Analyse aérodynamique et acoustique d'une architecture boxwing dans le cadre du projet PARSIFAL

International audienceThe present paper summarizes the main results obtained from the CFD analysis of a reference boxwing configuration designed during the initial phase of the PARSIFAL project, with focus on the assessment of its aerodynamic performance in the transonic regime. For such purpose, high-fidelity RANS computations have been carried out and a detailed inspection of the different drag sources, induced, wave and viscous drag components, is presented. In addition, preliminary results from the acoustic analysis of such innovative aircraft configuration are also discussed, concerning the impact of the engine location

A mixed midelity conceptual design process for Boundary Layer Ingestion concepts

Boundary Layer Ingestion (BLI) is a promising concept that helps improving aircraft aeropropulsive performance. However, it remains difficult to bring together OAD (Overall Aircraft Design) process and high-fidelity tools due to the time of response of complex disciplinary tools. ONERA has thus developed a mixed fidelity approach inside its in-house OAD platform. The purpose is to mix conventional and robust OAD methods with high levels of fidelity from disciplinary tools such as CFD (Computational Fluid Dynamics), FEM (Finite Element Model) or CAA (Computational Aero Acoustics). This paper focuses on the integration of rapid CFD tools inside the OAD process, in order to assess BLI benefits. The resulting process is validated against reference and experimental cases when available, or high-fidelity RANS data elsewhere. The paper intends to present the tools and their validation process. These modules are applied to the common inlet concept, which aims at ingesting00% of the fuselage boundary layer. The results demonstrate the potential gain on the Power Saving Coefficient (up to 3% obtained with the L2 BLI module without resizing loop) but with non-negligible fan losses (up to 1.5%)

Evaluation stochastique et simulation des réseaux radio

La capacité d'un réseau ad hoc sans fil passe mal à l'échelle lorsque le nombre $N$ de noeuds du réseau augmente. Si chaque noeud choisit un interlocuteur parmi les autres noeuds, le débit avec lequel les noeuds peuvent communiquer doit tendre vers $0$ au moins en $\mathcal{O}\left(1/\sqrt{N}\right)$ lorsque $N$ tend vers l'infini. Le problème fondamental des réseaux ad hoc sans fil est de trouver un compromis entre connectivité et parallélisme: il est nécessaire d'utiliser une puissance d'émission suffisante pour éviter d'avoir des noeuds isolés mais il faut aussi limiter cette puissance pour limiter les interférences et ainisi obtenir du parallélisme dans l'accès au médium. L'objectif principal de cette étude est de proposer des protocoles de routage qui permettent d'atteindre la borne asymptotique pour la capacité et de dépasser le résultat déjà connu de $\mathcal{O}\left(1/\sqrt{N\ln(N)}\right)$ dans le cadre des réseaux aléatoires sur le carré unité $[0,1]\times[0,1]$ avec un trafic également aléatoire. Une première approche à l'aide d'un routage local utilisant une puissance d'émission variable permet de se rapprocher de cette borne sans toutefois l'atteindre en raison d'une mauvaise répartition du trafic due à l'aspect aléatoire du réseau. Une seconde approche fondée sur la théorie de la percolation aboutit à l'existence avec une forte probabilité d'un nombre suffisant de chemins disjoints formés de {\og petits sauts \fg} et traversant le réseau. Ces chemins permettent d'acheminer l'ensemble du trafic avec suffisamment de parallélisme pour atteindre asymptotiquement un débit en $\Theta\left(\frac{1}{\sqrt{N}}\right)$ pour chaque noeud. On s'appuie en outre sur des simulations afin de valider empiriquement les résultats de l'analyse théorique

Aeroelastic Adjoint-Based Optimisation of Highly Flexible Aircraft Wing Configuration

This paper investigates benefits resulting from the use of coupled aeroelastic analysis for aerodynamic shape optimisation of a highly flexible wing. The study is carried out on the eXternal Research Forum model (XRF-1) specified by Airbus Commercial Aircraft, representative of a long-range aircraft configuration. Improvements delivered by considering aeroelastic effects for the evaluation of both the aerodynamic performance and the associated gradients are assessed with respect to the results obtained by freezing the wing flexibility in both primal and adjoint computations. An analysis of the impact on the different drag components is also illustrated based on the far-field drag breakdown. Results show that for induced drag, engaging flexibility only at the primal level still allows to capture first-order gain on the final performance. However, engaging coupled-adjoint sensitivities is key to completely master wave drag reduction on the considered highly flexible wing. Performance improvement obtained by increasing the number of design parameters is also investigated

