Search

The time-resolved electrohydrodynamic force produced by single dielectric barrier discharge (DBD) actuators used for airflow control is computed from electric wind velocity measurements. Two actuator designs are investigated: a plate-to-plate and a wire-to-plate surface DBD because each of them produces a different discharge current. Results show that: (1) the high voltage active electrode shape plays a key role in the plasma physics, (2) the body force is highly unsteady with fluctuations up to about ten times its time-averaged value, and (3) the typical plate-to-plate DBD produces a positive force during the positive half-cycle and a negative force during the negative half-cycle when both cycles result in a positive force with the wire-to-plate DBD.

Flow control consists of manipulating flows in an effective and robust manner to improve the global performances of transport systems or industrial processes. Plasma technologies, and particularly surface dielectric barrier discharge (DBD), can be a good candidate for such purpose. The present experimental study focuses on optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry. Positive and negative polarities are compared in terms of current behavior, deposited energy, fast-imaging of the plasma propagation, and resulting modifications of the surrounding medium by using shadowgraphy acquisitions. Positive and negative pulses of voltage produce streamers and corona type plasma, respectively. Both of them result in the production of a localized pressure wave propagating in the air with a speed maintained at 343 m/s (measurements at room temperature of 20 °C). This suggests that the produced pressure wave can be considered as a propagating sound wave. The intensity of the pressure wave is directly connected to the dissipated energy at the dielectric wall with a linear increase with the applied voltage amplitude and a strong dependence toward the rising time. At constant voltage amplitude, the pressure wave is reinforced by using a positive pulse. The present investigation also reveals that rising and decaying periods of a single pulse of voltage result in two distinct pressure waves. As a result, superposition or successive pressure wave can be produced by adjusting the width of the pulse.

Flow separation control by a non-thermal plasma actuator is considered for a NACA 0015 airfoil at a chord Reynolds number of 1.9 × 105. Static hysteresis in the lift coefficient is demonstrated for increasing and then decreasing sinusoidal voltage amplitude supplying a typical single dielectric barrier discharge actuator at the leading edge of the model. In addition to these open-loop experiments, unsteady surface pressure signals are examined for transient processes involving forced reattachment and natural separation. The results show that strong pressure oscillations in the relatively slow separation process, compared to reattachment, precede the ultimate massive flow separation. To enhance the contrast between the parts of the signal related to the attached flow and those related to the incipient separation, RMS estimate of filtered values of Cp is used to define a flow separation predictor that is implemented in feedback control. Two simple controllers are proposed, one based on a predefined threshol...

The aim of the present work is to investigate the capability of a Wire-to-Square Tube Electrostatic Precipitator (or WST-ESP) to collect submicron particles using a Dielectric Barrier Discharge (DBD). A parametric study is carried out to evaluate the effects of four control variables that might affect the collection efficiency of the WST-ESP: diameter of the corona wire electrode, width of the ground electrode and the area of the tube section. The experimental data show that the wire diameter has a negligible effect on the WST-ESP collection characteristics. However, better overall performances can be obtained by putting in parallel several WST-ESPs with reduced section. The extension of the ground electrode and its discretization increase the collection efficiency.

A new method to reject ground clutter using the Amplitude and Phase EStimation (APES) method is proposed. The theoretical approach is followed by the application of this method to the rejection of such an interference in the frame of a bistatic passive radar using digital video broadcasting - terrestrial (DVB-T) transmitters.

not Available.

To produce hybrids, one member of the parental line is genetically made male-sterile. This male-sterile trait is encoded by mitochondria so that it is maternally inherited. Consequently, the progeny of a male-sterile plant is fully sterile. Nevertheless, during the handling of cytoplasmic male-sterile seed stocks, some mixture with seeds of the maintainer lines can occur. Up to the present time, the only way to check the homogeneity of the cytoplasmic male-sterile seed stock was to grow the plants until flowering time. We have developed a method which can be used immediately after the harvest, allowing us to check samples from both sunflower and sugar beet. We used the mitochondrial plasmid, present only in the maintainer lines, as a probe for the total nucleic acids prepared from the cytoplasmic male-sterile seed stocks which might be contaminated. The signals compared to those of samples artificially contaminated allow us to measure as few as one male-fertile seed in 1000 seeds in a rapid and accurate manner.

