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3D reconstruction of turbulent wind using lidar measurements
No full textInternational audience3D wind speed measurement in turbulent wind is particularly interesting for several applications such as weather and climate forecasting, planning and safety of aircraft during their flight, transport of aerosols and pollution, monitoring of weather conditions in case disasters, wind power generation, forest fires and volcanic plume movement. In particular, it is critical for the current development of low consumption aircraft with high aspect ratio wings to increase their lift. However, such wings are sensitive to loads induced by turbulences. That is why they require using adaptive wings that modify their shape according to the 3D wind turbulence measured ahead of the airplane (so called feed-forward gust load alleviation). To this end, we have developed a UV molecular wind lidar with QMZ interferometer (see D. T. Michel et al. session C.01.11) that measures the wind projected on the lidar axes. The lidar is addressed along different axes to obtain the projections of the wind speed along each of them and reconstruct the 3D wind by inverting the matrix of projections. If this method works for homogenous wind, in case of turbulence, each projection is measured at different spatial position, so for slightly different wind which leads to large errors in the reconstructed wind field. Therefore, it is important to develop a specific algorithm to optimize the wind reconstruction in turbulent wind field. We propose a Bayesian inversion method close to Kriging (Gaussian processes) to reconstruct the 3D wind from lidar measurements. It consists in estimating the wind speed at any point in space by incorporating a priori modeling of turbulence physics. This approach is part of the general trend towards incorporating physics into machine learning methods (physics-informed kernel learning). Taking into account lidar instrumental errors, we show, through realistic simulations, that the Von Karman-type turbulent wind is well estimated ahead of the aircraft. We are also developing a method for optimizing lidar axis angles. The aim is to find the optimum configuration of these axes in space, so as to minimize wind estimation errors on the aircraft axis. These errors are given by the Bayesian inversion algorithm. On the basis of simulations with turbulence of varying intensity, we show that with 4 lidar axes well positioned in space, these errors are minimal. The proposed wind reconstruction methodology can be used in a variety of contexts where we need to determine the 3D wind from lidar measurements
Development of a surrogate model to predict the convective-diffusive heat flux during composite material thermochemical degradation
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Lidar backscattering model for soot aerosols
No full textInternational audienceAerosol lidar remote sensing relies on the interpretation of backscattered light to retrieve particle properties of interest. This study presents a novel analytical backscattering model for soot or black carbon aerosols, based on the Rayleigh-Debye-Gans for Fractal Aggregates (RDG-FA) approximation. This model is used to derive simple expressions for common lidar-relevant parameters, including differential backscattering cross section, lidar ratio (LR), mass-backscattering coefficients (MBC), backscattering color ratio (CR), and Å ngström exponent (BAE). The behavior of these lidar parameters is investigated as a function of wavelength, size, and aging. Key findings include a general decrease in LR, along with a clear dependence of CR and BAE on aerosol size as black carbon aggregates grow, for both freshly emitted and aged soot. These findings have highlighted the ability to model the variations of these parameters throughout the life cycle of black carbon, capturing the evolution from chain-like freshly emitted particles to more spherical aged particles. Furthermore, this study demonstrates the potential of the RDG-FA backscatter model to calculate key lidar parameters and improve the retrieval of soot aerosol products
Simulations hybrides RANS/LES d'un profil hyper-sustenté utilisant une loi de paroi linéarisée dynamique sur grilles cartésiennes hiérarchiques
No full textInternational audienceThis paper investigates the performances of the recently published Dynamic Linearized Wall Model in the framework of hybrid RANS/LES methods (ZDES mode 2 (2020)) for aeroacoustic studies. This method was derived in order to ensure a proper control of the numerical error on the total shear stress near the wall and provide appropriate grid convergence trends in wall-modeled simulations. Several wall-modeled simulations of the LEISA2 high-lift airfoil configuration are performed on hierarchical Cartesian grids, with different numerical implementations of the wall model. The results are thoroughly compared to experimental and LES reference results and demonstrate the superiority of this new Dynamic Linearized Wall Model upon more standard wall model implementations.Cet