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International audience; Anaerobic digestion is a widely used process for waste treatment and energy production. This natural process takes place in a controlled environment, anaerobic digesters. Mixing is one of the main operating parameters. The understanding of the flows during the agitation of the medium is crucial for the optimization of the process yield. In fact, the mass and heat transfers are enhanced by the agitation. However, the complex biochemical reactions can be inhibited with overly vigorous agitation. A detailed and in-depth understanding of the phenomena occurring during agitation requires modeling studies. In this chapter, we propose a general approach, based on computational fluid mechanics (CFD), to analyze the mechanical mixing of an anaerobic reactor. We apply this work to the anaerobic digestion of the sugarcane vinasse, which is a liquid waste generated during the production of alcohol. The single-phase Reynolds-averaged Navier-Stokes (RANS) simulations of mechanical agitation of Newtonian fluids for different rotational speeds are presented. The equations system is closed with the standard k-epsilon turbulence model. The flow field is analyzed with the velocity profiles, the Q and Lambda2 fields, the pressure and the vorticity.

International audience; This paper deals with a multi-objective topology optimization problem in an asymmetrically heated channel, based on both pressure drop minimization and heat transfer maximization. The problem is modeled by assuming steady-state laminar natural convection f low. The incompressible Navier-Stokes equations coupled with the convection-diffusion equation, under the Boussinesq approximation, are employed and are solved with the finite volume method. In this paper, we discuss some limits of classical pressure drop cost function for buoyancy driven flow and, we then propose two new expressions of objective functions: the first one takes into account work of pressure forces and contributes to the loss of mechanical power while the second one is related to thermal power and is linked to the maximization of heat exchanges. We use the adjoint method to compute the gradient of the cost functions. The topology optimization problem is first solved for a Richardson (Ri) number and Reynolds number (Re) set respectively to Ri ∈ {100,200,400} and Re = 400. All these configuration are investigated next in order to demonstrate the efficiency of the new expressions of cost functions. We compare two types of interpolation functions for both the design variable field and the effective diffusivity. Both interpolation techniques have pros and cons and give slightly the same results. We notice that we obtain less isolated solid elements with the sigmoid type interpolation functions.Then, we choose to work with the sigmoid and solve the topology optimization problem in case of pure natural convection, by setting Rayleigh number to {3×103,4×104,5×105}. In all considered cases, our algorithm succeeds to enhance one of the phenomenon modeled by the proposed cost functions without deteriorating the other one. The optimized design obtained suppresses any reversal flow at the exit of the channel. We also show that the thermal exchanges are improved by computing the Nusselt numbers and bulk temperature. We conclude that the new expressions of objective functions are well suited to deal with natural convection optimization problem in a vertical channel.

International audience; Several engineering problems result in a PDE-constrained optimization problem that aims at finding the shape of a solid inside a fluid which minimizes a given cost function. These problems are categorized as Topology Optimization (TO) problems. In order to tackle these problems, the solid may be located with a penalization term added in the constraints equations that vanishes in fluid regions and becomes large in solid regions. This paper addresses a TO problem for anisothermal flows modelled by the steady-state incompressible Navier-Stokessystem coupled to an energy equation, with mixed boundary conditions, under the Boussinesq approximation. We first prove the existence and uniqueness of a solution to these equations as well as the convergence of its finite element discretization. Next, we show that our TO problem has at least one optimal solution for cost functions that satisfy general assumptions. The convergence of discrete optimum toward the continuous one is then proved as well as necessary first order optimality conditions. Eventually, all these results let us design a numerical algorithm to solve a TO problem approximating solids with piecewise constant thermal diffusivities also refered as multi-materials. A physical problem solved numericallyfor varying parameters concludes this paper.

International audience; This paper deals with the finite element approximation of the Darcy-Brinkman-Forchheimer equation, involving a porous media with spatially-varying porosity, with mixed boundary condition such as inhomogeneous Dirichlet and traction boundary conditions. We first prove that the considered problem has a unique solution if the source terms are small enough. The convergence of a Taylor-Hood finite element approximation using a finite element interpolation of the porosity is then proved under similar smallness assumptions. Some optimal error estimates are next obtained when assuming the solution to the Darcy-Brinkman-Forchheimer model are smooth enough. We end this paper by providing a fixed-point method to solve iteratively the discrete non-linear problems and with some numerical experiments to make more precise the smallness assumptions on the source terms and to illustrate the theoretical convergence results.

The objective of this study is to highlight the effect of porosity variation in a topology optimization process in the field of fluid dynamics. Usually a penalization term added to momentum equation provides to get material distribution. Every time material is added inside the computational domain, there is creation of new fluid-solid interfaces and apparition of gradient of porosity. However, at present, porosity variation is not taken account in topology optimization and the penalization term used to locate the solid is analogous to a Darcy term used for flows in porous media. With that in mind, in this paper, we first develop an original one-domain macroscopic model for the modelling of flow through spatially varying porous media that goes beyond the scope of Darcy regime. Next, we numerically solve a topology optimization problem and compare the results obtained with the standard model that does not include effect of porosity variation with those obtained with our model. Among our results, we show for instance that the designs obtained are different but percentages of reduction of objective functional remain quite close (below 4\% of difference). In addition, we illustrate effects of porosity and particle diameter values on final optimized designs.

This paper proposes a new interpolation technique based on density approach to solve topology optimization problems for heat transfer. Natural convection forces are dominated as Richardson number is equal to 2.8. Problems are modeled under the assumptions of steady-state laminar flow using the incompressible Navier–Stokes equations coupled to the convection-diffusion equation through the Boussinesq approximation. The governing equations are discretized using finite volume elements and topology optimization is performed using adjoint sensitivity analysis. Material distribution and effective conductivity are interpolated by two sigmoid functions respectively hτ(α) and kτ(α) in order to provide a continuous transition between the solid and the fluid domains. Comparison with standard interpolation function of the literature (RAMP function) shows a smaller transition zone between the fluid and the solid thereby, avoiding some regularization techniques. In order to validate the new method, numerical applications are investigated on some geometric configurations from the literature, namely the single pipe and the bend pipe. Lastly, as two new parameters are introduced thanks to the interpolation functions, we study their impact on results of the optimization problem. The study shows that the proposed technique is a viable approach for designing geometries and fluid-porous media interfaces are well-defined.

