pas crucial, alors qu'avoir accès aux différences de comportements de lasers identiques l'est, ce qui entraîne des difficultés de modélisation. Le but de cet article est d'illustrer comment un large ensemble de lasers peut être analysé simultanément pour estimer leurs variations et optimiser un système de correction. Le laser XCAN repose sur 61 amplificateurs à fibre, qui sont aussi identiques que possible. Ce laser "numérique" femtoseconde de pointe apparaît donc comme un candidat idéal pour étudier un grand nombre de lasers à fibre fonctionnant dans des conditions contrôlées.

International audience; With the approach of next generation supersonic transport entry into service, new research activities were initiated to support updates on ICAO regulations and certification processes for supersonic transport vehicles. Within this context, the EU Horizon 2020 SENECA project has been launched to investigate the levels of noise and gaseous emissions in the vicinity of airports as well as the global climate impact of next generation supersonic civil aircraft. This paper introduces some of the preliminary outcomes of this investigation. It presents the preliminary design and performance analysis of a Mach 1.6 business jet, following an integrated aircraft-engine design approach. The preliminary design was performed accounting for the limitations posed by future environmental restrictions on respective subsonic vehicles. The market space and mission route definition exercise assumed only "over-sea" supersonic operations, while for "over-land", only subsonic operations where allowed. Parametric studies on engine integrated design demonstrated modest core temperatures while cruising and the significant impact of engine installation on performance. At this first design iteration, assuming current state of the art technology, the Mach 1.6 business jet showed good potential to satisfy the predicted mission requirements while respecting the environmental constraints in terms of Landing & Take-Off (LTO) noise and emissions.; Avec la mise en service prochaine d’avions de transport supersoniques de nouvelle génération, de nouvelles activités de recherches ont été démarrées pour aider à la mise à jour des procédures de régulation et de certification de l’OACI pour les avions de transport supersoniques. Dans ce contexte, le projet européen Horizon 2020 SENECA a été lancé pour étudier les niveaux ce bruit et les émissions de polluants à proximité des aéroports, ainsi que l’impact global sur le climat des avions supersoniques civils de nouvelle génération. Ce papier illustre certains résultats préliminaires de cette étude. Il présente la conception préliminaire et l’analyse de performances d’un avion d’affaire supersonique à Mach 1.6, selon une approche intégrée de conception avion-moteur. La conception préliminaire a été réalisée en prenant en compte les limitations posées par les futures restrictions environnementales sur les aéronefs subsoniques. L’exercice de définition de l’espace de marché et de la mission considère le vol supersonique uniquement au-dessus des océans, tandis que le vol reste subsonique au-dessus des terres. Des études paramétriques sur des concepts avec moteur ont démontré une température interne modeste pendant le vol de croisière et l’impact significatif de l’installation du moteur sur les performances. Pour cette première itération, en considérant l’état de l’art actuel des technologies, l’avion d’affaire à Mach 1.6 montre un bon potentiel pour satisfaire les exigences attendues de la mission tout en respectant les contraintes environnementales en terme de bruit au décollage et à l’atterrissage (bruit LTO) et les émissions.

International audience; The EU-funded project ALTERNATE aims to explore the possibility of broader use of sustainable aviation fuels (SAFs). Part of the project assesses the effect of SAFs on soot production using experimental results and model predictions. In this regard, the combustion of two fuels was investigated under high-pressure conditions on the MICADO test rig at ONERA. This combustor allows a detailed analysis of soot formation based on advanced laser diagnostics. During the experimental campaign, the effect of Jet A-1 and Alcohol to Jet (ATJ) on soot levels was studied for three operating conditions in which the pressure of the combustion chamber varied from 4.5 to 9 bar, while maintaining almost constant the fuel-to-air ratio. An investigation of spray formation, flame shape and combustion dynamics is carried out to shed light on the impact of fuel composition on soot formation. In addition, the sooting behavior of the two fuels is compared, and it is observed that ATJ has a lower sooting capacity than Jet A-1 for the studied conditions. In parallel, Safran Tech and CERFACS worked jointly to perform Large Eddy Simulation (LES) for the case 4.5 bar fueled with Jet A-1. Semi-detailed chemistry for fuel oxidation and gaseous soot precursors together with the Lagrangian Soot Tracking model, both developed by CERFACS, is applied, and a first comparison against the available experimental data in terms of spray evolution and flame shape is obtained. The present work gives an overview of the experimental data collected during ALTERNATE, of SAF effects on soot generation and a first comparison obtained with LES for the Jet A-1 case at 4.5 bar.

