Ces travaux portent sur la résolution successive de deux problèmes inverses en transferts thermiques : l'estimation de la densité de flux en surface d'un matériau puis de la conductivité thermique équivalente d'une couche déposée en surface de ce matériau. Le modèle direct est bidimensionnel orthotrope (géométrie réelle d'un matériau composite), instationnaire, non-linéaire et ses équations sont résolues par éléments finis. Les matériaux étudiés sont les composants face au plasma (tuiles composite carbone-carbone) dans le Tokamak JET. La densité de flux recherchée varie avec une dimension spatiale et avec le temps. La conductivité du dépôt de surface varie spatialement et peut également varier au cours du temps pendant l'expérience (toutes les autres propriétés thermophysiques dépendent de la température). Les deux problèmes inverses sont résolus à l'aide de l'algorithme des gradients conjugués associé à la méthode de l'état adjoint pour le calcul exact du gradient. La donnée expérimentale utilisée pour la résolution du premier problème inverse (estimation de flux surfacique) est le thermogramme fourni par un thermocouple enfoui. Le second problème inverse utilise, lui, les variations spatio-temporelles de la température de surface du dépôt inconnu (thermographie infrarouge) pour identifier sa conductivité. Des calculs de confiance associée aux grandeurs identifiées sont réalisés avec la démarche Monte Carlo. Les méthodes mises au point pendant ces travaux aident à comprendre la dynamique de l'interaction plasma-paroi ainsi que la cinétique de formation des dépôts de carbone sur les composants et aideront au design des composants des machines futures (WEST, ITER). / This work deals with the successive resolution of two inverse heat transfer problems: the estimation of surface heat flux on a material and equivalent thermal conductivity of a surface layer on that material. The direct formulation is bidimensional, orthotropic (real geometry of a composite material), unsteady, non-linear and solved by finite elements. The studied materials are plasma facing components (carbon-carbon composite tiles) from Tokamak JET. The searched heat flux density varies with time and one dimension in space. The surface layers conductivity varies spatially and can vary with time during the experiment (the other thermophysical properties are temperature dependent). The two inverse problems are solved by the conjugate gradient method with the adjoint state method for the exact gradient calculation. The experimental data used for the first inverse problem resolution (surface heat flux estimation) is the thermogram provided by an embedded thermocouple. The second inverse problem uses the space and time variations of the surface temperature of the unknown surface layer (infrared thermography) for the conductivity identification. The confidence calculations associated to the estimated values are done by the Monte Carlo approach. The method developed during this thesis helps to the understanding of the plasma-wall interaction dynamic, as well as the kinetic of the surface carbon layer formation on the plasma facing components, and will be helpful to the design of the components of the future machines (WEST, ITER).

