The French Aerospace Lab ONERA
Recent publications
Between March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) which caused these record-shattering temperature anomalies. Here in Part II, we continue our large, collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt which was recorded along coastal areas, but this was outweighed by widespread, high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Finally, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea-ice extent.
Between March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of -9.4° C on March 18 at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/mid-latitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heatwave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heatwave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about one hundred years, a closer recurrence of such an event is possible under future climate projections. In a subsequent manuscript, we describe the various impacts this extreme event had on the East Antarctic cryosphere.
This paper presents the design of a self‐scheduled fault‐tolerant controller for the lateral/directional motion of MuPAL‐ research aircraft using a polynomial‐scheduled structured H control. The controller is designed to be tolerant against loss‐of‐efficiency faults in the aileron and rudder, but based on industrial best practices it is scheduled with respect to an overall fault level instead of with respect to the individual faults. The performance and robustness of the resulting controller is verified first using frequency and time domain analysis, and subsequently it is validated in the Aircraft‐In‐the‐Loop configuration of MuPAL‐, where the real aircraft is operated in research Fly‐By‐Wire mode by the pilot on‐ground while coupled to an emulation computer that simulates the aircraft flying motion. The results show good behavior of the controlled aircraft across the defined fault scenarios.
A very interesting class of metamaterials is characterized by supersymmetry (SUSY). What makes SUSY very attractive for the design of new optical devices is the possibility to define different spatial refractive index distributions (superpartners) having the same scattering spectra (angularly and spectrally). In this study we explore the possibilities offered by the generation of superpartners of vacuum, being reflectionless and possessing unit transmission by definition. In particular, broken-SUSY is used to define a reflectionless active cavity capable of amplifying electromagnetic radiation in the visible. The approach is analytical through the use of the Darboux transform (a type of supersymmetric transformation) for the generation of the optical potential and the calculation of the field, while the transmission/reflection spectra evaluation is done with the Transfer Matrix method. Interestingly, we show that the Darboux transform allows to define 1D materials that are reflectionless for a continuum of frequencies. Moreover, the proposed device behaves as a dynamic optical filter amplifying radiation arriving at large angles while for other directions is almost completely transparent. Thus, simply by rotation different functionalities can be obtained. In addition, the active filter is reflectionless for all wavelengths and angles of incidence.
This paper analyzes the different definitions of a negator of a probability mass function (pmf) and a Basic Belief Assignment (BBA) available in the literature. To overcome their limitations we propose an involutory negator of BBA, and we present a new indirect information fusion method based on this negator which can simplify the conflict management problem. The direct and indirect information fusion strategies are analyzed for three interesting examples of fusion of two BBAs. We also propose two methods for using the whole available information (the original BBAs and their negators) for decision-making support. The first method is based on the combination of the direct and indirect fusion strategies, and the second method selects the most reasonable fusion strategy to apply (direct, or indirect) based on the maximum entropy principle.
In preparation for a future wind tunnel test of a rotor with twist-actuated blades (STAR II), numerical predictions of this test have been carried out by the contributing partners. In this paper, the simulated results of the vortex-induced stall operating condition, synonymous with a highly loaded flight condition, are presented. The current conclusion is that a noticeable spread of the results is given when searching for the maximum attainable thrust, depending on the onset of stall once perceived by the individual simulation methodology. Some general trends among the simulations could still be identified with respect to the actuation settings that reduce vibrations and the required power. Generally, most CFD-based results allowed to capture this physical phenomenon, but carefully tuned low-fidelity aerodynamic tools also managed to capture the same trends at a fraction of the computational cost.
The study provided a base of comparison of known computational techniques with different fidelity levels for performance and noise prediction of a single, fixed-pitch UAV rotor operating with varying flight parameters. The range of aerodynamic tools included blade element theory, potential flow methods (UPM, RAMSYS), lifting-line method (PUMA) and Navier–Stokes solver (FLOWer). Obtained loading distributions served as input for aeroacoustic codes delivering noise estimation for the blade passing frequency on a plane below the rotor. The resulting forces and noise levels showed satisfactory agreement with experimental data; however, differences in accuracy could be noticed depending on the computational method applied. The wake influence on the results was estimated based on vortex trajectories from simulations and those visible in background-oriented schlieren (BOS) pictures. The analysis of scattering effects showed that influence of ground and rotor platform on aeroacoustic results was observable even for low frequencies.