The dielectric barrier discharge (DBD) is a nonmechanical device able to generate electrohydrodynamic forces close to a dielectric wall. The generated “electric wind” is actually used to control airflow over various bluff bodies. In this study, a DBD actuator is investigated for the control of a round turbulent air jet. The separation along the bevel of a small angle (12°) axisymmetric diffuser is studied using LDV measurements for a 20 m s− 1 airjet velocity. The results demonstrate that a DBD actuator is suitable to separate a turbulent airflow naturally attached. Under actuation, a jet deflection of 13° is observed and the coherent structures are energized. Quasi-steady and unsteady actuations are also compared for excitation frequencies up to 400 Hz and the analysis of the turbulent spectra demonstrates that a vortex shedding could be forced at the excitation frequency (up to 160 Hz). The investigation of different duty-cycle regimes allows us to define a threshold value inducing similar flow modifica...

Two contrasts for the problem of multichannel blind deconvolution have been given and theoretically studied by Comon [1996]. The maximization of these criteria allows us to solve the problem of multi-input/multi-output (MIMO) blind deconvolution. In this paper, we show that many other contrast functions may be considered. The two aforementioned criteria are proved to be included in the wide class of contrast functions, which is here defined through simple conditions.

We analyze the modifications of the flow around a NACA 0015 airfoil when the flow is periodically perturbed with an electrohydrodynamic (EHD) actuator. The device used consists of two bare electrodes flush mounted on the surface of the profile operated in a discharge regime characterized by the formation of a plasma sheet contouring the body. In this study, we analyze the influence of the frequency of a periodic actuation on the aerodynamic performance of the airfoil. The analysis is undertaken with measurements of the surface pressure distribution and of the flow fields with Particle Image Velocimetry technique. The experiments indicate that at moderate Reynolds numbers (150000 15°).

The separation problem of an instantaneous mixture of deterministic or random source signals is addressed. We show that the separation can be realized through the nonorthogonal joint diagonalization of spatial quadratic time-frequency matrices. One advantage of the proposed method is that it does not require any whitening stage, and thus, it is intended to work even with a class of correlated signals. We also propose a general automatic time-frequency point selection procedure for the determination of the above matrices to be joint diagonalized. An analytical example and computer simulations are provided in order to illustrate the effectiveness of the proposed approach and to compare it with classical ones.

The paper deals with blind source separation by contrast function maximization. A general class of separation criteria valid for both i.i.d. and non i.i.d. sources is exhibited; it is based on third or higher order cross-cumulants between the separator outputs and fixed signals, called references. We show that this approach is applicable not only in a semi-blind context, but also in a completely blind scenario. The most interesting feature concerning our criteria is their quadratic form. It follows a highly simplified optimization procedure which we describe. Simulation results illustrate the validity of our approach, and the appeal of this new class of contrast functions.

Theabilityofanelectrohydrodynamicactuatortomodifythecharacteristicsofa e owovera e atplateisanalyzed. Thedeviceconsidered usese ush-mounted electrodes and a dcpowersupply to createa plasma sheeton thesurface of the plate. We analyze the mechanism of formation of this plasma sheet, which has some similarities with the phenomenon of streamer formation. Experimental results are presented concerning e ow visualizations obtained at low e ow velocities (o 1 m/s) and velocity e elds obtained with a particle image velocimetry technique for higher e ow velocities (range 11.0-17.5 m/s). These results show that the discharge can induce an important acceleration of the e ow close to the surface. ORONAS are self-sustaining discharges characterized by a strong inhomogeneity of the electric e eld cone guration and electrodes having a low curvature radius. This cone guration cone nes the ionization process to regions close to the high-e eld electrodes. Thus, in this phenomenon, there are active electrodes, surrounded by ionization regions where free charges are created, a low-e eld drift region where charged particles drift and react, and low-e eld passive electrodes. Coronas can be unipolar or bipolar if oneorbothelectrodesareactiveelectrodes.Bipolarcoronascanlead to the formation of streamers, weakly conducting plasma e laments extending from one electrode and carrying their own ionization re- gion ahead of themselves. Positive streamers are cathode directed and negative streamers anode directed. The physics of corona discharge occurring in a gas close to an insulating surfacehasnotbeen as widely studied as coronaswithout anyextraneousbodiesinthevicinityofthedischarge. 1;2 Becausethe discharge involves the movement of ions as well as a large amount of neutral particles, this situation becomes of special interest in aerodynamics for e ow and instabilities control. The induced e uid motion is usually called electroconvection or sometimeselectricwind.Coulombianelectroconvectiontakesplace ifthecoulombianforcesactingonthee uidparticlesarepredominant in relation to the polarization ones. This is usually the case when the e uid medium is air. The way the electric forces act on e uid particles may be explained by considering that ions in their drift motion from one electrode to the other will exchange momentum with the neutral e uid particles and induce their movement. Because currents involved in the process are so lowthat magnetic effects can be disregarded the phenomenon is described by the set of equations used in electrohydrodynamics (EHD) problems.