Le nettoyage des surfaces métalliques est nécessaire dans différents domaines de l'industrie moderne. L'industrie nucléaire cherche de nouvelles méthodes de décontamination des surfaces oxydées, et les installations thermonucléaires nécessitent le nettoyage des composants face au plasma pour enlever la couche déposée contenant tritium. L'ablation laser est proposée comme une méthode efficace et sûre pour le nettoyage des surfaces métalliques et leur décontamination. Le facteur important influençant le chauffage et l'ablation laser est la distribution en profondeur de l’intensité laser. Le modèle de propagation de la lumière dans une couche diffusant sur un substrat métallique est développé et appliqué pour analyser les caractéristiques de distribution de lumière. Pour simuler les surfaces contaminées, l'inox AISI 304L a été oxydé par laser et chauffé dans un four. La contamination radioactive de la couche d'oxyde a été simulée par l'introduction d’europium et / ou de sodium. Un facteur de décontamination de plus de 300 a été démontré avec le régime de nettoyage optimal trouvé. Une diminution de la résistance à la corrosion a aussi été montrée après un nettoyage laser. Les seuils d'ablation des surfaces ITER-like (représentatives d’ITER) ont été mesurés. Une vitesse de nettoyage de 0,07 m2/W∙h a été trouvée. Pour les surfaces miroir, les seuils de dommages étaient déterminés pour éviter les dommages lors du nettoyage au laser. La possibilité de restaurer la réflectivité après le dépôt d’une couche mince de carbone a été démontrée. Les perspectives de développement ultérieur de nettoyage laser sont discutées. / Metal surface cleaning is highly required in different fields of modern industry. Nuclear industry seeks for new methods for oxidized surface decontamination, and thermonuclear installations require the cleaning of plasma facing components from tritium-containing deposited layer. The laser ablation is proposed as an effective and safe method for metal surface cleaning and decontamination. The important factor influencing the laser heating and ablation is the in-depth distribution of laser radiation. The model of light propagation in a scattering layer on a metal substrate is developed and applied to analyse the features of light distribution. To simulate the contaminated surfaces, the stainless steel AISI 304L was oxidized by laser and in a furnace. Radioactive contamination of the oxide layer was simulated by introducing europium and/or sodium. The decontamination factor of more than 300 was demonstrated with found optimal cleaning regime. The decreasing of the corrosion resistance was found after laser cleaning. The ablation thresholds of ITER-like surfaces were measured. The cleaning productivity of 0.07 m2/hour∙W was found. For mirror surfaces, the damage thresholds were determined to avoid damage during laser cleaning. The possibility to restore reflectivity after thin carbon layer deposition was demonstrated. The perspectives of further development of laser cleaning are discussed.

科学研究費補助金 研究種目:一般研究(A) 課題番号:01420044 研究代表者:高村 秀一 研究期間:1989-1991年度

Ces travaux de recherche ont pour but d’évaluer la méthode dite de la "Simulation auxEchelles Adaptées" (SAS pour Scale-Adaptive Simulation). Cette approche coïncide avec uneapproche RANS classique dans les zones pariétales attachées et adapte le niveau de viscositéturbulente dans les zones décollées pour y permettre une résolution partielle des structures turbulentes.Dans une première partie, une analyse théorique du modèle SAS original a été menéeet a permis de développer une correction visant à favoriser l’adaptation du niveau de viscositéturbulente dans les zones sièges d’instabilités de type Kelvin-Helmholtz. Le modèle ainsi corrigéest nommé SAS-αL. Les modèles SAS et SAS-αL ont été implantés dans le code de calculNavier-Stokes elsA de l’ONERA. À l’issue de cette étape, trois cas académiques d’écoulementsturbulents instationnaires, cylindre à grand nombre de Reynolds, marche descendante et cavitétranssonique, ont été simulés grâce aux trois modèles de turbulence SST, SAS et SAS-αL. Outreune comparaison aux bases de données expérimentales disponibles, une attention particulièrea été portée à l’influence de paramètres numériques tels que des schémas numériques d’ordreélevé. Enfin, afin d’étudier la viabilité de l’approche SAS dans un contexte industriel, les troismodèles de turbulence ont été testés sur une configuration issue de l’industrie aéronautique etcorrespondant à la sortie d’air chaud d’un système de dégivrage des nacelles d’avion. La comparaisondes prévisions obtenues avec les modèles SST, SAS et SAS-αL aux données expérimentalesobtenues à l’ONERA a permis de montrer un gain de précision grâce à l’emploi de l’approcheSAS et ce pour un coût de calcul compatible avec un cycle de conception industrielle. / This research work is meant to assess an upgraded URANS approach, namely the Scale-Adaptive Simulation (SAS). This method is similar to a conventional RANS approach (namelythe SSTmodel) in attached areas and is able to adapt the eddy-viscosity level in detached areas toensure the resolution, at least partially, of the turbulent structures. In a first part of this researchwork, an improvement of the SAS approach is suggestedto allowa better sensitivity of themodelto instabilities such as Kelvin-Helmholtz ones. This "improved" model is referred to as SAS-αLmodel. Both SAS and SAS-αL models were implemented in the ONERA Navier-Stokes solverelsA and both of themaswell as the SSTmodelwere tested on academic test cases : a cylinder in acrossflowat a high Reynolds number, a backward-facing step flowcorresponding to theDriver&Seegmiller experiment and the transonic flow over the M219 cavity experimentally investigatedby de Henshaw. The influence of the numerical parameters was deeply investigated and particularattention was paid to the high-order space-discretization schemes effects. The reliabilityof the SAS approach in an industrial framework was assessed on an aeronautic configurationnamely a nacelle de-icing device. Comparisons between the threemodels (SST, SAS and SAS-αL)and an experimental database available at ONERA - The French Aerospace Lab have shown thebetter accuracy of the SAS approach as well as the high potential of the SAS-αL model.