The exergy concept originates from the field of static thermodynamics and expresses the maximum theoretically recoverable mechanical work from a system while it evolves toward its dead thermodynamic state. It accounts for both mechanical and thermal mechanisms, and it allows to separate reversible and irreversible losses in the system’s transformations. The physical insight provided by this concept motivated the development of an exergy-based performance evaluation method in the field of aerodynamics. The resulting formulation has the advantage of being independent of the feasibility of a drag/thrust breakdown (ambiguous for highly integrated engine concepts) and includes thermal effects in the performance metrics. It, however, relies on an adapted definition of exergy, in particular involving a dead state in motion. This adapted definition is not trivial and raises theoretical concerns due to fundamental thermodynamic properties of exergy not being always satisfied. This paper aims at proposing a corrected version of this definition that ensures that the fundamental properties of exergy are respected. First, the exergy concept is presented alongside the concerns raised by its original adaptation, which, to the best of the authors’ knowledge, has been used in all exergy-based flowfield analyses in the field of applied aerodynamics. Then, an unsteady exergy balance is derived in the geocentric reference frame (in which there are no ambiguities in the definition of exergy) and then transformed to a reference frame in translation. The corrected adaptation of the exergy definition for aerodynamics applications is extracted from this transformation and the impact on the exergy balance is analyzed.
Fluoropolymers such as polytetrafluoroethylene (PTFE), fluorinated-ethylene-propylene (FEP), and ethylene tetrafluoroethylene (ETFE) have been tested in the dedicated experimental facility SIRENE (ONERA, Toulouse, France) to perform electric analysis by a technique named thermo-stimulated-induced current (TSC) method. An experimental approach is presented in this article: the objective is to bring into evidence trap distribution and characteristics in space-used polymers by the TSC method and to get a better understanding of the physical mechanisms steering charge transport through isothermal current measurements. The extraction of the physical parameters was carried out with two methods: the initial rise method and the curve-fitting method. The implementation of these parameters in physics models developed at ONERA allows the improvement of our understanding and prediction of charging behavior and radiation-induced conductivity evolution of these polymers under space conditions.
Spacecraft interacts with the charged particles of the space environment, leading to their electrostatic charging. This charging depends on the surface materials and their exposure to space. Thus, it is different for different parts of the spacecraft. This differential charging is particularly important on solar panels, which are composed of various polarized elements juxtaposed over small distances. This leads to strong electric fields ultimately leading to electrostatic discharges (ESDs), themselves being the onset of destructive secondary arcs. Hence, controlling the onset of ESDs is a key factor to prevent damages on spacecraft. Two ways are generally envisioned to act on the ESD onset: the geometry of the solar cells and the material electrostatic properties. In this article, the control of the ESD onset is tackled through the study of the effects of the cover glass secondary emission properties on the voltage threshold of solar cell ESDs. This study is conducted numerically with the spacecraft plasma interaction software (SPIS)-ESD software, as the natural variability of physical samples and the impossibility to have materials with controlled characteristics render the experimental study unpractical, if even feasible.
Electrostatic discharges (ESDs) are known to be responsible for satellites anomalies during radiation belts disturbances. Few analyses have been performed so far on nanosatellites however. Ground testing is the most convenient method to evaluate spacecraft charging and its related effects in terms of ESDs and electromagnetic coupling (EMC). This article presents an experimental instrumentation that is fully possible to adapt and embed on nanosatellite mockups.
The modeling of the spacecraft surface interactions with space environments is accessible to everyone through integrated tools such as NASCAP, SPIS, MUSCAT, COMOVA, Systema, and a few others. These software applications target the effects of exposure to the space environment through models of material behaviors. These models require the measurements of full property sets for every material used on spacecraft in order for the software to provide the user with an accurate prediction. However, the available databanks are quite sparse and are barely sufficient to provide estimates of the level of risk undergone by the spacecraft. This lack of accurate data is directly related to the specificity of such measurements, which require long and complex experimental campaigns and are only performed in a few dedicated facilities. The cost of the full characterization of a single material is thus very high. In addition, modelers improve continuously their models, which would require re-characterizing periodically the materials. In order to ease the characterization of space materials, ONERA developed the characteristics of material interactions with the space environment (ChaMISEn) data management system. It is composed: of the ChaMISEn open-source data model for the description of the models, experimental setups, measurement data, and extracted material properties; of the COMPEx extraction software that performs the material property extraction using the metadata of the experimental setup, of the measurements and of the model; of distributed databases; and of libraries that allow connecting both experimental facilities and end-user software to the data system. We will present the ChaMISEn system as well as its integration into ongoing activities performed at ONERA. The capabilities of the system will be illustrated through the presentation of use cases related to spacecraft charging modeling.