Submitted to Energy and Buildings; Safety performance is one of the most important considerations in building design. Moreover, new environmental building design allows construction to have a sustainable relationship with the outdoor climate, especially in tropical context. This paper aims at evaluating how conception that allows natural ventilation by mean of passive strategies, affects fire safety performance in buildings. A methodology, combining safety and comfort through a global index, is proposed in order to understand how the consideration of fire safety can affect initial passive design. The use of dynamic thermal simulation associated with fire simulation gives the opportunity to quantify fire performance annually. Sensitivity analysis is performed by using delta moment index. This allows to evaluate the absolute impact of input parameter on both fire safety and thermal comfort outputs. A refined study is then performed by the use of conditional output distribution. It takes into account the relative importance given to fire Safety or thermal comfort concerns. The strong dependence of fire safety, in terms of smoke extraction, on weather conditions, building orientation, occupation profiles and seasons, is demonstrated in naturally ventilated buildings.

This article consists in a numerical study of the influence of thermal stratification and surface radiation on laminar airflow induced by natural convection in vertical, asymmetrically heated chann...

The aim of this report is to present a model of a rigid-rotor system based on computational fluid dynamics (CFD), which is applied on a vertical axis wind turbine (VAWT) research. Its originality results from the use of the average value of the variable rotational speed method taken in a periodic steady-state (PSS) of the VAWT rotor instead of the classical fixed rotational speed method. This approach was chosen in order to determine the mechanical and aerodynamic parameters of the wind turbine. The modeling method uses an implicit Euler iterative solution strategy, which resolves the coupling between fixed and moving rotor domains. The main methods that were adopted are based on the three-dimensional modeling of the interaction of the fluid flow with a rigid-rotor. The strategy consists of using the Reynolds averaged Navier Stokes (RANS) equations with the standard k- ϵ and SST k- ω models to solve the fluid flow problem. To perform the rigid-rotor motion in a fluid, the one degree of freedom (1-DOF) method was applied. In the present study, the steady-state and dynamic CFD simulations of the Savonius rotor are adopted to contribute to the validation elements of the VAWT models that are used. The dynamic study allows the investigation of the rotor behavior and the relation between velocity, pressure, and vorticity fields in and around the rotor blades. The flow fields generated by the rotation of the Savonius rotor were investigated in the half revolution period of the rotor angle θ from 0° to 180°. In this range of θ, the focus is on generating and dissipating vortices.Copyright © 2013 John Wiley & Sons, Ltd.

International audience

International audience; In order to provide comfort in a low energy consumption building, it is preferable to use natural ventilation rather than HVAC systems. To achieve this, engineers need tools that predict the heat and mass transfers between the building's interior and exterior. This article presents a method implemented in some building software, and the results are compared to CFD. The results show that the knowledge model is not sufficiently well-described to identify all the physical phenomena and the relationships between them. A model is developed which introduces a new building-dependent coefficient allowing the use of Walton's model, as extended by Roldan to large external openings, and which better represents the turbulent phenomena near large external openings. The formulation of the mass flow rates is inversed to identify modeling problems. It appears that the discharge coefficient is not the only or best parameter to obtain an indoor static pressure compatible with CFD results, or to calculate more realistic mass flow rates.

The present paper is concerned with the results of the numerical investigation of unpermanent laminar, natural convection in an asymmetrically heated inclined open channel ( i = 0,45,60 and 75 ∘ ) with walls at uniform heat flux ( q w = 10,50,75 and 100 W m −2 ). Two methodological approaches have been adopted to investigate the air flow in these configurations: 2D and 3D description, and four sets of inlet-outlet velocity-pressure boundary conditions have been considered. Significant differences are observed in the flow dynamics between 2D and 3D results. The numerical results are compared with the experimental data and a good agreement is obtained when a local pressure boundary condition is applied at the inlet/outlet sections in the 3D case. A generalized correlation for the average Nusselt number is then obtained from numerical results. This correlation covers a wide range of the modified Rayleigh number and aspect ratio values ( Ra m cos( i ) varying from 1.71 × 10 4 to 3.60 × 10 6 and 6.5 H / b

The paper deals with the optimization of building energy efficiency in tropical climates by reducing the period of air-conditioning thanks to natural ventilation and a better bioclimatic design. A bioclimatic approach to designing comfortable buildings in hot and humid tropical regions requires, firstly, some preliminary, important work on the building envelope to limit the energy contributions, and secondly, an airflow optimization based on the analysis of natural ventilation airflow networks. For the first step, tools such as nodal or zonal models have been largely implemented in building energy codes to evaluate energy transport between indoor and outdoor. For the second step, the assessment of air velocities, in three dimensions and in a large space, can only be performed through the use of detailed models such as with CFD. A new modelling approach based on the derivation of a new quantity—i.e. the well-ventilated percentage of a living space is proposed. The well-ventilated percentage of a space allows a time analysis of the air motion behaviour of the building in its environment. These percentages can be over a period such as 1 day, a season or a year. Twelve living spaces with different configuration of openings have been studied to compare the performance of ventilation function of the opening distribution. Results and discussion are presented in the paper. This method is helpful for an architect to design the rooms according to their use, and their environment. Finally, the developed models can be used in building projects to estimate the period of the natural ventilation and to reduce the energy consumption due to air-conditioning.

International audience; The present study deals with the analysis of the transient forces of a Savonius vertical axis wind turbine (VAWT) using computational fluid dynamics (CFD). Unsteady, Reynolds Averaged Navier-Stokes CFD simulations were conducted using two different rotors and two simulation methodologies. The first rotor had an aspect ratio of 1.1 and simulations were conducted by incorporating the dynamic equations of the rigid-rotor motion using a one degree-of-freedom (1-DOF) module to evaluate the rotor's free motion. The second rotor had an aspect ratio of 0.7 and simulations were conducted by specifying a fixed rotational velocity. The predicted torque and power curves were validated using experimental data. The transient forces from the two rotor blades, the resultant forces, and the longitudinal drag and lateral lift coefficients were evaluated using the two complementary data sets. The lateral force coefficient had a large contribution to the rotor torque at low azimuth angles and at low tip speed ratios (λ). At tip speed ratios above 0.6, the effect of the longitudinal drag force on the rotor operation increased and the lateral lift force contribution decreased. The resultant force angle was shown to become more acute due to the increase in the longitudinal force with increasing λ.

