Papers by Guillaume Dufour
Journal of Physics D: Applied Physics, 2020
We report on a detailed numerical study of the two-phase operation of a surface Alternating Curre... more We report on a detailed numerical study of the two-phase operation of a surface Alternating Current (AC) Dielectric Barrier Discharge (DBD) actuator. We showcase that when the quasi-periodic regime has been established, residual volume and surface charges play an important role on the discharge evolution strongly coupling the positive and negative phases. It is shown that the quasi-neutral streamer discharge found on the positive phase serves as both a positive and negative charge generator and acts as a virtual anode. As the streamer is not attached to the dielectric surface, most of the surface charging occurs during its after-burn (relaxation) phase. The positive surface charge leads to an distant zone of high electric field and thus ion drift but also interacts majorly with the negative discharge phase. During the latter, microdischarges form near the active electrode and an intense cathode layer feeds with charges the discharge volume. Each microdischarge is followed by a plasma layer formation attached to the dielectric layer expanding further at each repetition until it occupies a volume linked to the streamer elongation length and positively charged surface portion. The strong coupling between the positive and negative phases along with the strong impact of the streamer discharge on both suggest implications that have been ignored so far in terms of EHD force production and its spatiotemporal distribution.
The 10th issue of Aerospace Lab is devoted to plasmas for aeronautics. The use of plasmas for aer... more The 10th issue of Aerospace Lab is devoted to plasmas for aeronautics. The use of plasmas for aerodynamics and combustion has gained growing interest in the past 20 years, and a whole scientific community is now dedicated to this field of research. The content of this special issue reflects the diversity of the applications and of the physical conditions where plasmas are applied: from the subsonic to the supersonic regime, from combustion chambers to external aerodynamics, and from thermal plasmas to cold plasmas. Both experimental and modeling aspects are covered, as the complexity of the physics involved render the joint approach necessary. This issue will give the reader an overview of the current activities in this new field of research, and a glimpse of the numerous studies and applications of plasmas that are to come in aeronautics.
2021 International Conference on Computer Communications and Networks (ICCCN), 2021
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Copyright
Journal of Physics D: Applied Physics, 2021
We show that the spatio-temporal electrohydrodynamic (EHD) force production in surface alternativ... more We show that the spatio-temporal electrohydrodynamic (EHD) force production in surface alternative current-dielectric barrier discharge (AC-DBD) actuators is strongly influenced by both the streamer regime during the positive phase and the micro-discharge regime during the negative phase. Focusing on the spatial EHD force profiles, we demonstrate that the ionic wind spatial distribution can only be explained by the positive contribution of the streamer regime. The location of maximum ionic wind is found to be directly linked with the maximum elongation of the streamers at several millimeters from the exposed electrode. In both positive and negative phases of the AC-DBD operation, residual volumetric and surface charges once again linked to the streamer formation and afterburn, result to a variety of positive EHD force zones which, when time-averaged in one AC period, contribute to the generation of the experimentally observed induced thin wall jet. Through a thorough elaboration of ...
45th AIAA Plasmadynamics and Lasers Conference, 2014
IEEE Transactions on Plasma Science, 2012
Material properties: secondary emission (under electron/proton/UV), conductivities (surface/vol... more Material properties: secondary emission (under electron/proton/UV), conductivities (surface/volume, intrinsic/RIC), field effect, sputtering (recession rate, products generation and transport) Equivalent circuit: coatings (RLC) + user-defined discrete components (RCV), implicit solver Sources: Maxwellian Axisymmetric two axes C-Albuquerque-20-24 Sources: Maxwellian, Axisymmetric, two axes Specific features: Time integration: control at each level (population, plasma, simulation) Numerical times: integrate fast processes over a smaller duration (electrons/ions, plasma/SC…) 11th SCTC 4 Multiscale capabilities: cell = box / 100,000 Modularity: OO (Java), "plug-in" classes (Java introspection)
arXiv: Applied Physics, 2020
We show that the spatio-temporal ElectroHydroDynamic (EHD) force production in surface AC-Dielect... more We show that the spatio-temporal ElectroHydroDynamic (EHD) force production in surface AC-Dielectric Barrier Discharge (AC-DBD) actuators is dictated by both the streamer regime during the positive phase and the micro-discharge regime during the negative phase. We demonstrate that the ionic wind spatial distribution can only be explained by the positive contribution of the streamer regime. The negative sub-cycle contributes also to positive x-directed force production while a strong negative force region exists near the exposed electrode, linked to the micro-discharge and cathode sheath layer formation. The extension of the EHD force leads to a maximum of the ionic wind velocity profiles located in several millimeters from the exposed electrode.
Résumé La consommation énergétique des serveurs de calculs représente une partie non négligeable ... more Résumé La consommation énergétique des serveurs de calculs représente une partie non négligeable de la consommation électrique mondiale. Gérer ainsi de manière fine les jobs s’éxécutant sur les grilles permet d’améliorer sensiblement l’efficacité énergétique des centres de calculs, qui représentent une part importante de la consommation liée à l’informatique. Il est difficile de tester, d’évaluer et de comparer les techniques de gestion de jobs ainsi que leur impact énergétique. De plus, avec la généralisation de la possibilité de migration de ces tâches, de nouveaux leviers de réduction de consommation apparaissent. Il devient alors possible de réduire la consommation de manière proactive, en choisissant de manière pertinente les tâches à migrer, ainsi que leur lieu de destination. Dans cet article, nous allons présenter une nouvelle approche basée sur une modélisation fluide pour résoudre la problématique de l’évaluation rapide et efficace de gestion de jobs dans les grilles de ca...