This article presents a study on cathodoluminescence (CL) of different space-used fluoropolymers, such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and ethylene tetrafluoroethylene (ETFE). This experimental technique allows highlighting radiative energy transitions under electron irradiation and degradation mechanisms under high radiation doses. Samples were irradiated with an electron beam (10 keV–1 $\mu$ A) under vacuum (10 $^{-6}$ mbar). A parametric study has been performed to analyze especially the effect of temperature and the injected radiation dose on the CL spectra of these different polymers. The CL spectrum for these three materials is composed of three elementary contributions at 2.2, 2.4, and 3.75 eV, each of them being associated with specific processes in relation to different chromophores present in the materials or generated by electronic irradiation. A decline in the amplitude of the CL spectra with the increasing temperature or accumulated radiation dose has been observed on these fluoropolymers.
Combustion applications such as internal combustion engines are a major source of power generation. Renewable alternative fuels like hydrogen and ammonia promise the potential of combustion in future power applications. Most power applications encounter flame wall interaction (FWI) during which high heat losses occur. Investigating heat loss during FWI has the potential to identify parameters that could lead to decreasing heat losses and possibly increasing the efficiency of combustion applications. In this work, a study of FWI (CH4-air mixture) in a constant volume chamber, with a head-on quenching configuration, at high pressure in both laminar and turbulent conditions is presented. High-speed surface temperature measurement using thin junction thermocouples coupled with high-speed flow field characterization using particle image velocimetry (PIV) are used simultaneously to investigate the effect of pressure during FWI (Pint) and turbulence intensity (q) on the heat flux peak (QP). In laminar combustion regimes, it is found that QP is proportional to Pint0.35. The increase in q is shown to affect both Pint and QP. Finally, comparing QP versus Pint for both laminar and turbulent combustion regimes, it is found that an increase in q leads to an increase in QP (b = 0.76).
We recently found the formation of periodically arrayed rows of very fine Fe2Hf Laves phase by interphase precipitation on a eutectoid type reaction path: δ-Fe → γ-Fe+Laves in 9Cr ferritic alloys with a small addition of Hf. In the present work, the precipitate morphology and precipitation mode of Laves phase were investigated on the eutectoid path in Hf or Ta doped high Cr ferritic alloys. The precipitation mode was found to change from fibrous precipitation to interphase precipitation with raising the δ→ γ transformation kinetics. The transition would be related to the time availability for solute diffusion to grow the fibrous precipitates through the advancing interface boundary diffusion. The nucleation of interphase precipitation of Fe2Hf phase was measured to be ~2 orders of magnitude faster than that of Fe2Ta. A thermodynamical consideration suggests that the faster kinetics of the Fe2Hf phase mainly derived from the higher chemical driving force for the nucleation. Fullsize Image
This article presents the numerical computations performed at ONERA for the Seventh AIAA Drag Prediction Workshop. By introducing Reynolds numbers up to 30 million closer to the flight conditions, greater lift levels beyond the design point, and time-accurate simulations, this new session has allowed the previous studies to be extended. The Common Research Model aircraft configuration has been considered in its academic wing-body version and calculated in this work with point-matched structured grids. The ONERA Cassiopee software as well as the elsA solver and the FFDπ far-field drag code have been used. The grid convergence study has shown larger pressure drag variations than what was obtained at the cruise lift coefficient, but increasing the Reynolds number seems to reduce this trend. Then, the angle-of-attack sweep study with the lift, drag, and moment polars has given the opportunity to assess different numerical settings such as the Spalart–Allmaras and kω shear stress transport turbulence models with the quadratic constitutive relation approach (QCR-2000) and to discuss the comparison between computational fluid dynamics results and wind-tunnel data. Concerning the Reynolds number increase, it has appeared that the main part of drag reduction comes from the friction (∼60%) and viscous pressure drag (∼30%) components. The prediction of pitching moment increments due to Reynolds number variations still needs to be significantly improved. Finally, for an angle of attack above 4.00 deg, by the use of unsteady Reynolds-averaged Navier–Stokes computations, an unsteady buffet phenomenon has been observed and analyzed.
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1,085 members
Xavier Vancassel
  • CPVA - Scientific Foresight
Hubert Cantalloube
  • DEMR - Department of Electromagnetism and Radar
Xavier Briottet
  • DOTA - Department of Theoretical and Applied Optics
Ismael K. Ortega
  • DEFA - Department of Fundamental and Applied Energetics
Palaiseau, France