DC corona discharges and dielectric barrier discharges (DBD) in air at atmospheric pressure are often used in chemistry due to their capacity to produce non-equilibrium chemical reactions. Under certain conditions, they can generate a flow called “ionic wind”. In this thesis, the effect of injecting a mist of water droplets into such plasmas is studied and applied for in situ volatile chemical species gathering. The objective is to study the motion of the aerosol induced by the discharge and its precipitation on the plate wall of a point-to-plate reactor, by means of a Particles Image Velocimetry (PIV) device at high frequency (20 kHz). First, the acceleration of air by the ionic wind phenomenon is described, this flow exhibiting properties that strongly depend on the electrical signal supplying the discharge (amplitude, frequency and waveform). Secondly, the impact of the water droplets mist on the discharge and the mist flow in the gap between electrodes are analyzed. We demonstrated that the particle movement was mainly due to ionic wind, but that the electrostatic precipitation phenomenon was not negligible, especially close to the plate and in the area far away from the jet axis. Lastly, the amount of water gathered in different discharge setups is evaluated. Applying the process to chemistry did not succeed because the discharge was unstable in a closed reactor due to the water film that takes place on the wall of the reactor.; Les décharges couronnes DC et les décharges à barrière diélectrique dans l’air à pression atmosphérique sont souvent utilisées en chimie car elles ont la capacité de produire des réactions chimiques hors-équilibre. Dans certaines conditions, elles peuvent générer un écoulement appelé « vent ionique ». Dans cette thèse, l’effet de l’injection d’un brouillard de gouttelettes d’eau micrométrique dans de tels plasmas est étudié, pour être appliqué à la récupération d’espèce chimique volatile in situ. L’objectif est donc d’étudier la mise en mouvement de l’aérosol par la décharge et sa précipitation sur la paroi d’un réacteur de type pointe-plan, à l’aide d’un dispositif de Vélocimétrie par Image de Particules (PIV) à haute fréquence (20 kHz). Dans un premier temps, la mise en mouvement de l’air par le phénomène de vent ionique est décrite, cet écoulement présentant des propriétés qui dépendent fortement du signal électrique alimentant la décharge (amplitude, fréquence, forme d’onde). Dans un second temps, l’effet du brouillard de gouttelettes d’eau sur la décharge ainsi que l’écoulement du brouillard dans l’espace inter-électrodes sont analysés. On a ainsi pu démontrer que le déplacement des particules était majoritairement dû au vent ionique, mais que le phénomène de précipitation électrostatique n’était pas négligeable, surtout à proximité de la plaque et dans les régions éloignées du centre du jet. Enfin, la quantité d’eau récupérée est évaluée pour différentes configurations de décharges électriques. L’application du procédé à la chimie n’a pu aboutir du fait de l’instabilité de la décharge dans un réacteur fermé à cause du film d’eau, non désiré, se formant sur les parois.