International audience; Comparison exercises have been carried out by different research teams to study the sensitivity of the natural convection occurring in a vertical asymmetrically heated channel to four sets of open boundary conditions. The dimensionless parameters have been chosen so that a return flow exists at the outlet. On the whole, results provided by the partners are in good agreement; benchmark solutions are then defined for each of the boundary conditions. Whilst the local and average Nusselt numbers based on the entrance temperature do not depend much on conditions applied in the aperture sections, the net fluid flow rates crossing the channel and the characteristics of the recirculation cells are highly influenced. But we proved that these modifications of flow patterns do not alter significantly the fluid flow rates leaving the channel through the exit section.

International audience; Presentation about The test case ADNBATI, a benchmark on natural ventilation in a room

International audience; The Savonious rotor is a slow running vertical axis wind turbine (VAWT) which gets stabilized after a certain period of functioning. This work aims to assess the results of an aerodynamic study concerning a Savonious rotor. The computational fluid dynamics (CFD) is a technique used to solve the airflow around the wind turbine rotor. In this paper, the turbulence models standard k-ε and shear stress transport (SST) k-co are the turbulences models. A three-dimensional study of the problem has been conducted. Firstly, the moment of static forces acting on the rotor blades have been compared to with experimental results. Secondly, the integration of the equation of motion of the Savonious rotor with one degree of freedom (1-DOF) rigid body dynamics model. Implicit schemes for unsteady Euler equations have been used to perform dynamic simulation.

p6; International audience; This paper presents a numerical investigation of airflow in an open geometry. The case under consideration is a room with two opposite and decentred openings which create a strong potential for ventilation. The building's characteristic dimensions are the following: H=2.50 m height and W=6.50 m width. A temperature difference between the walls and the outside air is fixed, resulting in a characteristic Rayleigh number (Ra) ranging from 105 to 107. This room model proceeds from a benchmark exercise "ADNBATI" (http ://adnbati.limsi.fr) coordinated by the"Centre National de la Recherche Française -CNRS-".

International audience; Solar cooling applied to buildings is without a doubt an interesting alternative for reducing energy consumption in traditional mechanical steam compression air conditioning systems. The study of these systems should have a closely purely fundamental approach including the development of numerical models in order to predict the overall installation performance. The final objective is to estimate cooling capacity, power consumption, and overall installation performance with relation to outside factors (solar irradiation, outside temperature...). The first stage in this work consists of estimating the primary energy produced by the solar collector field. The estimation of this primary energy is crucial to ensure the evaluation of the cooling capacity and therefore the cooling distribution and thermal comfort in the building. Indeed, the absorption chiller performance is directly related to its heat source. This study presents dynamic models for double glazing solar collectors and compares the results of the simulation with experimental results taken from our test bench (two collectors). In the second part, we present an extensive collector field model (36 collectors) from our solar cooling installation at The University Institute of Technology in St Pierre, Reunion Island as well as our stratified tank storage model. A comparison of the simulation results with real scale solar experimental data taken from our installation enables validation of the double glazing solar collector and stratified tank dynamic models.

International audience; Presentation about Ensuring desired natural ventilation rate by means of optimized openings

In this paper, emphasis is put on the design of a neural network (NN) to model the direct solar irradiance. Since, unfortunately, a neural network is not a statistician-in-a-box, building a NN for a particular problem is a nontrivial task. As a consequence, we argue that in order to properly model the direct solar irradiance, a systematic methodology must be employed. For this purpose, we propose a two-step approach to building the NN model. The first step deals with a probabilistic interpretation of the NN learning by using Bayesian techniques. The Bayesian approach to modeling offers significant advantages over the classical NN learning process. Among others, one can cite (i) automatic complexity control of the NN using all the available data and (ii) selection of the most important input variables. The second step consists of using a new sensitivity analysis-based pruning method in order to infer the optimal NN structure. We show that the combination of the two approaches makes the practical implementation of the Bayesian techniques more reliable.

In detailled buiding simulation models, airflow modelling and solving are still open and crucial problems, specially in the case of open buildings as encountered in tropical climates. As a consequence, wind speed conditioning indoor thermal comfort or energy needs in case of air conditionning are uneasy to predict. A first part of the problem is the lack of reliable and usable large opening elementary modelling and another one concerns the numerical solving of airflow network. This non linear pressure system is solved by numerous methods mainly based on Newton Raphson (NR) method. This paper is adressing this part of the difficulty, in our software CODYRUN. After model checks, we propose to use Picard method (known also as fixed point) to initialise zone pressures. A linear system (extracted from the non linear set of equations) is solved around 10 times at each time step and NR uses this result for initial values. Known to be uniformly but slowly convergent, this method appears to be really powerful for the building pressure system. The comparison of the methods in terms of number of iterations is illustrated using a real test case experiment., Comment: IASTED Modelling and Simulation Conference (MS0 2005), Orangestad : Aruba (2005)

International audience; Controlling humidity to prevent moisture and condensation phenomena is a growing problem for building designers nowadays. Ventilation and air conditioning are common solutions to avoid mold and condensation. However, to promote low cost energy buildings, an alternate solution may be to decrease the daily variation of humidity with anti fungi treated absorbing material. In this case, a very accurate evaluation of room humidity is necessary to determine material ability to buffer moisture. This paper briefly presents a model of moisture transfer between room air and walls for tropical climates. This model includes hygroscopic and nonhygroscopic wall behavior. The aim of the model is to calculate the water quantities buffered by walls and thus better evaluate room moisture. A validation of the model is presented consisting of a sensitivity analysis and an experimental comparison. The experiments carried out in a test cell are described. An application of the model is also proposed to tackle mold presence with various absorbing materials located in a tropical humid environment.

