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En rivière à lit de graviers, le transport des sédiments en charge de fond est un processus intermittent qui dépend de plusieurs variables du système fluvial dont la prédiction est encore aujourd’hui inexacte. Les modèles disponibles pour prédire le transport par charriage utilisent des variables d’écoulement moyen et la turbulence n’est généralement pas considérée malgré que les tourbillons contenus dans les écoulements possèdent une quantité d’énergie importante. L’utilisation de nouvelles approches pour étudier la problématique du transport par charriage pourrait nous permettre d’améliorer notre connaissance de ce processus déterminant en rivière alluviale. Dans ce mémoire, nous documentons ces composantes de la dynamique fluviale dans un cours d’eau graveleux en période de crue. Les objectifs du projet de recherche sont : 1) d’examiner l’effet du débit sur les variables turbulentes et les caractéristiques des structures turbulentes cohérentes, 2) d’investiguer l’effet du débit sur les caractéristiques des événements de transport de sédiments individuels détectés à l’aide d’un nouvel algorithme développé et testé et 3) de relier les caractéristiques de l’écoulement turbulent aux événements de transport de sédiments individuels. Les données de turbulence montrent qu’à haut niveau d’eau, l’écoulement décéléré est peu cohérent et a une turbulence plus isotrope où les structures turbulentes cohérentes sont de courte durée. Ces observations se distinguent de celles faites à faible niveau d’eau, en écoulement accéléré, où la plus grande cohérence de l’écoulement correspond à ce qui est généralement observé dans les écoulements uniformes en rivières graveleuses. Les distributions de fréquence des variables associées aux événements de transport individuel (intensité de transport moyenne, durée d’événement et intervalle entre événements successifs) ont des formes différentes pour chaque intensité de crue. À haut niveau d’eau, le transport est moins intermittent qu’à faible débit où les événements rares caractérisent davantage les distributions. L’accélération de l’écoulement à petite échelle de temps joue un rôle positif sur le transport, mais surtout lorsque la magnitude de la crue mobilisatrice est en dessous du niveau plein bord. Les résultats de l’étude montrent que les caractéristiques de la turbulence ainsi que les liens complexes entre l’écoulement et le transport par charriage sont fonction du débit. / In gravel-bed rivers, bedload transport is an intermittent process related to many variables of the fluvial system whose prediction is still unreliable. Available models for prediction of bedload transport use mean hydraulics variables and generally do not consider turbulence even if coherent turbulent flow structures in rivers are highly energetic. New approaches to bedload transport investigation can shed light on this very important process in alluvial channels. In this thesis, we document these components of the fluvial system in a gravel-bed river during a flood. The objectives of the research are to: 1) investigate the effect of discharge on turbulent variables and turbulent coherent flow structures, 2) investigate the effect of discharge on bedload transport events statistics detected with a newly developed and tested algorithm and 3) link turbulent flow characteristics to individual bedload transport events. Turbulence data shows that at high water level, the decelerated flow has a low coherency and an isotropic turbulence where coherent turbulent flow structures have a short duration. These observations differ from those made at low water level where the accelerated flow corresponds to what is generally observed in uniform flows of gravelly channels. Frequency distributions of bedload transport events variables (mean bedload transport rate, event duration and time interval between successive bedload events) have different shapes for the two investigated flood intensity. At high water level, bedload transport is less intermittent that at low discharge where distributions are more characterised by rare events. Flow velocity acceleration on a short time scale has a positive effect on bedload transport, but mainly when the mobilizing flood is under bankfull stage. Results from the study show that turbulence properties and complex relationships between turbulence and bedload transport are a function of discharge.

Τα ολοκληρωμένα ηλιακά συστήματα συλλέκτη αποθήκης αποτελούνται από μία δεξαμενή αποθήκευσης, της οποίας τμήμα της επιφάνειας της χρησιμοποιείται σαν ηλιακός συλλέκτης. Συνήθως το ρευστό της αποθήκης είναι το νερό χρήσης. Στο υπό εξέταση σύστημα το νερό χρήσης θερμαίνεται έμμεσα, διερχόμενο μέσα από σωληνώσεις εναλλάκτη θερμότητας που τοποθετείται στο εσωτερικό της παραλληλεπίπεδης δεξαμενής. Για την εντατικοποίηση της μετάδοσης θερμότητας προς το νερό χρήσης, δημιουργείται ανάδευση του ρευστού του δοχείου μέσω κυκλοφορητή, ο οποίος τίθεται σε λειτουργία μόνο όταν υπάρχει ζήτηση ζεστού νερού. Προς αποφυγή παραμορφώσεων τοποθετούνται πτερύγια συγκράτησης που ενώνουν τις δύο μεγάλες επιφάνειες της δεξαμενής. Στην παρούσα διδακτορική διατριβή διερευνήθηκαν τα ροϊκά φαινόμενα στο εσωτερικό του ICS που έχει περιγραφεί προηγουμένως, με στόχο τη μεγιστοποίηση της θερμανταλλαγής μεταξύ των δύο κυκλωμάτων νερού. Για την παρατήρηση του ροϊκού πεδίου καθώς και την λήψη μετρήσεων ταχυτήτων κατασκευάστηκε πειραματική συσκευή με διαφανή τοιχώματα από Plexiglas. Ελήφθησαν μετρήσεις ταχυτήτων και διακυμάνσεων με χρήση συστήματος Laser Doppler διπλής ακτίνας. Για την οπτικοποίηση του ροϊκού