Flow separation and reattachment happens in many fluid mechanical situations occurring in engineering applications as well as in nature. The flow over a backward-facing step represents a geometrically simple flow situation exhibiting both flow separation and reattachment. Broadly speaking there are only two important parameters in the problem, the Reynolds number(Re) based on the step height(h),and a geometrical parameter, referred to as the Expansion ratio(ER), defined as the downstream channel height to the upstream channel height. In spite of the relative simplicity of this geometry, the flow downstream is quite complex. The main focus of the present work is to elucidate the unsteady three-dimensional coherent structures present in this flow at large Re, Re>36,000,based on the step height(h). For this, we use velocity field measurements from Particle Image Velocimetry (PIV)in conjunction with hotwire anemometry measurements. The time-averaged structure of this flow is first studied in detail, including the effect of Reynolds number(Re) and Expansion Ratio(ER), on it. These studies show that at sufficiently large Re (Re>20,000), the reattachment length becomes independent of Re. The detailed internal structure of the separation bubble is also found to be independent of Re, but for Revalues that are relatively larger(Re>36,000). At large Re, the main effect of ER ,is found to be on the reattachment length, which increases with ER and saturates for ER values greater than about 1.8. The detailed internal structure of the separation bubble has been mapped at high Re and is found to be nearly the same for all ER, when the streamwise length is normalized by the reattachment length. In order to elucidate the unsteady coherent vortical structures, PIV measurements are done in two orthogonal planes downstream of the backward-facing step. These measurements are done for ER= 1.50 at large Re(Re=36,000) and in a large aspect ratio facility(AR= span length/step height= 24); the latter being important to avoid any effects due to span-wise confinement. In the spanwise plane parallel to the lower wall(x-z plane),instantaneous velocity fields show counter rotating vortex pairs, which is a signature of the three-dimensional vortical structures in this plane. Using conditional averaging, this counter-rotating vortex pair signature is captured right from upstream of the step, to well after reattachment. Spatial correlations are used to get the length scale of these coherent vortical structures, which varies substantially from the attached boundary layer before separation to the region after reattachment. The variation of these structures in the cross-stream (vertical) direction at reattachment and beyond gives an idea about their three dimensional shape. The circulation of these counter-rotating pairs is measured from the conditionally aver-aged fields, and is found to increase with streamwise distance reaching normalized circulation values (Γ/Uoh) of about 0.5 around reattachment. Velocity spectra downstream of the step show peaks corresponding to both the shear layer frequency(Stsl)and a relatively lower frequency that corresponds to large-scale shedding from the separation bubble (Stb); the latter in particular being quasi-periodic. Small amplitude sinusoidal forcing at the shedding frequency(Stb) is applied close to the step, by blowing and suction, to make the quasi-periodic shedding more regular. Measurements show that this has a very small effect on both the mean separation bubble and on the counter-rotating structures in the x-z plane. This mild forcing however enables phase locked PIV measurements to be made which shows the bubble shedding phenomenon in the cross-stream plane(side view or x-y plane). The phase-averaged velocity fields show significant variations from phase to phase. Although there is some hint of structures being shed, from these phase-averaged fields, it is not very clear. One of the primary reasons is the fact that the flow is effectively spanwise averaged, as the three-dimensional structures are not locked in the spanwise direction. To get a three dimensional view of the sheddin gphenomenon, it is necessary to lock the spanwise location with respect to the three-dimensional vortical structures before averaging across the different phases. We use the condition, u’<- urms, to locate the central plane between the counter-rotating structures, which in effect are the “legs” of the three-dimensional structure. With this condition, we effectively get a slice of the shedding cycle cutting through the “head” of the three-dimensional structure. Apart from this cut, we also get a cut between adjacent structures from the weak sweep events, with the condition u’<- urms. Using these conditions, on the phase-locked velocity fields, we effectively lock the structures in time, as well as in the spanwise direction. With this ,a clearer picture of the shedding process emerges. The flow is highly three-dimensional near reattachment and the shedding of the separation bubble is modulated in the spanwise direction owing to the three-dimensional hairpin like vortical structures in the flow. The separation bubble is seen bulged out and lifted high at locations where the head of the hairpin vortex passes, owing to the strong ejection of fluid caused by the vortical structure. On the other hand, outside the hairpin vortices, weak sweep events push the flow towards the wall and make it shallow and less prominent, with the shedding being very weak in this plane. From these observations, a three-dimensional picture of the flow is proposed.