The aim of this paper is to show the influence of the atmospheric boundary layer profile on the distribution of velocity in a building having two large openings. The knowledge of the flow form inside a building is useful to define a thermal environment favourable with thermal comfort and good air quality. In computational fluid dynamics, several profiles of atmospheric boundary layer can be used like logarithmic profiles or power profiles. This paper shows the impact of these profiles on the indoor airflow. Non-ventilated or ventilated parts of room are found. They show respectively ineffective ventilation and effective ventilation. A qualitative and global approach allows to observe the flows in a cubic building and to show the influence of each profile according to the external ground roughness and the incidence angle of the wind. Some zones, where occupants move, are named volumes of life. Ventilation is there observed using traditional tools in order to analyze quantitatively the ventilation of these zones., Ninth International IBPSA Conference, Montr\'eal : Canada (2005)

International audience; This paper presents the coupling of a building thermal simulation code with genetic algorithms (GAs). GAs are randomized search algorithms that are based on the mechanisms of natural selection and genetics. We show that this coupling allows the location of defective sub-models of a building thermal model i.e. parts of model that are responsible for the disagreements between measurements and model predictions. The method first of all is checked and validated on the basis of a numerical model of a building taken as reference. It is then applied to a real building case. The results show that the method could constitute an efficient tool when checking the model validity.

Summary: Corynebacterium sp. XG is a facultative methylotroph. Determination of the activities of several enzymes and use of mutants unable to grow on methanol indicated that in this Gram-positive strain methanol was metabolized through the serine pathway. Synthesis of the enzymes of this pathway was induced when cells were grown in the presence of methanol or its catabolic products.

International audience; A simplified model of indoor short wave radiation couplings adapted to multi-zone simulations is proposed, thanks to a simplifying hypothesis and to the introduction of an indoor short wave exchange matrix. The specific properties of this matrix appear useful to quantify the thermal radiation exchanges between the zones separated by windows or large openings. Integrated in CODYRUN software, this module is detailed and compared to experimental measurements carried out on a real scale tropical building

International audience; In tropical context and particularly in Reunion Island, promoting passive design is compulsory, but cannot be achieved without considering fire safety. This article aims at evaluating the interactions that exist between fire safety and thermal comfort in buildings, using variance based and moment independent methods. Two stategies are proposed: a first one, dissociated, where fire safety assessment and thermal comfort are evaluated separately and a second combining both considerations. Input parameters that influence the most the selected output indices are investigated for each strategy. A normalized index combining thermal comfort and fire safety is suggested introducing a new methodology. Difference between the two strategies is highlighted.

This paper presents a zero energy project -ie ZEN applied to a university building in Reunion Island. The construction work will begin in September 2006 and will last one year. The aim is to create a building which uses half the energy of a standard building. The methodology was conceived to meet requirements defined during the thermal design and building systems planning stage. Innovations relating to architectural design, building systems performance and numerical simulation are presented. Solar panels integrated into the roofing provide sufficient electrical energy for the building to produce more energy than it uses.Copyright © 2006 by ASME

Context: Air-conditioning represents a high-energy expenditure in the sector of the building, which could be reduced drastically through the use of passive cooling systems. In hot and humid climates, the passive cooling of premises is a tried and tested technique ordained around four principles: to minimize the external and internal heat transfers, to bring inertness to the building, to humidify the air, and to ensure a good convection in order to favor convective exchanges. Objective: The description of thermo-convective transfers (estimation of mass flows rate and heat transfers) set in open cavities (rooms with crossing ventilation, solar chimney, outer skin of a double facade,...) is still relatively uncommon and the stakes are high to improve passive systems. The study of these phenomena can be evaluated through computational fluid dynamics. This thesis’s objectives are to achieve precise numerical simulations of airflow inspecific configurations of passive systems in damp tropical climates, in order to improve and deepen our knowledge of natural convection and to begin to give information concerning the choice of numerical boundary conditions to apply to open geometries.Numerical approach: The numerical approach adopted in this work, to study the natural turbulent convection, is the Large-Eddy Simulation. This approach is halfway between a direct numerical simulation and Reynolds-averaged Navier–Stokes equations. Such a technique is advantageous as it leads to a necessary substantial reduction of the number of discretizationpoints compared to the technique of direct simulation requirements, while retaining the dynamic aspect of the flows. Results: The results obtained in this work refer to the study of the dynamic boundary conditions to impose in open geometries with SND and to the application of the LES to different configurations of open cavities with a turbulent flow, in order to characterize temperature and velocity fields and then deduce mass flow rate, enthalpy flow,... The results have been compared either to other numerical results in the framework of national benchmarks (benchmark AmeThand ADNBâti) or to experimental results., Contexte du sujet : La climatisation est un poste de dépense énergétique important dans le secteur du bâtiment, qui pourrait être réduit de manière drastique par l’utilisation de systèmes passifs de rafraîchissement. Dans les climats chauds et humides, le rafraîchissement passif des bâtiments est une solution éprouvée, qui s’ordonne autour de quatre principes : minimiser les apports de chaleur interne et externe, apporter de l’inertie au bâtiment, humidifier l’air et assurer une bonne ventilation pour favoriser les échanges convectifs. Objectifs : La description des transferts thermo-convectifs (évaluation des débits massiques, des transferts de chaleur) mis en jeu dans des cavités ouvertes (pièces avec ventilation traversante, cheminées solaires, doubles peaux, espaces sous-toiture) est encore mal connue et constitue un enjeu pour l’amélioration des systèmes passifs. L’étude de ces phénomènes peut être évaluée par la mécanique des fluides numérique. Les objectifs de ce travail de thèse sont : de réaliser des simulations numériques fines du comportement thermo-aéraulique dans des configurations typiques de systèmes passifs en climat tropical humide, afin d’améliorer nos connaissances sur la ventilation naturelle, d’approfondir et d’apporter des éléments de réponses en ce qui concerne le choix des conditions limites numériques à appliquer pour les systèmes ouverts. Modélisation numérique : L’approche numérique adoptée dans ce travail, pour étudier la convection naturelle turbulente, est la simulation des grandes échelles (SGE ou LES en anglais). Cette approche se situe à mi-parcours entre la méthode de calcul direct et la résolution des équations moyennées en temps, de type RANS. L’avantage d’une telle technique est la réduction appréciable du nombre de points de discrétisation nécessaire par rapport à celui exigé par la méthode de calcul direct, tout en conservant l’aspect dynamique des écoulements. Résultats : Les résultats obtenus lors de ce travail concernent l’étude des conditions limites dynamiques à imposer pour des géométries ouvertes avec une SND et l’application de la SGE à différentes configurations de cavités ouvertes en régime turbulent, afin de caractériser les champs de température et de vitesse et d’en déduire les grandeurs intégrales d’intérêt (débit massique, débit enthalpique, renouvellement d’air,... ). Les résultats de ces calculs ont été comparés soit à d’autres résultats numériques dans le cadre de benchmarks nationaux (benchmark numérique AmeTh et ADNBâti) ou à des résultats expérimentaux.