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Numerical Modeling of Dielectric Barrier Discharge Based Plasma Actuators for Flow Control : the COPAIER/CEDRE Example G. Dufour, F. Rogier
Aerospace
Resilience to uncertainties must be ensured in air traffic management. Unexpected events can eith... more Resilience to uncertainties must be ensured in air traffic management. Unexpected events can either be disruptive, like thunderstorms or the famous volcano ash cloud resulting from the Eyjafjallajökull eruption in Iceland, or simply due to imprecise measurements or incomplete knowledge of the environment. While human operators are able to cope with such situations, it is generally not the case for automated decision support tools. Important examples originate from the numerous attempts made to design algorithms able to solve conflicts between aircraft occurring during flights. The STARGATE (STochastic AppRoach for naviGATion functions in uncertain Environment) project was initiated in order to study the feasibility of inherently robust automated planning algorithms that will not fail when submitted to random perturbations. A mandatory first step is the ability to simulate the usual stochastic phenomenons impairing the system: delays due to airport platforms or air traffic control (ATC) and uncertainties on the wind velocity. The work presented here will detail algorithms suitable for the simulation task.
Mathematical and Computational Applications
Planning conflict-free trajectories is a long-standing problem in Air Traffic Management. Navigat... more Planning conflict-free trajectories is a long-standing problem in Air Traffic Management. Navigation functions designed specifically to produce flyable trajectories have been previously considered, but lack the robustness to uncertain weather conditions needed for use in an operational context. These uncertainties can be taken into account be modifying the boundary of the domain on which the navigation function is computed. In the following work, we present a method for efficiently taking into account boundary variations, using the Hadamard variation.
Plasma synthetic jet (PSJ) actuators are mainly used in order to control high speed flows. The ob... more Plasma synthetic jet (PSJ) actuators are mainly used in order to control high speed flows. The objective of this work is to get a better understanding of the arc created inside the actuator and of its interaction with the surrounding fresh gas which allows to transfer the required thermal energy to produce the jets. After an experimental characterisation of the system, a 2D axisymmetric EMHD solver has been developed to simulate the activity of a non-confined arc similar to the one generated inside the actuator cavity. The energy transfers are quantified and an estimation of the useful amount of the electrical energy to heat the gas is given. Therefore, this work gives an explanation to the important losses that have been observed both experimentally and by simplified energy deposition simulations.
Comptes Rendus Mathematique, 2015
ABSTRACT In this Note, we first present a model for droplet secondary breakup, in liquid sprays. ... more ABSTRACT In this Note, we first present a model for droplet secondary breakup, in liquid sprays. This model is based on the kinetic theory formalism and uses experimental correlations found in the literature (L.-P. Hsiang, G.M. Faeth, Int. J. Multiphase Flow 19 (5) (1993) 721–735; R. Maxey, J. Riley, Phys. Fluids 26 (4) (1983) 883–889; M. Pilch, C.A. Erdman, Int. J. Multiphase Flow 13 (6) (1987) 741–757) to determine the fragmentation rate and its outcome. We then conduct a mathematical study of the resulting kinetic equation. We prove, under some physically reasonable assumptions, an existence and uniqueness theorem and characterize the long-time behaviour of the solution. To cite this article: G. Dufour et al., C. R. Acad. Sci. Paris, Ser. I 336 (2003).
Measurement-based approaches with extreme value worst-case estimations are beginning to be profic... more Measurement-based approaches with extreme value worst-case estimations are beginning to be proficiently considered for timing analyses. In this paper, we intend to make more formal extreme value theory applicability to safe worst-case execution time estimations. We outline complexities and challenges behind extreme value theory assumptions and parameter tuning. Including the knowledge requirements, we are able to conclude about safety of the probabilistic worst-case execution estimations from the extreme value theory, and execution time measurements.
Mathematical and Computer Modelling, 2009
ABSTRACT The purpose of this paper is to propose a new model based on an asymptotic analysis for ... more ABSTRACT The purpose of this paper is to propose a new model based on an asymptotic analysis for the modelling of steady wire-to-wire corona discharges. The concept consists in dividing the discharges into regions of two kinds: two thin ionization layers at the vicinity of the electrodes and a much larger ion-drift region. Introducing the length of the ionization layer ε and using an asymptotic analysis to define a truncated system, a simplified kinetic can be considered for each region which allows finding quasi-analytical solutions. The method is validated by comparison with a classical scheme and the results show good agreement with experiments. Finally, an example of parametric study of the discharge is presented. Indeed, the ability of the model to provide solutions at low computational cost allows quickly performing such a study and could be useful to experimenters in order to suggest new geometric settings or experimental setups.
Proceedings of the 21st International conference on Real-Time Networks and Systems - RTNS '13, 2013
ABSTRACT Network calculus is a theory designed to compute guaranteed bounds on delays and memory ... more ABSTRACT Network calculus is a theory designed to compute guaranteed bounds on delays and memory usage for networks. One of its strength is its mathematical framework to function representation and manipulation for network analysis. Up to now, the papers looking at the scheduling with networking consider left-continuous curves, while papers looking at packets with networking consider right-continuous curves. Some other are merging the two, without any consideration on that incompatibility due to a different definition of the functions. This theoretical paper focuses on the mathematical problem of function continuity and especially the continuity of cumulative curves, those applied by the network calculus to represent network dynamics. The right-continuity extension to the network calculus is formalized and compared with the classical left-continuity hypothesis evaluating its impact on some of the main results for network calculus.
20th AIAA Computational Fluid Dynamics Conference, 2011
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Papers by Guillaume Dufour