21549 research outputs found
Sort by
On the impact of fuel injection angle in Euler–Lagrange large eddy simulations of swirling spray flames exhibiting thermoacoustic instabilities
Get PDFThis study deals with the fundamental problem of combustion dynamics in gas turbine combustors op- erating with liquid fuel. In this framework the present work proposes the study of an academic liquid fueled combustor sensitive to thermoacoustic instabilities, simulated via high-fidelity Large Eddy Sim- ulations. The experimental setup addressed is SICCA-spray from EM2C laboratory featuring both stable and unstable flames depending on the combustion chamber length. The proposed analysis, based on the Euler-Lagrange modeling approach, studies the impact of the spray injection angle θ on both the stable flame and the triggering of the longitudinal combustor acoustic mode when using a longer quartz tube. For the liquid injection modeling, the FIM-UR semi-empirical model is adopted with three different θ values: θ = 35◦, 45° and 60°. In stable conditions, the spray angle is proven to have a negligible impact on the flame anchoring point, however, the mean flame length and fuel distribution are found to be slightly modified by the velocity at which droplets enter the combustion chamber. For the thermoacous- tically unstable conditions, two well-established stable limit cycles with the same frequency and similar amplitudes are obtained when fuel is injected at θ = 45◦ and 60°. Contrarily, the system stabilizes when θ = 35◦ pointing to the importance of the dynamics of the liquid film layer formed inside the injector for this setup. Likewise, this liquid film layer dynamics and its modeling appear critical as already suggested by previous studies on the same configuration. The detailed analysis of the thermoacoustically unstable different predictions is then performed through the investigation of the spatial fields of the local Rayleigh index obtained following the novel extension in the frequency domain of the Rayleigh criterion comple- mented by the application of Dynamic Mode Decomposition. It confirms that the injection angle of the liquid spray has a significant effect on the thermoacoustic response of the system. Indeed the influence of θ on the dynamics of the liquid fuel when entering the combustion chamber is proven to have an impact on the synchronization mechanism governing the liquid phase with respect to acoustics sustaining the observed limit cycles. More specifically, couplings at the liquid phase level are evidenced by introducing two novel indices correlating the fluctuations of liquid fuel volume fraction and evaporation rate with pressure
An MDO-based methodology for static aeroelastic scaling of wings under non-similar flow
Get PDFThe classical aeroelastic scaling theory used to design scaled models is based on the assumption that complete flow similarity exists between the full aircraft and the scaled model. When this condition is satis- fied, the scaling problem of the model can be treated as a structural design problem only, where the scaled aerodynamic shape is preserved. If, on the other hand, this hypothesis no longer holds—if the scaled model is constrained to fly at low speed and low altitude, for example—and both the aerodynamic shape and the flexibility of the structure are exactly scaled, then the static response exhibits significant discrepancies in the aerodynamic loads and structural displacement. To de- sign a flying demonstrator with scaled static response when flow similarity cannot be fulfilled, we present a multidisciplinary optimization based method that al- lows some freedom in the design of the wing shape (while keeping the scaled wingspan) to update the wing geometry and structural properties to ensure equivalent scaled loads and overall wing displacement. To illustrate this method, we apply it to a 1:5 version of the uCRM wing at subsonic flight condition. While the errors in air loads using the classical theory are around 16%, the presented method achieves errors lower than 1%, with a good agreement for the wingtip displacement
The SuperCam Instrument Suite on the NASA Mars 2020 Rover: Body Unit and Combined System Tests