Flow and mass transport through porous media are an important part of underground water studies. Pollution spreading or salt water intrusion in coastal groundwater tables are well known applications. This thesis manuscript is dedicated to the study of this physical phenomena through numerical modelling. Different finite element methods are presented and discussed. We focus on the mathematical representation of strongheterogeneous and anisotropic porous media. We introduce two new numerical methods named H-RTm and H-RTp methods. They take advantage of the hybridization technique applied to mixed finite element methods and discontinuous Galerkin finite element methods. The benefits reached in the numerical representation of flow and mass transfer in porous media are illustrated through numerical examples currently used in literature.; La représentation des écoulements et du transport de masse en milieu poreux trouve des applications diverses en hydrogéologie dont notamment l’étude de la propagation des polluants dans les sols ou encore l’étude des transferts d’eau salée dans les nappes phréatiques côtières. Ce manuscrit de thèse propose donc d’étudier ces phénomènes physiques à travers la modélisation numérique. Plusieurs ensembles de méthodes d’éléments finis sont présentées et discutées. L’accent est essentiellement mis sur la représentation mathématique des milieux fortement hétérogènes et anisotropes. Deux nouvelles méthodes de résolution numérique sont ainsi introduites, à savoir les méthodes H-RTm et H-RTp. Ces méthodes sont toutes deux issues de la technique d’hybridation appliquée aux éléments finis mixtes et aux éléments finis discontinus de Galerkin. Les bénéfices qu’elles apportent dans la représentation des phénomènes d’écoulement et de transport de masse en milieu poreux sont alors illustrés à travers des exemples numériques retrouvés dans la littérature.

Flow and mass transport through porous media are an important part of underground water studies. Pollution spreading or salt water intrusion in coastal groundwater tables are well known applications. This thesis manuscript is dedicated to the study of this physical phenomena through numerical modelling. Different finite element methods are presented and discussed. We focus on the mathematical representation of strongheterogeneous and anisotropic porous media. We introduce two new numerical methods named H-RTm and H-RTp methods. They take advantage of the hybridization technique applied to mixed finite element methods and discontinuous Galerkin finite element methods. The benefits reached in the numerical representation of flow and mass transfer in porous media are illustrated through numerical examples currently used in literature., La représentation des écoulements et du transport de masse en milieu poreux trouve des applications diverses en hydrogéologie dont notamment l’étude de la propagation des polluants dans les sols ou encore l’étude des transferts d’eau salée dans les nappes phréatiques côtières. Ce manuscrit de thèse propose donc d’étudier ces phénomènes physiques à travers la modélisation numérique. Plusieurs ensembles de méthodes d’éléments finis sont présentées et discutées. L’accent est essentiellement mis sur la représentation mathématique des milieux fortement hétérogènes et anisotropes. Deux nouvelles méthodes de résolution numérique sont ainsi introduites, à savoir les méthodes H-RTm et H-RTp. Ces méthodes sont toutes deux issues de la technique d’hybridation appliquée aux éléments finis mixtes et aux éléments finis discontinus de Galerkin. Les bénéfices qu’elles apportent dans la représentation des phénomènes d’écoulement et de transport de masse en milieu poreux sont alors illustrés à travers des exemples numériques retrouvés dans la littérature.

This thesis work presents deals with the issue of fire safety consideration in naturally ventilated buildings. The particular case of the interaction between the wind and hot smoke movement is pinpointed. In the first chapter, basics of natural ventilation mechanisms are shown. Then, the analysis of building’s regulations, relating to fire safety and thermal comfort, allows to highlight potential conflicts and normative gaps. Theses gaps and conflicts are illustrated through real buildings feedbacks. The challenge of indoor flow pattern studies for safety purpose is hence underline. In the second chapter, scientific’s barriers in relation with the transitions between existing flow pattern, when wind and buoyancy are opposed, are identified thought a literature review. A scaled experiment is proposed in the third chapter, using density difference between air and helium, to identify internal flow pattern when wind opposes buoyancy. Three stable internal flow patterns are identified. A power law characterizing the transitions between identified flow pattern, involving source Froude number and dynamic pressure ratio between source jet and wind, is found. In the fourth chapter, the identified flow pattern are observed when the tested volume is emptied, and a relation between the initial Richardson number Ri and the characteristic emptied time θ is found. Furthermore, specific behaviour of internal flow, when the volume is emptied, is quantitatively study thanks to a numerical model. In the last part of this thesis, transitions law between internal flow patterns allows to introduce a new wind dependent fire safety index. A methodology is then proposed to both analyse fire safety and thermal comfort in building. The presented method gives the opportunity to avoid conception conflicts underlined in the first chapter of the present work.; Ces travaux de thèse, répondent à la problématique liée à la sécurité incendie des bâtiments ventilés naturellement, et notamment au comportement des fumées chaudes lorsqu’elles interagissent avec le vent. Le premier chapitre concerne la mise en exergue de la problématique bâtimentaire, au travers de la présentation des moteurs de la ventilation naturelle, d’une analyse règlementaire croisée sécurité incendie / confort thermique, et de multiples retours d’expériences. La nécessité d’étudier les régimes d’écoulement interne lorsque le vent interagit avec la fumée est mise en évidence. Ainsi, dans le second chapitre, les verrous scientifiques, associés à l’identification des régimes d’écoulement en convection mixte, sont soulevés à l’aide d’une analyse de la littérature. Dans le troisième chapitre, nous nous intéressons à la caractérisation des régimes d’écoulement internes lorsque le vent oppose le tirage thermique dans un volume contenant une source constante générant les forces de flottabilité. Une expérimentation densimétrique, air/hélium, à échelle réduite est proposée. Trois régimes d’écoulement internes stables sont mis en évidence. Les transitions entre ces régimes sont caractérisées par une loi puissance, mettant en jeu le nombre de Froude, relatif à la source générant les forces de flottabilité, et le rapport entre la pression dynamique de la source et celle du vent. Dans le quatrième chapitre, ces régimes sont également identifiés, expérimentalement et numériquement, lors de la vidange de fluide léger lorsque le vent oppose le tirage thermique. Une relation entre le nombre de Richardson et un temps de vidange caractéristique est identifiée. L’étude numérique nous permet d’analyser des dynamiques particulières de vidange de manière quantitative. Dans la dernière partie, les lois de transitions entre régimes d’écoulement permettent d’introduire un indicateur de sécurité dépendant des conditions de vent. Une méthode d’analyse, qui considère à la fois la sécurité et le confort, est alors proposée pour éviter les conflits mis en avant dans les retours d’expériences du chapitre 1.