International audience; The extent to which the introduction of subwavelength spatial modulation of electromagnetic properties improves absorption performances is studied. The proposed absorber represents an evolution from the Salisbury screen, whereby the uniform resistive layer is replaced by a metagrating. A periodic supercell that supports only the specular reflection is first designed, and load impedances are then engineered to suppress this diffraction mode. To experimentally demonstrate the concept, four prototypes are fabricated and tested in the microwave domain around 10 GHz. Furthermore, the performances assessed by a merit factor derived from Rozanov’s bound show that the use of metagratings opens up good perspectives for improving the state of the art. Our findings can pave the way toward the development of high performance absorbers for applications across a broad frequency spectrum.

International audience; Different additive manufacturing (AM) technologies such as L-PBF and DED do become really attractive for both repair and 3D part manufacturing. In particular, extensive work is in progress for the non-weldable nickel-based superalloys which tend to exhibit cracks due to residual stresses build-up during AM thermal cycles. Within the framework of the project FAPS conducted at Université Paris-Saclay, the present investigation will highlight the processing conditions and build-up strategy that produce crack-free specimens for alloy AD730®. The latter was developed by Aubert & Duval for cast&wrought gas turbine applications. In this work, a comparison between such conventional processing and AM will be provided in terms of mechanical performance. The results clearly show an anisotropic behaviour related to the sharp crystallographic texture induced by the epitaxial grain growth. The results will be discussed, with a perspective analysis of maturity for this AM processedmaterial, the process robustness, the potential technological developments and application prospects.; Différentes technologies FA telles que L-PBF et DED deviennent réellement attractives pour à la fois de la réparation et de la fabrication de pièces 3D. En particulier, un travail important est en cours pour les superalliages base Ni non soudables qui tendent à se fissurer en raison d’une augmentation des contraintes résiduelles lors des cycles thermiques FA. Dans le cadre du projet FAPS mené à Paris-Saclay, ces travaux vont mettre en exergue les conditions de process et de stratégie de construction qui produisent des échantillons sans fissures pour l’alliage AD730. Ce dernier a été développé par Aubert&Duval pour des applications coulé+forgé dans les turbines aéronautiques. Dans ce travail, on présentera une comparaison entre un tel procédé conventionnel et la FA en termes de performance mécanique. Les résultats montrent clairement un comportement anisotrope relié à la forte texture cristallographique induite par la croissance épitaxiale des grains. On discutera des résultats, avec en perspective l’analyse de la maturité de ce matériau issu de FA, la robustesse du procédé, les développements technologiques potentiels et les applications prospectives.

International audience; While the integration of nanocrystals as an active medium for optoelectronic devices progresses, light management strategies become required. Over recent years, several photonic structures (plasmons, cavities, mirrors, etc.) have been coupled to nanocrystal films to shape the absorption spectrum, tune the directionality, and so on. Here, we explore a photonic equivalent of the acoustic Helmholtz resonator and propose a design that can easily be fabricated. This geometry combines a strong electromagnetic field magnification and a narrow channel width compatible with efficient charge conduction in spite of hopping conduction. At 80 K, the device reaches a responsivity above 1 A•W-1 and detectivity above 10 11 Jones (3 µm cutoff) while offering a significantly faster time-response than vertical geometry diodes.

International audience; Space lidar instruments for missions like AEOLUS or MERLIN require advanced high-power laser systems with according technical and financial effort. In order to increase the impact of such missions, it is advantageous to expand the versatility of their instruments. In the case of trace gas sensing, the ability to detect multiple trace gas species with the same instrument greatly enhances their value. Multi-species trace gas differential absorption lidar (DIAL) systems require absolute frequency referencing across large spectral bandwidths. While absorption cell based references need individual lasers at online and offline wavelengths for each species, a broadband mode locked laseroffering a frequency combcan provide the required frequency accuracy over the complete spectral range of the lidar instrument. In the frame of the LEMON project, we developed a combined design for an absolute frequency reference based on a wavemeter for coarse frequency determination (

International audience; The MICROSCOPE satellite ended its mission in October 2018. Aiming at testing the Equivalence Principle (EP), the funding hypothesis of the General Relativity with unprecedented precision, a first publication in 2017 showed no evidence of a violation at 10−14 level. Since then; 3 years of analysis made it possible to improve the accuracy by one order of magnitude, placing this test as a reference for the test of General Relativity (GR). This presentation will focus on the most challenging topic of the data analysis: estimating errors and ensuring the best accurate test. The final result will be discussed and its impact on alternative theories to GR will be given.