Get PDFThe SuperCam instrument suite provides the Mars 2020 rover, Perseverance, witha number of versatile remote-sensing techniques that can be used at long distance as wellas within the robotic-arm workspace. These include laser-induced breakdown spectroscopy(LIBS), remote time-resolved Raman and luminescence spectroscopies, and visible and in-frared (VISIR; separately referred to as VIS and IR) reflectance spectroscopy. A remotemicro-imager (RMI) provides high-resolution color context imaging, and a microphone canbe used as a stand-alone tool for environmental studies or to determine physical propertiesof rocks and soils from shock waves of laser-produced plasmas. SuperCam is built in threeparts: The mast unit (MU), consisting of the laser, telescope, RMI, IR spectrometer, andassociated electronics, is described in a companion paper. The on-board calibration targetsare described in another companion paper. Here we describe SuperCam’s body unit (BU)and testing of the integrated instrument.The BU, mounted inside the rover body, receives light from the MU via a 5.8 m opti-cal fiber. The light is split into three wavelength bands by a demultiplexer, and is routedvia fiber bundles to three optical spectrometers, two of which (UV and violet; 245–340 and 385–465 nm) are crossed Czerny-Turner reflection spectrometers, nearly identical to theircounterparts on ChemCam. The third is a high-efficiency transmission spectrometer containing an optical intensifier capable of gating exposures to 100 ns or longer, with variable delaytimes relative to the laser pulse. This spectrometer covers 535–853 nm (105–7070 cm−1Ra-man shift relative to the 532 nm green laser beam) with 12 cm−1full-width at half-maximumpeak resolution in the Raman fingerprint region. The BU electronics boards interface withthe rover and control the instrument, returning data to the rover. Thermal systems maintain awarm temperature during cruise to Mars to avoid contamination on the optics, and cool thedetectors during operations on Mar
Can Uncertainty Propagation Solve The Mysterious Case of Snoopy ?
Get PDFBoth the number of man-made objects in space and human ambitions have been growing for the last few decades. This trend causes multiple issues, such as an increasing collision probability, or the necessity to control the space system with high precision. Thus, the need to perform an accurate estimation of the position and velocity of a spacecraft.
This article aims at using Taylor Differential Algebra (TDA), an uncertainty propagation method, by implementing an ephemeris propagation tool designed to propagate long term trajectories. It will be used in the case study of Snoopy, the lost lunar module of mission Apollo 10, to explore new scenarios thanks to Monte-Carlo estimations, performed on the data gathered by this propagator
Stability of Zener order in martensite: an atomistic evidence
Get PDFMartensite is a supersaturated solid solution of carbon in body-centered iron wherein interstitial carbon atoms preferentially occupy a single octahedral sublattice. Despite a century of research, the mechanism of this long-range ordering is still a subject of debate. Recently, Zener’s theory of ordering was challenged both experimentally and theoretically. In an attempt to settle the controversy, we investigated by density functional theory the ground states of Fe-C configurations having various degrees of order. We conclude that the fully Zener-ordered configurations are always the most stable energetically, thus confirming Zener’s theory. Comparison with mean-field elasticity and Ising-type modelling supports the elastic origin of Zener ordering
Soft sensor design for estimation of thermal behavior of encapsulating materials in power electronic module
Get PDFWith the emergence of new semi-conductor technologies, an increasing number of high integrated power electronic
modules are designed. The increase of reliability of power modules induces the precise knowledge of the local temperature, even if it cannot be measured at any location. In this paper, the design of a soft sensor, more precisely a linear functional observer, is proposed. It enables the estimation of the temperature at any location using measurements provided from thermal sensors located at a number of precise points. The aim is to design a reduced size observer that could be implemented on a real-time embedded target such as Digital Signal Processor. Consequently, it is necessary to obtain a minimal order observer to limit the computation complexity
Correlation between degree of crystallinity and bluing of Zn1–Co Al2O4 (0≤x≤1) nanopowders prepared by soft chemistry route