article étudie les performances d'une loi de paroi dynamique linéarisée récemment publié dans le cadre des méthodes hybrides rans/les (zdes mode 2 (2020)) pour les études aéroacoustiques. cette méthode a été développée afin d'assurer un contrôle adéquat de l'erreur numérique sur la contrainte de cisaillement totale près de la paroi et de fournir des tendances de convergence en maillage appropriées dans les simulations avec loi de paroi. plusieurs simulations avec loi de paroi de la configuration d'aile hyper-sustentée leisa2 sont réalisées sur des grilles cartésiennes hiérarchiques, avec différentes implémentations numériques de la loi de paroi. les résultats sont minutieusement comparés aux résultats expérimentauxet aux résultats de référence et démontrent la supériorité de cette nouvelle loi de paroi dynamique linéarisée par rapport aux implémentations plus standard de la loi de paroi
A review on the characterization, the modeling and the simulation of conducted and radiated emissions of Power Printed Circuit Board (PPCB)
No full textInternational audienceFor complete Electromagnetic Compatibility (EMC) studies at PCB and chip levels, we have conceived some demonstrators to precisely characterize and model the more realistic electromagnetic behaviors of circuits at PCB level. We want to keep understandings on effects and contributions on electrical and physical parameters of the different parts of a circuit on PCB. This description is focused on power chips of different semiconductor technologies, that are the main sources of electromagnetic noises in the range of the GHz. This is due to the very high switching times of these components that are nowadays under the thousands of nanoseconds and then can produce high frequency (HF) resonances. Emissions in conducted mode in power PCB are now over the MHz, even with a very low frequency voltage command (kHz). Then, radiated mode is inherently activated, because of the length of the wires and the dimensions of the Power PCB. The nominal design and dimensions, the choice of test points and HF connectors of our PPCB demonstrator are defined for both direct conducted measurements in differential and common mode, and for “equivalent Far-field” radiation measurements in TEM cells. We propose to review EMC/ EMI characterizations available for conducted and radiated evaluations of the emissions at component and circuit level. Then we present the different approaches for constructing an equivalent electrical or numerical model of the PPCB including its environment: packaging, cables, connectors and especially the insertion of probes and antenna, all contributors of the final EMC responses. Some examples of these "EMC Virtual Experiment", on demonstrators and case studies, would show the audience that they can master this methodology for their own EMC understandings and investigations. We illustrate this tutorial by some real uses and applications of this "Virtual Model " in some new and actual scientific and industrial topics: Multiphysics and external temperature impacts, conducted models for aerospace/MEA, couplings in traction chain of trains
High-speed fs/ps-CARS thermometry for supersonic H2/air combustion studies
No full textInternational audienceWe present the results of a hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps-CARS) thermometry campaign performed in a H 2 /air research supersonic scramjet combustor. In situ vertical and horizontal temperature profiles were retrieved upstream and downstream the combustion zone. The repetition rate of the measurement was adjusted in order to optimize the signal-to-noise ratio of the CARS signal depending on the local turbulence of the flow. Near the flame front, single-shot measurements were demonstrated at kHz rate to catch the high-speed temperature fluctuations. In steady flow zones downstream of the combustion, up to 100 shots integration was performed in order to increase the precision of the measurement. This measurement campaign allowed to build a valuable experimental database for comparison with a 3D numerical unsteady computational fluid dynamic (CFD) simulation developed at ONERA. This work demonstrates the efficiency of hybrid fs/ps-CARS to perform single-shot kHz thermometry inside large-scale supersonic combustor
Diminution du bruit de volet Krueger sur une maquette de demi-avion