This thesis work presents deals with the issue of fire safety consideration in naturally ventilated buildings. The particular case of the interaction between the wind and hot smoke movement is pinpointed. In the first chapter, basics of natural ventilation mechanisms are shown. Then, the analysis of building’s regulations, relating to fire safety and thermal comfort, allows to highlight potential conflicts and normative gaps. Theses gaps and conflicts are illustrated through real buildings feedbacks. The challenge of indoor flow pattern studies for safety purpose is hence underline. In the second chapter, scientific’s barriers in relation with the transitions between existing flow pattern, when wind and buoyancy are opposed, are identified thought a literature review. A scaled experiment is proposed in the third chapter, using density difference between air and helium, to identify internal flow pattern when wind opposes buoyancy. Three stable internal flow patterns are identified. A power law characterizing the transitions between identified flow pattern, involving source Froude number and dynamic pressure ratio between source jet and wind, is found. In the fourth chapter, the identified flow pattern are observed when the tested volume is emptied, and a relation between the initial Richardson number Ri and the characteristic emptied time θ is found. Furthermore, specific behaviour of internal flow, when the volume is emptied, is quantitatively study thanks to a numerical model. In the last part of this thesis, transitions law between internal flow patterns allows to introduce a new wind dependent fire safety index. A methodology is then proposed to both analyse fire safety and thermal comfort in building. The presented method gives the opportunity to avoid conception conflicts underlined in the first chapter of the present work., Ces travaux de thèse, répondent à la problématique liée à la sécurité incendie des bâtiments ventilés naturellement, et notamment au comportement des fumées chaudes lorsqu’elles interagissent avec le vent. Le premier chapitre concerne la mise en exergue de la problématique bâtimentaire, au travers de la présentation des moteurs de la ventilation naturelle, d’une analyse règlementaire croisée sécurité incendie / confort thermique, et de multiples retours d’expériences. La nécessité d’étudier les régimes d’écoulement interne lorsque le vent interagit avec la fumée est mise en évidence. Ainsi, dans le second chapitre, les verrous scientifiques, associés à l’identification des régimes d’écoulement en convection mixte, sont soulevés à l’aide d’une analyse de la littérature. Dans le troisième chapitre, nous nous intéressons à la caractérisation des régimes d’écoulement internes lorsque le vent oppose le tirage thermique dans un volume contenant une source constante générant les forces de flottabilité. Une expérimentation densimétrique, air/hélium, à échelle réduite est proposée. Trois régimes d’écoulement internes stables sont mis en évidence. Les transitions entre ces régimes sont caractérisées par une loi puissance, mettant en jeu le nombre de Froude, relatif à la source générant les forces de flottabilité, et le rapport entre la pression dynamique de la source et celle du vent. Dans le quatrième chapitre, ces régimes sont également identifiés, expérimentalement et numériquement, lors de la vidange de fluide léger lorsque le vent oppose le tirage thermique. Une relation entre le nombre de Richardson et un temps de vidange caractéristique est identifiée. L’étude numérique nous permet d’analyser des dynamiques particulières de vidange de manière quantitative. Dans la dernière partie, les lois de transitions entre régimes d’écoulement permettent d’introduire un indicateur de sécurité dépendant des conditions de vent. Une méthode d’analyse, qui considère à la fois la sécurité et le confort, est alors proposée pour éviter les conflits mis en avant dans les retours d’expériences du chapitre 1.

This thesis deals with topology optimization of mass and heat transfer in the framework of the vertical asymetrically-heated channel. The incompressible Navier-Stokes equations coupled to the convection-diffusion equation through the Boussinesq approximation are employed and are solved with the finite volume method. We first propose a new interpolation technique for heat transfer optimization and validate it on referenced cases such as the "single pipe" and the "bend pipe". This new technique consists in the introduction of sigmoid interpolation functions to obain a better definition of the interface between fluid and solid domains, during the optimization process. We study then physical phenomenon in the asymmetrically heated channel , in particular the influence of thermal stratification outside the channel and surface radiation on thermal and dynamic quantities. We thus highlight the size variation of reversed flow at the exit of the channel and the plug-effect linked on external thermal stratification. Finally, we propose a new expression of mechanical power in order to control charges losses (despite addition of material) in the vertical channel combined with the expression of thermal power. In all considered cases, our algorithm succeeds to enhance one of the phenomenon modelled by our new cost functions without deteriorating the other one. We also compare the values of standard cost functions from the litterature over iteration of our optimization algorithm and show that our new cost functions are effective.; Les présents travaux de thèse envisagent une nouvelle technique d'optimisation au sens topologique dans des géométries de type canal vertical où se réalisent des transferts de chaleur conducto-convectifs en régime laminaire. Les équations qui décrivent l'écoulement du fluide et le transfert d'énergie sont discrétisées par la méthode des volumes finis. La première partie du mémoire présente une nouvelle technique d'optimisation et sa validation sur des cas d'études de la littérature (single pipe, bend pipe). Cette technique consiste à définir des fonctions d'interpolation de type sigmoïde et permet d'obtenir une amélioration de l'interface fluide-solide au cours du processus d'optimisation. La seconde partie met en évidence les phénomènes physiques dans le canal asymétriquement chauffé, notamment l'influence de la stratification thermique extérieure et du rayonnement de surface sur les quantités aérauliques et thermiques. Enfin, une nouvelle expression de la puissance mécanique pour contrôler les pertes de charge (malgré l'ajout de matière) dans le canal vertical combinée avec une nouvelle expression de la puissance thermique sont étudiées. Le problème ainsi posé est résolu pour un écoulement en convection naturelle. Pour les cas considérés, chacune des fonctions coût est optimisée sans détériorer l'autre. Nous comparons aussi les valeurs des puissances obtenues par notre algorithme avec celles couramment utilisées dans la littérature et montrons que ces nouvelles fonctionnelles sont performantes.