The space mission MICROSCOPE dedicated to the test of the Equivalence Principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations ($a_{\rm A}$ and $a_{\rm B}$) of two test masses in terms of the E\"otv\"os parameter $\eta({\rm{A, B}}) = 2 \frac{a_{\rm A}- a_{\rm B}}{a_{\rm A}+ a_{\rm B}}$. No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 hours down to the limit of the statistical error which is smaller than $10^{-14}$ for $ \eta({\rm{Ti, Pt}})$. Accumulating data from all segments leads to $\eta({\rm{Ti, Pt}}) =[-1.5\pm{}2.3{\rm (stat)}\pm{}1.5{\rm (syst)}] \times{}10^{-15}$ showing no EP violation at the level of $2.7\times{}10^{-15}$ if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the E\"ot-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null E\"otv\"os parameter with a statistical uncertainty of $1.1\times{}10^{-15}$., Comment: Class. Quantum Grav. 39 204009

International audience; In the context of lightning strike impacting aeronautical fasteners, we investigate the in situ behaviour of fasteners subject to a current level of a few kA by using high-speed Xray phase-contrast imaging in a synchrotron facility. It reveals that the fastener erosion occurs in two time scales. On a microsecond timescale, hot particles are ejected from cavity walls of the Carbon fibre reinforced polymer due to sparking/arcing phenomena, whereas on a sub-millisecond time scale, the fastener wall is vaporized due to the electrical energy deposited in the arc-fastener interface. The experimental observations have been used as input for an electro-thermal model of electric contact. The estimated vaporised depth is in good agreement with the measured one. The nature of the internal damages has been confirmed by using X-ray phase tomography.

National audience; L'apprentissage de distance propose d'optimiser la distance de Mahalanobis pour des problèmes de classification. Plusieurs algorithmes associés à ce problème s'interprètent comme des estimateurs d'une matrice de covariance. Partant de ce constat, nous proposons un nouveau problème d'estimation appelé Robust Geometric Metric Learning (RGML) qui vise à estimer une matrice de covariance par classe et leur barycentre riemannien. Deux algorithmes associés à ce problème d'estimation sont développés : RGML gaussien et RGML Tyler. Ces algorithmes optimisent deux fonctions de coût sur la variété riemannienne des matrices symétriques définies positives et sa sous-variété à déterminant unitaire. Enfin, les algorithmes proposés sont appliqués sur des jeux de données réels. De bonnes performances ainsi qu'une robustesse aux données mal étiquetées sont obtenues.

National audience; Cet article a pour but de présenter un nouvel algorithme pour améliorer l'estimation des phases SAR interférométriques (InSAR) dans le contexte de séries temporelles. Basée sur l'estimateur du maximum de vraisemblance d'un modèle gaussien multivarié, l'estimation des phases InSAR est résolue en utilisant une approche de Descente en Bloc de Coordonnées (DBC). Par rapport aux approches classiques, l'amélioration principale réside dans l'estimation conjointe de la cohérence interférométrique et des phases InSAR au lieu de l'utilisation d'un estimateur annexe de cohérence, obtenue

International audience; Chalcogenide glasses are increasingly being developed for photonic applications, particularly in the field of mid-infrared optical imaging. In this paper, we study the photosensitivity of one chalcogenide to direct femtosecond laser writing and its possible applications to micro-optics. Particular attention has been paid to the creation of phase changes and related refractive index variations. This chalcogenide glass was compared with two commercial heavy oxide glasses: Schott SF10 and Corning 9754. We observed different types of permanent modifications depending on the writing speed and the laser pulse energy. Index variations were measured at Δn>+0.055 in the chalcogenide glass while maintaining spectral transmission similar to the pristine materials before irradiation. This provides a good candidate to design optical components for infrared application and helps to unlock the potential of the femtosecond laser direct writing technique to implement at high writing speed and high index changes with low optical losses

International audience; The impact damage tolerance remains for laminated composite materials one of the critical step in the design of aeronautical structures. Due to couplings between the different involved damage mechanisms (transverse cracks, delamination, fibre failure), the determination of the damage scenarios is still very challenging considering only post-mortem controls, such as C-Scan or more recently CT-Scan. Therefore, the present study is dedicated to the real time measurement of the evolution of different damage mechanisms during low velocity / low energy impact tests using high-speed infrared thermography. Impact tests at different energy levels were conducted on a T700GC/M21 quasi-isotropic laminate in order to demonstrate for different damage scenarios of increasing complexity the contribution of this measurement technique and to extract valuable information in order to validate simulation. Various post-mortem observation techniques (SEM, C-scan and X-ray tomography) are used in this study to validate and/or determine the chronology of the various damage events identified with infrared thermography measurements. Finally the projected damaged areas have been estimated with IR-thermography at the end of impact tests, based on methodologies available in the literature, and compared with other classical postmortem measurement methods. This comparison highlights that the assessment of the extent of damage by IR thermography tends to overestimate the extent of damage.