The framework of this research is bistatic radars using non-cooperative transmitters. The study focuses on digital video broadcasting transmitters. Considering such transmitters leads to higher capabilities of detection compared to other kind of radio communication illuminators. The processing of real data collected from a fixed receiver in the case of different kind of targets (helicopter and boat) leads to a specific method of clutter rejection and target detection. It also provides precious information on statistical properties of the environment and allows to adapt space-time processing to noise-like signals. The following points are presented in the case of a fixe receiver : - clutter rejection and target detection method in the case of noise-like signals - validation on real DVB-T signals - determination of statistical properties of clutter; in the case of a mobile receiver : - adaptation of existing space-time processing methods and comparison of their performances - adaptation and generalization to the case of multiple targets of the hybridization of both a method of reduced dimension and a non statistical one focusing on the range cell under test - development of a new method of iterative clutter rejection and target detection; Le cadre de ces recherches est celui des radars bistatiques. Leurs avantages sont nombreux. Citons notamment, dans le domaine opérationnel : * exploitation potentielle de cibles de faibles niveaux de signature radar en monostatique, * amélioration de la couverture basse et très base altitude, * accroissement de la complexité des techniques de furtivité face à un tel radar, * discrétion (faible probabilité d'interception et d'exploitation), dans le domaine de l'emploi : * disparition des contraintes d'emploi d'un système rayonnant (dommages dus aux rayonnements sur le personnel, les armées et munitions, rayonnements non essentiels et compatibilité électromagnétique), * inutilité d'une allocation de fréquences, Enfin, dans le domaine du développement et du maintien en condition opérationnelle, une focalisation des coûts sur la partie réceptrice. Les méthodes de traitement spatio-temporel présentées sont génériques et peuvent est appliquées à toutes les formes d'onde. Le cas des émetteurs non coopératifs de télévision numérique terrestre est plus particulièrement étudié. Les propriétés radar de ce type d'émetteurs conduisent en effet à des capacités de détection accrues comparativement à d'autres types d'émetteurs de radiodiffusion (télephonie mobile, radio FM, radio numérique). L'étude de données réelles obtenues à partir d'un récepteur fixe (cible aérienne et marine) a non seulement conduit à développer une méthode spécifique de réjection du fouillis de sol et de localisation de cibles mais a également: * fourni de précieux renseignements sur la nature des environnements pouvant être rencontrés, * nourri la réflexion sur la façon d'adapter les traitements spatio-temporels adaptatifs à la nature particulière des signaux. Les éléments suivants sont présentés : * dans le cas d'un récepteur fixe: * développement, pour des formes d'onde quelconques, et validation sur signaux réels de type Digital Video Broadcasting Terrestrial (DVB-T), d'une méthode de réjection de fouillis et de localisation de cibles mobiles, * étude des propriétés statistiques de fouillis de sol, * dans le cas d'un récepteur mobile: * adaptation de méthodes spatio-temporelles de réjection de fouillis et comparaison de leurs performances respectives, * adaptation et généralisation au cas des cibles multiples et des antennes lacunaires de l'association d'une méthode de réjection en dimension réduite, la méthode Joint Domain Localized (JDL) et d'une méthode non-statistique focalisée sur la seule case distance- Doppler sous test, la méthode Direct Data Domain (D3), * développement d'une nouvelle méthode de réjection itérative du fouillis à partir des méthodes d'estimation spectrale.

International audience; We propose a framework for blind multiple filter estimation from convolutive mixtures, exploiting the time-domain sparsity of the mixing filters and the disjointness of the sources in the time-frequency domain. The proposed framework includes two steps: (a) a clustering step, to determine the frequencies where each source is active alone; (b) a filter estimation step, to recover the filter associated to each source from the corresponding incomplete frequency information. We show how to solve the filter estimation step (b) using convex programming, and we explore numerically the factors that drive its performance. Step (a) remains challenging, and we discuss possible strategies that will be studied in future work.

International audience; We consider the local Gaussian modeling framework for under-determined convolutive audio source separation, where the spatial image of each source is modeled as a zero-mean Gaussian variable with full-rank time- and frequency- dependent covariance. We investigate two methods to improve the accuracy of parameter estimation, based on the use of local observed covariance and auditory-motivated time-frequency representation. We derive an iterative expectation-maximization (EM) algorithm with a suitable initialization scheme. Experimental results over stereo synthetic reverberant mixtures of speech show the effectiveness of the proposed methods.