Get PDFIn this article, we report a facile precursor pyrolysis by sol-gel method to prepare spinel-type Cobalt-substituted zinc aluminate nanoparticles (Zn1–xCoxAl2O4, 0 ≤ x ≤ 1). The relationship between the degree of crystallinity and the optical properties under the effect of the calcination temperature was investigated. The synthesised powders were characterized by means of X-ray diffraction (XRD), Thermogravimetry and Differential thermal analysis (TG–DTA), field emission scanning electron microscopy (FE-SEM), Brunauer–Emmett–Teller analysis (BET), UV–Vis absorption spectroscopy analysis and colorimetric analysis (CIELab). A single-phase Zn1–xCoxAl2O4 (0 ≤ x ≤ 1) spinel was formed at an annealing temperature of 700 °C. Structural refinement via the Rietveld method shows that an annealing temperature in excess of 700 °C leads to a decrease in the amorphous phase rate. At 800 °C, the enrichment in 50% of cobalt leads to blue powders with a degree of crystallinity of approximately 92% and a quasi-spherical morphology of nanometric size less than 100 nm
Near-Optimal Pulse Design for Pilot-Aided Timing Estimation in Faster-than-Nyquist Systems
Get PDFFaster-than-Nyquist (FTN) signaling is a promising strategy to achieve high spectral efficiency at fixed constellation size, notably over power-constrained channels. However, various traditional synchronization techniques cannot be reused in presence of FTN-induced intersymbol-interference. In this paper, we focus on timing synchronization in a pilot-aided scenario, where both data and pilots are transmitted at an FTN rate. We propose a density-dependent and near-optimal pulse design with respect to the Cramér-Rao lower bound (CRB), under bandwidth and energy constraints. We show the benefits of an FTN-specific pulse design compared to conventional root-raised cosine filters; we also discuss the performance/complexity trade-off of the proposed solutions. Our results may be of interest in high-throughput systems where timing accuracy is essential (e.g., satellite communications)
Benchmark of wrinkling formulae and methods for pre-sizing of aircraft lightweight sandwich structures
Get PDFSandwich structures are widely used in many industrial applications and especially in light aviation.
The local buckling phenomenon named “wrinkling” is one of the primary causes of compressive failure
of such structures. Its calculation is a difficult practical problem since this phenomenon cannot be
captured by the GFEM (Global Finite Element Model) classically used for aircraft structure sizing.
Therefore, pre‐sizing involves the use of a wrinkling model, which can be found in the literature. In
practice, such models are used with high safety factors by the industry. This paper proposes an
evaluation of analytical wrinkling formulas in an industrial setting. Realistic applications involve a
framework (3D stress state, orthotropy, skin asymmetry) far from the assumptions on which most of
the analytical formulations are based. The case study is a sandwich composite beam subjected to uniaxial
compressive load. Limitations and assumptions of the analytical wrinkling models studied are
quantified and a discussion on the relevance of using simple formulas for the design of sandwich
structured composites is developed
Contribution au développement de médicament de thérapie innovante à base d'ASCS pour la réparation des lésions osseuses de la face de l'homme : comparaison des ASCS isolées du corps adipeux de la bouche et du tissus adipeux sous-cutané
Get PDFLes lésions des os de la face sont des pathologies fréquentes en médecine humaine, aux conséquences fonctionnelles et esthétiques lourdes pour les patients. Les thérapies cellulaires à base de cellules stromales mésenchymateuses dérivées de tissus adipeux sous-cutané (SC-ASCs) ont montré leur efficacité pour supporter la reconstruction osseuse. Mais le corps adipeux de la bouche, serait aussi une source originale et prometteuse de cellules stromales mésenchymateuses (CAB-ASCs). Nous présenterons dans une première partie une étude bibliographique exposant les éléments essentiels de la biologie de l’os, des cellules stromales mésenchymateuses et de l’état actuel des thérapies cellulaires appliquées aux os de la face. Dans un deuxième temps, nous présenterons le travail expérimental réalisé, ayant pour objectif de comparer les propriétés de différenciation mésodermique in vitro des CAB-ASCs et SC-ASC isolées à partir de tissu adipeux de mêmes donneurs, et capacité à soutenir la reconstruction osseuse in vivo dans un modèle de lésion osseuse de taille critique de la calvaria chez la souris, conjointement ou non à un biomatériau composé d’hydroxyapatite et de béta-tricalcium phosphate