Nickel isotope fractionation during metal-silicate differentiation of planetesimals: Experimental petrology and ab initio calculations

Metal-silicate fractionation of nickel isotopes has been experimentally quantified at 1623 K, with oxygen fugacities varying from 10−8.2 to 10−9.9 atm and for run durations from 0.5 to 1 h. Both kinetic and equilibrium fractionations have been studied. A wire loop set-up was used in which the metal reservoir is a pure nickel wire holding a silicate melt droplet of anorthite-diopside eutectic composition. During the course of the experiment, diffusion of nickel from the wire to the silicate occurred. The timescale to reach chemical equilibrium was fO2 dependent and decreased from 17 to 1 hour, as conditions became more reducing. The isotopic composition of each reservoir was determined by Multicollector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICPMS) after Ni purification. The isotopic composition was found to be constant in the metallic wire, which therefore behaved as an infinite reservoir. On the contrary, strong kinetic fractionation was observed in the silicate melt (δNi down to −0.98‰.amu−1 relative to the standard). Isotopic equilibrium was typically reached after 24 hours. For equilibrated samples at 1623 K, no metal-silicate fractionation was observed within uncertainty (2SD), with ΔNiMetal-Silicate = 0.02 ± 0.04‰.amu−1. Theoretical calculations of metal-silicate isotope fractionation at equilibrium were also performed on different metal-silicate systems. These calculations confirm (1) the absence of fractionation at high temperature and (2) a weak temperature dependence for Ni isotopic fractionation for the metal-olivine and metal-pyroxene pairs with the metal being slightly lighter isotopically. Our experimental data were finally compared with natural samples. Some mesosiderites (stony-iron meteorites) show a ΔNiMetal-Silicate close to experimental values at equilibrium, whereas others exhibit positive metal-silicate fractionation that could reflect kinetic processes. Conversely, pallasites display a strong negative metal-silicate fractionation. This most likely results from kinetic processes with Ni diffusion from the silicate to the metal phase due to a change of Ni partition coefficient during cooling. In this respect we note that in these pallasites, iron isotopes show metal-silicate fractionation that is opposite direction to Ni, supporting the idea of kinetic isotope fractionation, associated with Fe-Ni interdiffusion

A comparison betweenab initio calculated and measured Raman spectrum of triclinic albite (NaAlSi3O8)

Albite is one of the most common minerals in the Earth\u2019s crust, and its polymorphs can be found in rocks with different cooling histories. The characteristic spectrum of vibration of the albite mineral reflects its structural Si/Al ordering. In this study, we report on the comparison between the Raman spectrameasured on a natural and fully ordered (as deduced on the basis of single-crystal X-ray diffraction data) \u2018low albite\u2019, NaAlSi3O8, and those calculated at the hybrid Hartree\u2013Fock/density functional theory level by employing the WC1LYP Hamiltonian, which has proven to give excellent agreement between calculated and experimentally measured vibrational wavenumbers in silicate minerals. All the 39 expected Ag modes are identified in the Raman spectra, and their wavenumbers and intensities, in different scattering configurations, correspond well to the calculated ones. The average absolute discrepancy |\u394v| is ~3.4cm-1, being the maximum discrepancy |\u394v|max ~ 10.3 cm-1. The very good quality of the WC1LYP results allows for reliable assignments of the Raman features to specific patterns of atomic vibrational motion

Reduced partition function ratios of iron and oxygen in goethite

First-principles calculations based on the density functional theory (DFT) with or without the addition of a Hubbard U correction, are performed on goethite in order to determine the iron and oxygen reduced partition function ratios (β-factors). The calculated iron phonon density of states (pDOS), force constant and β-factor are compared with reevaluated experimental β-factors obtained from Nuclear Resonant Inelastic X-ray Scattering (NRIXS) measurements. The reappraisal of old experimental data is motivated by the erroneous previous interpretation of the low- and high-energy ends of the NRIXS spectrum of goethite and jarosite samples (Dauphas et al., 2012). Here the NRIXS data are analyzed using the SciPhon software that corrects for non-constant baseline. New NRIXS measurements also demonstrate the reproducibility of the results. Unlike for hematite and pyrite, a significant discrepancy remains between DFT, NRIXS and the existing Mössbauer-derived data. Calculations suggest a slight overestimation of the NRIXS signal possibly related to the baseline definition. The intrinsic features of the samples studied by NRIXS and Mössbauer spectroscopy may also contribute to the discrepancy (e.g., internal structural and/or chemical defects, microstructure, surface contribution). As for oxygen, DFT results indicate that goethite and hematite have similar β-factors, which suggests almost no fractionation between the two minerals at equilibrium