International audience; In this paper we propose a new algorithm for the joint eigenvalue decomposition of a set of real non-defective matrices. Our approach resorts to a Jacobi-like procedure based on polar matrix decomposition. We introduce a new criterion in this context for the optimization of the hyperbolic matrices, giving birth to an original algorithm called JDTM. This algorithm is described in detail and a comparison study with reference algorithms is performed. Comparison results show that our approach provides quicker and more accurate results in all the considered situations.

International audience; We address the issue of source separation in a particular informed configuration where both the sources and the mixtures are assumed to be known during a so-called encoding stage. This knowledge enables the computation of a side information which ought to be small enough to be watermarked in the mixtures. At the decoding stage, the sources are no longer assumed to be known, only the mixtures and the side information are processed to perform source separation. The proposed method models the sources jointly using latent variables in a framework close to multichannel nonnegative matrix factorization and models the mixing process as linear filtering. Separation at the decoding stage is done using generalized Wiener filtering of the mixtures. An experimental setup shows that the method gives very satisfying results with mixtures composed of many sources. A study of its performance with respect to the number of latent variables is presented.

In this thesis, we study the problem of the blind separation of over-determined linear convolutive real or complex mixtures of deterministic or random, statistically independent or correlated, stationary, cyclo-stationary or non-stationary and real or complex sources. We have developed approaches that combine the new (non-unitary) joint (block) diagonalization to two novel detectors of particular points to build the matrices set to be joint (block) diagonalized. The main avantages of the proposed approaches are that they are more direct since they do not require a pre-whitening stage any more and that they can be used with correlated signals. Concerning the joint lock-diagonalization algorithms, we have proposed four joint block-diagonalization algoritms. The first algorithm is iterative and based on an algebraic optimization scheme. The three other ones are based on gradient approaches. The first one relies upon a gradient approach, but the matrix gradient is approximated, whereas the two other ones are based on an exact calculus (one is based on the gradient approach, the other is based on the relative gradient approach). The optimal step size versions of these three algorithms is provided to accelerate their convergence. It means that the step size is computed algebraically at each iteration as the rooting of a 3rd-degree polynomial. The main advantage of the proposed algorithms is that they are more general (the real, positive definite or hermitian assumptions about the matrices belonging to the considered set are no more necessary and the found joint block diagonalizer can be either a unitary or a non-unitary matrix). They can also be applied to solve the joint diagonalization problem., Dans cette thèse, nous étudions le problème de la séparation aveugle de mélanges linéaires convolutifs sur-déterminés réels ou complexes de sources. Les sources considérées sont réelles ou complexes, déterministes ou aléatoires et dans ce dernier cas statistiquement indépendantes ou corrélées, stationnaires, cyclostationnaires ou non-stationnaires. Nous développons des approches combinant de nouveaux algorithmes de (bloc) diagonalisation conjointe (non unitaires) à de nouveaux détecteurs de points (temps-fréquence ou autres...) particuliers permettant d'élaborer le ou les ensembles de matrices devant être (bloc) diagonalisées conjointement. Les principaux avantages de ces approches sont d'être plus directes en ce se sens qu'elles ne requièrent plus de blanchiment préalable des observations. Elles permettent en outre d'aborder le cas réputé difficile des signaux corrélés. En ce qui concerne les algorithmes de (bloc) diagonalisation conjointe, nous proposons quatre nouveaux algorithmes sans contrainte d'unitarité sur la matrice recherchée. Le premier algorithme est de type algébrique itératif. Il est basé sur l'optimisation d'un critère de type moindres carrés. Les trois autres approches utilisent un schéma d'optimisation de type gradient. Dans un premier temps le calcul du gradient matriciel de la fonction de coût étudiée est approché. Puis dans un second temps le calcul exact est mené et deux nouveaux algorithmes sont proposés : l'un à base de gradient, l'autre à base de gradient relatif. Nous étudions les versions à pas fixe de ces trois algorithmes, puis les versions à pas optimal afin d'accélérer la convergence des algorithmes (le pas est alors recalculé algébriquement à chaque itération en cherchant les racines d'un polynôme d'ordre trois). Un lien avec la diagonalisation conjointe non unitaire est également établi. Ces algorithmes de bloc-diagonalisation conjointe possèdent l'avantage d'être généraux : les matrices de l'ensemble considéré ne sont ni nécessairement réelles, ni à symétrie hermitienne, ni définies positives et le bloc-diagonaliseur conjoint peut être une matrice unitaire ou non-unitaire.