No full textInternational audienceDuring the aircraft approach and landing phase, airframe noise is a predominant concern, with leading edge high-lift devices being a major contributor. Traditionally, classical slats are employed for this purpose. However, an alternative solution is the Krueger leading edge flap, a prerequisite for laminar wing technology - a promising innovation to enhance aircraft efficiency and reduce emissions. This device was experimentally investigated in the Airbus-led German INTONE project. Specifically designed for a 3D wing, it was tested in DNW's low-speed wind tunnel acoustic test section in Braunschweig.The present study focuses on simulating flow and noise for two experimental configurations, aiming to validate these simulations against measurement data. Two high-lift designs are examined:1. A conventional slat, and2. A Krueger flap selected for its acoustic benefit.Unsteady flow simulations around the 3D wing model utilize the lattice-Boltzmann method. Acoustic time pressure signals are derived from both direct flow simulation noise and Ffowcs-Williams and Hawkings surface integration. Favorable comparisons are observed between simulated results and experimental data, including static pressure measurements on the wing model and far-field microphone recordings.Pendant la phase d'approche et d'atterrissage de l'avion, le bruit de cellule est une source de bruit dominante, les dispositifs hyper-sustentateurs y contribuant largement. Traditionnellement, des becs sont utilisés au bord d'attaque de l'aile pour augmenter la portance. Cependant, une solution alternative est le volet de bord d'attaque Krueger qui est un dispositif nécessaire à la technologie des ailes laminaires, ces dernières étant une innovation prometteuse pour améliorer l'efficacité de vol des avions et réduire leurs émissions. Le dispositif de volet Krueger a fait l'objet d'une étude expérimentale dans le cadre du projet allemand INTONE, dirigé par Airbus. Spécialement conçu pour une aile 3D, il a été testé dans la section d'essais acoustiques de la soufflerie à basse vitesse de DNW à Braunschweig.Notre étude se concentre sur la simulation de l'écoulement et du bruit pour deux configurations expérimentales, dans le but de valider ces simulations par rapport aux mesures aéroacoustiques. Les deux configurations expérimentales se distinguent par leur dispositif au bord d'attaque de l'aile:1. Une configuration avec un bec classique, et2. Une configuration avec un volet Krueger, sélectionné pour ses avantages acoustiques.Les simulations d'écoulement instationnaire autour du modèle d'aile 3D utilisent la méthode de Boltzmann sur réseau. Les signaux acoustiques de pression temporelle sont dérivés à la fois du bruit de la simulation directe de l'écoulement et de l'intégration des surfaces de Ffowcs-Williams et Hawkings. Des comparaisons favorables sont observées entre les résultats simulés et les données expérimentales, comprenant les mesures de pression statique sur le modèle d'aile et les enregistrements de microphone en champ lointain
Influence of Blade Bending and Torsion on Propeller Whirl Flutter
No full textInternational audienceThe whirl flutter aeroelastic instability is a major concern for propeller-driven aircraft. Classical models generally involve a propeller with rigid blades mounted on a flexible support. However, with modern engines trending toward slender and lighter blades, concerns arise about the influence of blade flexibility on this phenomenon. This study addresses this question by conducting an in-depth analysis of the impact of blade elasticity on whirl flutter stability. A structural model of a propeller is developed using beam theory, complemented by two other models to predict motion-induced aerodynamic loads. The first approach employs a quasi-steady assumption, while the second incorporates unsteady flow effects through a state-space formulation. These models are combined to evaluate the individual impact of blade deformation in out-of-plane bending, in-plane bending, and torsion on whirl flutter. The combined effect of all these deformations is then analyzed, revealing that blade flexibility has a significant stabilizing influence for conventional blade stiffness values. It also gives rise to unusual phenomena, such as forward whirl instabilities, which do not occur with rigid blade propellers. The main insight from this research is that blade elasticity can no longer be overlooked, as it plays a significant role in whirl flutter stability
Analyse des réponses diélectriques d’assemblages polymères complexes des ballons stratosphériques
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Dynamique vibrationnelle du fer pentacarbonyl en solution d'alcane revisitée
No full textInternational audienceWe explore the solvent-dependence of the vibrational dynamics of Fe(CO)5 (IPC) using a novel 2D-IR setup. A 320 pixel MCT camera allows us to achieve high spectral resolution within a large detection window, which can be matched in excitation by scanning coherence times of up to 250 ps. The dynamics of the IR active modes of IPC in the C–––O stretching range are probed in a series of alkanes of different chain lengths and viscosities. 2D-IR maps at short waiting times reveal the detailed anharmonic structure of the modes at play: we determined the cross-anharmonicity between the A′′2 and E′ modes (δ = −0.8±0.1 cm), and we are able to differentiate the diagonal anharmonicity of the doubly degenerate mode (ΔE ≃ 18 cm) from its non-diagonal anharmonicity (ΔE ≃ 11 cm). Our analysis of the polarization dependence of the 2D-IR signals strongly confirms an exchange mechanism between the IR-active modes due to Berry pseudo-rotation, which shows very little dependence on solvent viscosity, in contrast to the anisotropy loss. The implications of our findings for the exchange mechanism are discussed