Les stratégies de contrôle d’écoulement, telles que le soufflage / aspiration, ont prouvé leur efficacité à modifier les caractéristiques d’écoulement à des fins diverses en cas de configurations usuellement simples. Pour étendre cette approche sur des cas industriels, la simulation de dispositifs à échelle réelle et l’optimisation des paramètres de contrôle s’avèrent nécessaires. L’objectif de cette thèse est de mettre en place une procédure d’optimisation pour résoudre cette catégorie de problèmes. Dans cette perspective, l’organisation de la thèse est divisé en trois parties. Tout d’abord, le développement et la validation d’un solveur d’écoulement turbulent compressible instationnaire, résolvant les équations de Navier-Stokes moyennées (RANS) dans le cadre d’une discrétisation mixte de type éléments finis / volumes finis (MEV) sont présentés. Une attention particulière est portée sur la mise en œuvre de modèles numériques de jet synthétique à l’aide de simulations sur une plaque plane. Le deuxième axe de la thèse décrit et valide la mise en œuvre d’une méthode d’optimisation globale basée sur un modèle réduit du type processus gaussien (GP), incluant une approche de filtrage d’erreurs numériques liées aux observations. Cette méthode EGO (Efficient Global Optimization), est validée sur des cas analytiques bruités 1D et 2D. Pour finir, l’optimisation de paramètres de contrôle de jet synthétique sur deux cas test pertinents pour les industriels : un profil d’aile NACA0015, avec objectif de maximiser la portance moyenne et une marche descendante avec objectif de minimiser la longueur de recirculation moyenne. / Active flow control strategies, such as oscillatory blowing / suction, have proved their efficiency to modify flow characteristics for various purposes (e.g. skin friction reduction, separation delay, etc.) in case of rather simple configurations. To extend this approach to industrial cases, the simulation of a large number of devices at real scale and the optimization of parameters are required. The objective of this thesis is to set up an optimization procedure to solve this category of problems. In this perspective, the organization of the thesis is split into three main parts. First, the development and validation of an unsteady compressible turbulent flow solver using the Reynolds-Averaged Navier-Stokes (RANS) using a Mixed finite-Element/finite-Volume (MEV) framework is described. A particular attention is drawn on synthetic jet numerical model implementation by comparing different models in the context of a simulation over a flat plate. The second axis of the thesis describes and validates the implementation of a Gaussian Process surrogate model based global optimization method including an approach to account for some numerical errors during the optimization. This EGO (Efficient Global Optimization) method, is validated on noisy 1D and 2D analytical test cases. Finally, the optimization of two industrial relevant test cases using a synthetic jet actuator are considered: a turbulent flow over a NACA0015 for which the time-averaged lift is regarded as the control criterion to be maximized, and an incompressible turbulent flow over a Backward Facing Step for which the time-averaged recirculation length is minimized.

The main task of the diploma thesis is to use the open areas between the streets Stefanikova, Reissigova, Sportovni and Pionyrská in Brno for creating a multifunctional urban structure with the appropriate functions. Diploma thesis is based on the urban-architectural design created in the previous semester project. Thesis closely addresses the proposed multipurpose building between the streets Stredni a Stankova. In the object is located school of arts, cultural and leisure center, restaurant, café, music club and rentable units. Under the building are designed collective garages.