The plasma actuator consists in an electrical discharge established in air at atmospheric pressure between two electrodes flush mounted on the surface of a test profile. Under Coulombic forces, ions created by this non-thermal plasma drift and induce a fluid motion called “ionic wind”. Here, this electrical process is used to modify the detachment or the reattachment of an airflow.The present report is divided in two parts.The first part is dedicated to the development of the actuator in order to obtain a stable and homogeneous discharge. Two discharges are investigated: a corona discharge and a dielectric barrier discharge (DBD). For the corona discharge, a DC or AC high voltage is applied between two wires placed inside grooves. The means electric field is about 8 kV/cm and the mean current is 1.5 mA/m for a mean electrical power of 75 W/cm2. The DBD is obtained by applying an alternative high voltage (some kV with frequency of 100 up to some kHz) between two electrodes disposed of each side of the dielectric. Ionic wind measurements showed that for both discharge the velocity is about 3 m/s at 1 mm above the surface of the test profile.In a second part, the effect of the actuator is analysed for airflow control. A preliminary study at low velocity (< 2 m/s) demonstrated the ability of the actuator to reattach a naturally detached airflow and to control eddies created downstream by a pulse discharge. At upper velocities (´ 30 m/s), the actuator is used to control the detachment and reattachment in the case of a plane mixing layer and a turbulent jet. Results showed that the control modified the development properties of the downstream airflow as the thickness of the mixing layer or jet deflection in the case of a turbulent jet. More, these lasts experiments seems indicated that the actuator is more efficient to detach an airflow than reattached it when the actuator used is the DBD.; L'actionneur « plasma » consiste en une décharge électrique établie dans l'air à pression atmosphérique à la surface d'un isolant. L'apport de quantité de mouvement induit par ces plasmas froids de surface, dû à la migration des ions soumis à la force de Coulomb et appelé "vent ionique", est utilisé ici pour modifier l'état collé ou décollé d'un écoulement. Le travail réalisé est divisé en deux parties. L'objectif de la première partie est de développer l'actionneur afin d'obtenir une décharge stable et homogène à travers deux exemples : la décharge couronne et la décharge à barrière diélectrique (DBD). La décharge couronne est obtenue en appliquant une haute tension, AC ou DC, entre deux fils placés à l'intérieur de rainures dans l'isolant. Le champ électrique moyen est de 8 kV/cm, pour un courant moyen de 1,5 mA/m pour une puissance électrique moyenne de 75 W/cm2. La DBD est obtenue en appliquant une haute tension alternative (plusieurs kV avec une fréquence allant de 100 à quelque kHz) entre deux électrodes placées de part et d'autre de l'isolant. Les mesures de vent ionique ont montré pour ces deux décharges une vitesse de 3 m/s environ à 1 mm au-dessus de la paroi.Dans une seconde partie nous avons testé les performances de l'actionneur pour le contrôle d'écoulements. Des essais préliminaires à faible vitesse (< 2 m/s) ont montré la possibilité de recoller un écoulement et de contrôler les structures crées en aval à l'aide d'une décharge pulsée. A plus haute vitesse (´ 30 m/s), nous avons contrôlé l'état collé ou décollé d'un écoulement dans le cas d'une couche de mélange plane et d'un jet à section rectangulaire. Nous avons alors observés des modifications sur les propriétés du développement aval de l'écoulement, comme par exemple l'épaisseur de couche de mélange ou de vectorisation du jet. Par ailleurs, ces derniers travaux semblent indiquer que l'actionneur est plus efficace pour le décollement que le recollement et lorsque l'actionneur utilisé est la DBD.