Ventilation plays a key role in thermal comfort of building's occupants in hot climates by refreshing air surrounding them. Mechanical or natural ventilation must be controlled for two reasons: do not disturb the bulding's occupants and comply with the regulations in force. Discomfort is linked to too high air velocities or turbulent intensity. Designers can use the numerical tools for a finer prediction of airflow. The simulation of configurations at the building scale can be done using averaged Navier-Stokes equations approach in addition to a turbulence model. These simulations are used by researchers as sizing tools or for the optimization of ventilation components. In addition, the shape of the ventilation nozzle can passively contributes to the optimization of some aeraulics phenomena. The improvement of these ventilation components can be achieved by the use of shape optimization methods. Topological optimization by addition of material makes it possible for the optimization of cost functions defined on the fluid or on its boundaries. The main objective of this manuscript is to propose a tool to control airflows in building by the search for optimal shape of ventilation nozzle. This work proposes a contribution to the topological optimization of turbulent flows in buildings. In a first step, topological optimization by adding material is applied to minimize pressure losses in a T-shaped pipe. The developed model is subjected to the hypothesis of the frozen turbulence. In a second step, the complete adjoint model is proposed for the standard turbulence model k-epsilon for the minimization of the total pressure losses on the one hand and the turbulent intensity on the other hand. Finally, these tools are applied to the shape optimization of ventilation nozzle. The results of topological optimization by adding virtual material show good potential for the orientation of the airflows but does not guarantee the control of the air velocities in the room. Moreover, the minimization of turbulent intensity through the complete approach contributed to the reduction of the dissatisfaction rate due to excessive turbulent intensity in the room., La ventilation joue un rôle important dans le confort thermique des occupants d'un bâtiment en climat chaud, en contribuant au rafraîchissement de l'air qui les entoure. Qu'elle soit mécanique ou naturelle, la ventilation doit être maîtrisée pour ne pas gêner l'occupant et respecter des normes ou réglementations en vigueur. Ces gênes sont liées à des vitesses d'air ou à une intensité turbulente trop élevée. Les concepteurs doivent alors faire appel à l'outil numérique pour une prédiction fine des écoulements d'air. La simulation de configurations à l'échelle du bâtiment peut se faire par une approche moyennée des équations de Navier-Stokes en complément d'un modèle de turbulence. Ces simulations sont utilisées par les chercheurs comme des outils de dimensionnement, ou encore, d'optimisation des composants de ventilation. De plus, la forme des bouches de ventilation peut contribuer passivement à l'optimisation de certains phénomènes aérauliques. L'amélioration de ces formes peut ainsi se faire par l'utilisation de méthodes d'optimisation de forme. L'optimisation topologique par ajout de matière permet de trouver des formes pour optimiser des fonctionnelles objectifs définies sur le fluide ou sur ses frontières. C'est sur cette méthode que ces travaux de thèse se concentrent pour proposer un outil de contrôle des écoulements d'air dans le bâtiment par la recherche de formes optimales de bouches de ventilation. Ces travaux de thèse proposent une contribution à l'optimisation topologique d'écoulements turbulents dans le bâtiment. Dans un premier temps, la méthode par ajout de matière est appliquée pour minimiser les pertes de charge dans une conduite d'aération en forme de Té. Le modèle adjoint développé est soumis à l'hypothèse de turbulence gelée. Dans un second temps le modèle adjoint complet est proposé pour le modèle de turbulence standard k-epsilon pour la réduction des pertes de charge d'une part et de l'intensité turbulente d'autre part. Enfin, ces outils sont appliqués à l'optimisation de forme de bouches de ventilation. Les résultats montrent ainsi un bon potentiel de l'optimisation topologique par ajout de matière pour l'orientation des écoulements d'air mais ne garantissent pas la maîtrise des vitesses d'air dans la pièce. De plus, la minimisation de l'intensité turbulente grâce à l'approche complète développée a contribué à la réduction du taux d'insatisfaction lié à une intensité turbulente trop élevée dans la pièce.

This thesis deals with topology optimization of mass and heat transfer in the framework of the vertical asymetrically-heated channel. The incompressible Navier-Stokes equations coupled to the convection-diffusion equation through the Boussinesq approximation are employed and are solved with the finite volume method. We first propose a new interpolation technique for heat transfer optimization and validate it on referenced cases such as the "single pipe" and the "bend pipe". This new technique consists in the introduction of sigmoid interpolation functions to obain a better definition of the interface between fluid and solid domains, during the optimization process. We study then physical phenomenon in the asymmetrically heated channel , in particular the influence of thermal stratification outside the channel and surface radiation on thermal and dynamic quantities. We thus highlight the size variation of reversed flow at the exit of the channel and the plug-effect linked on external thermal stratification. Finally, we propose a new expression of mechanical power in order to control charges losses (despite addition of material) in the vertical channel combined with the expression of thermal power. In all considered cases, our algorithm succeeds to enhance one of the phenomenon modelled by our new cost functions without deteriorating the other one. We also compare the values of standard cost functions from the litterature over iteration of our optimization algorithm and show that our new cost functions are effective., Les présents travaux de thèse envisagent une nouvelle technique d'optimisation au sens topologique dans des géométries de type canal vertical où se réalisent des transferts de chaleur conducto-convectifs en régime laminaire. Les équations qui décrivent l'écoulement du fluide et le transfert d'énergie sont discrétisées par la méthode des volumes finis. La première partie du mémoire présente une nouvelle technique d'optimisation et sa validation sur des cas d'études de la littérature (single pipe, bend pipe). Cette technique consiste à définir des fonctions d'interpolation de type sigmoïde et permet d'obtenir une amélioration de l'interface fluide-solide au cours du processus d'optimisation. La seconde partie met en évidence les phénomènes physiques dans le canal asymétriquement chauffé, notamment l'influence de la stratification thermique extérieure et du rayonnement de surface sur les quantités aérauliques et thermiques. Enfin, une nouvelle expression de la puissance mécanique pour contrôler les pertes de charge (malgré l'ajout de matière) dans le canal vertical combinée avec une nouvelle expression de la puissance thermique sont étudiées. Le problème ainsi posé est résolu pour un écoulement en convection naturelle. Pour les cas considérés, chacune des fonctions coût est optimisée sans détériorer l'autre. Nous comparons aussi les valeurs des puissances obtenues par notre algorithme avec celles couramment utilisées dans la littérature et montrons que ces nouvelles fonctionnelles sont performantes.