This thesis describes the design, manufacture and characterisation of thick vacuum plasma sprayed tungsten (W) coatings on steel substrates. Fusion is a potentially clean, sustainable, energy source in which nuclear energy is generated via the release of internal energy from nuclei. In order to fuse nuclei the Coulomb barrier must be breached - requiring extreme temperatures or pressures – akin to creating a ‘star in a box’. Tungsten is a promising candidate material for future fusion reactors due to a high sputtering threshold and melting temperature. However, the large coefficient of thermal expansion mismatch with reactor structural steels such as the low activation steel Eurofer’97 is a major manufacturing and in-service problem. A vacuum plasma spraying approach for the manufacture of tungsten and tungsten/steel graded coatings has been developed successfully. The use of graded coatings and highly textured 3D interface surfi-sculpt substrates has been investigated to allow the deposition of thick plasma sprayed tungsten coatings on steel substrates. Finite element models have been developed to understand the residual stresses that develop in W/steel systems and made use of experimental measurements of coating thermal history during manufacture and elastic moduli measured by nano-indentation. For both the graded and surfi-sculpt coating, the models have been used to understand the mechanism of residual stress redistribution and relief in comparison with simple W on steel coatings, particularly by consideration of stored strain energy. In the case of surfi-sculpt W coatings, the patterned substrate gave rise to regular stress concentrating features, and allowed 2mm thick W coatings to be produced reproducibly without delamination. Preliminary through thickness residual stress measurements were compared to model predictions and provided tentative evidence of significant W coating stress relief by regulated coating segmentation.

This work develops a discontinuous Galerkin finite element discretization of non- linear hyperbolic conservation equations with efficient and robust high order stabilization built on an entropy-based artificial viscosity approximation. The solutions of equations are represented by elementwise polynomials of an arbitrary degree p > 0 which are continuous within each element but discontinuous on the boundaries. The discretization of equations in time is done by means of high order explicit Runge-Kutta methods identified with respective Butcher tableaux. To stabilize a numerical solution in the vicinity of shock waves and simultaneously preserve the smooth parts from smearing, we add some reasonable amount of artificial viscosity in accordance with the physical principle of entropy production in the interior of shock waves. The viscosity coefficient is proportional to the local size of the residual of an entropy equation and is bounded from above by the first-order artificial viscosity defined by a local wave speed. Since the residual of an entropy equation is supposed to be vanishingly small in smooth regions (of the order of the Local Truncation Error) and arbitrarily large in shocks, the entropy viscosity is almost zero everywhere except the shocks, where it reaches the first-order upper bound. One- and two-dimensional benchmark test cases are presented for nonlinear hyperbolic scalar conservation laws and the system of compressible Euler equations. These tests demonstrate the satisfactory stability properties of the method and optimal convergence rates as well. All numerical solutions to the test problems agree well with the reference solutions found in the literature. We conclude that the new method developed in the present work is a valuable alternative to currently existing techniques of viscous stabilization.

The subject of the diploma thesis is to design a project study and a building program that would become a compromise between the requirements of the city of Brno and BUT in the area of Kraví hora in the Brno city center. The city of Brno would like to transform the area into a public park. But BUT considers it as its "family silver" because they realize its extraordinary value. Options of a constructions are really limited because of many area regulations. My proposal counts on the demolition of all existing buildings in the area, respects property area relations , protection zone, continuity with existing traffic roads, height regulation, imaginary raster of surrounding buildings, slope of terrain and orientation to the cardinal points. My suggest represents a study of five groups of objects which creating a rectangular raster. As a compromise solution, I chose the presentation and promotional areas of the individual faculties of BUT for the content of the buildings. Faculties have spaces for hobby groups for the public comprise all age groups included. I also designed the BUT Museum of History, a multimedia hall, a cafeteria, studios, a student leisure center and an observation tower with a climbing wall.