The aim of this article is to present a vulgarized introduction to the vegetated complex partitions field, called VCP. To reach this goal, the green roof notions, their uses and implications are defined. The theory is illustrated by a Reunion Island case study, which allows to list several impacts of the green walls utilization., En matière de consommation énergétique mondiale, l'augmentation est indiscutablement la tendance actuelle. Conformément au contexte énergétique international, l'île de La Réunion doit faire face à une demande énergétique croissante. Après analyse de la répartition de ces besoins, la régulation thermique du bâti apparaît être l'un des postes les plus énergivores. Afin de réduire l'importance de ce poste, la solution présentement proposée consiste a végétaliser la structure afin d'en réduire la surchauffe. Le présent article est une introduction vulgarisée au domaine des parois complexes végétalisées (PCV). Afin d'accréditer cette prétention, la notion de toiture végétalisée, leurs utilisations, ainsi que les différentes modifications quelles induisent y sont définies. L'illustration des propos est permise par l'application d'un cas d'étude concret, celui d'une utilisation sur l'île de La Réunion. Cette dernière permettant de définir divers impacts du système dans ces conditions.

Context: Air-conditioning represents a high-energy expenditure in the sector of the building, which could be reduced drastically through the use of passive cooling systems. In hot and humid climates, the passive cooling of premises is a tried and tested technique ordained around four principles: to minimize the external and internal heat transfers, to bring inertness to the building, to humidify the air, and to ensure a good convection in order to favor convective exchanges. Objective: The description of thermo-convective transfers (estimation of mass flows rate and heat transfers) set in open cavities (rooms with crossing ventilation, solar chimney, outer skin of a double facade,...) is still relatively uncommon and the stakes are high to improve passive systems. The study of these phenomena can be evaluated through computational fluid dynamics. This thesis’s objectives are to achieve precise numerical simulations of airflow inspecific configurations of passive systems in damp tropical climates, in order to improve and deepen our knowledge of natural convection and to begin to give information concerning the choice of numerical boundary conditions to apply to open geometries.Numerical approach: The numerical approach adopted in this work, to study the natural turbulent convection, is the Large-Eddy Simulation. This approach is halfway between a direct numerical simulation and Reynolds-averaged Navier–Stokes equations. Such a technique is advantageous as it leads to a necessary substantial reduction of the number of discretizationpoints compared to the technique of direct simulation requirements, while retaining the dynamic aspect of the flows. Results: The results obtained in this work refer to the study of the dynamic boundary conditions to impose in open geometries with SND and to the application of the LES to different configurations of open cavities with a turbulent flow, in order to characterize temperature and velocity fields and then deduce mass flow rate, enthalpy flow,... The results have been compared either to other numerical results in the framework of national benchmarks (benchmark AmeThand ADNBâti) or to experimental results.; Contexte du sujet : La climatisation est un poste de dépense énergétique important dans le secteur du bâtiment, qui pourrait être réduit de manière drastique par l’utilisation de systèmes passifs de rafraîchissement. Dans les climats chauds et humides, le rafraîchissement passif des bâtiments est une solution éprouvée, qui s’ordonne autour de quatre principes : minimiser les apports de chaleur interne et externe, apporter de l’inertie au bâtiment, humidifier l’air et assurer une bonne ventilation pour favoriser les échanges convectifs. Objectifs : La description des transferts thermo-convectifs (évaluation des débits massiques, des transferts de chaleur) mis en jeu dans des cavités ouvertes (pièces avec ventilation traversante, cheminées solaires, doubles peaux, espaces sous-toiture) est encore mal connue et constitue un enjeu pour l’amélioration des systèmes passifs. L’étude de ces phénomènes peut être évaluée par la mécanique des fluides numérique. Les objectifs de ce travail de thèse sont : de réaliser des simulations numériques fines du comportement thermo-aéraulique dans des configurations typiques de systèmes passifs en climat tropical humide, afin d’améliorer nos connaissances sur la ventilation naturelle, d’approfondir et d’apporter des éléments de réponses en ce qui concerne le choix des conditions limites numériques à appliquer pour les systèmes ouverts. Modélisation numérique : L’approche numérique adoptée dans ce travail, pour étudier la convection naturelle turbulente, est la simulation des grandes échelles (SGE ou LES en anglais). Cette approche se situe à mi-parcours entre la méthode de calcul direct et la résolution des équations moyennées en temps, de type RANS. L’avantage d’une telle technique est la réduction appréciable du nombre de points de discrétisation nécessaire par rapport à celui exigé par la méthode de calcul direct, tout en conservant l’aspect dynamique des écoulements. Résultats : Les résultats obtenus lors de ce travail concernent l’étude des conditions limites dynamiques à imposer pour des géométries ouvertes avec une SND et l’application de la SGE à différentes configurations de cavités ouvertes en régime turbulent, afin de caractériser les champs de température et de vitesse et d’en déduire les grandeurs intégrales d’intérêt (débit massique, débit enthalpique, renouvellement d’air,... ). Les résultats de ces calculs ont été comparés soit à d’autres résultats numériques dans le cadre de benchmarks nationaux (benchmark numérique AmeTh et ADNBâti) ou à des résultats expérimentaux.