πεδίου τοποθετήθηκαν σωματίδια πολυστερίνης στο εσωτερικό της συσκευής. Ελήφθησαν ψηφιακές φωτογραφίες και βιντεοσκοπήσεις του ροϊκού πεδίου. Για την υπολογιστική προσομοίωση χρησιμοποιήθηκε το εμπορικό λογισμικό FLUENT. Αναπτύχθηκε υπολογιστικό μοντέλο και επιλύθηκε με όλα τα διαθέσιμα μοντέλα τύρβης. Στη συνέχεια πραγματοποιήθηκε σειρά υπολογιστικών προσομοιώσεων, στις οποίες διερευνήθηκε η βέλτιστη θέση και το μέγεθος των στομίων ανακυκλοφορίας, η βέλτιστη διάταξη των πτερυγίων συγκράτησης και η βέλτιστη θέση του εναλλάκτη. Επιπλέον προσδιορίστηκε υπολογιστικά και πειραματικά ο χρόνος αποκατάστασης του ροϊκού πεδίου. Τέλος, τα αποτελέσματα συγκρίθηκαν και με πειραματικά αποτελέσματα άλλων εργασιών. Τα συμπεράσματα που εξάγονται έχουν ως ακολούθως: Το μοντέλο τύρβης standard k-ω δίνει τα πιο αξιόπιστα αποτελέσματα. Το υπολογιστικό μοντέλο θεωρείται πιστοποιημένο μετά από πειραματική επιβεβαίωση ταχυτήτων και θερμοκρασιών. Το στόμιο ανακυκλοφορίας δεν πρέπει να τοποθετείται κάθετα στις μεγάλες επιφάνειες της δεξαμενής, ενώ η διάμετρος του πρέπει να είναι 1/2" ή και μικρότερη. Ο χρόνος αποκατάστασης του ροϊκού πεδίου είναι περίπου 35 s. Τα πτερύγια συγκράτησης πρέπει να ακολουθούν τις ροικές γραμμές. Ως βέλτιστη θέση του εναλλάκτη θεωρείται όταν τοποθετείται σε επαφή με το τοίχωμα. / Integrated Collector Storage (ICS) solar systems use part of the hot water storage as collector, i.e. half of the storage surface is used as absorber. Usually, the storage medium serves also as the energy transfer medium (service hot water). In the examined ICS, the service water is heated indirectly, passing through a serpentine heat exchanger placed inside the tank. The heat transfer from the stored water to the service water is intensified by the agitation of the stored water. A simple solution is the recirculation of the stored water by a small pump, which is functioning whenever a request for hot water exists. Fins in suitable positions, connect the front and back surface of the ICS, to withstand the deformation due to pressures by the tank water. In the present PhD thesis, the flow phenomena inside the ICS previous mentioned, are investigated. The aim is the maximization of the heat transfer between the two water circuits. An experimental device was constructed by transparent Plexiglas, for flow visualization and velocity measurements. A dual beam Laser Doppler Velocimetry (LDV) system was used to measure velocities. Polystyrene particles were added in the comprised water, for the visualization of the path lines. Photographs and video films were also taken. The commercial code FLUENT is used for the Computational Fluid Dynamics (CFD) simulations. A CFD model is developed and solutions are obtained using all the available turbulence models. Three main factors that influence the performance are optimized: the position and size of the recirculation ports, the arrangement and size of the interconnecting fins and the heat exchanger placement. The settling time, i.e., the time required for the flow field to be fully developed, is computed both numerically and experimentally. The previous analysis leads to the following conclusions: The standard k–ω model is selected as the most appropriate. The model is validated, with good agreement, against experimental measurements of velocities and temperatures. The placement of the inlet recirculation port perpendicular to the main surfaces of the ICS should be avoided, while its diameter should be 1/2" or less. The settling time is computed about 35s. The interconnecting fins, of the two main ICS surfaces should follow the flow filed path lines. The optimal placement of the tube heat exchanger is in contact with the two major surfaces of the storage tank.

En rivière à lit de graviers, le transport des sédiments en charge de fond est un processus intermittent qui dépend de plusieurs variables du système fluvial dont la prédiction est encore aujourd’hui inexacte. Les modèles disponibles pour prédire le transport par charriage utilisent des variables d’écoulement moyen et la turbulence n’est généralement pas considérée malgré que les tourbillons contenus dans les écoulements possèdent une quantité d’énergie importante. L’utilisation de nouvelles approches pour étudier la problématique du transport par charriage pourrait nous permettre d’améliorer notre connaissance de ce processus déterminant en rivière alluviale. Dans ce mémoire, nous documentons ces composantes de la dynamique fluviale dans un cours d’eau graveleux en période de crue. Les objectifs du projet de recherche sont : 1) d’examiner l’effet du débit sur les variables turbulentes et les caractéristiques des structures turbulentes cohérentes, 2) d’investiguer l’effet du débit sur les caractéristiques des événements de transport de sédiments individuels détectés à l’aide d’un nouvel algorithme développé et testé et 3) de relier les caractéristiques de l’écoulement turbulent aux événements de transport de sédiments individuels. Les données de turbulence montrent qu’à haut niveau d’eau, l’écoulement décéléré est peu cohérent et a une turbulence plus isotrope où les structures turbulentes cohérentes sont de courte durée. Ces observations se distinguent de celles faites à faible niveau d’eau, en écoulement accéléré, où la plus grande cohérence de l’écoulement correspond à ce qui est généralement observé dans les écoulements uniformes en rivières graveleuses. Les distributions de fréquence des variables associées aux événements de transport individuel (intensité de transport moyenne, durée d’événement et intervalle entre événements successifs) ont des formes différentes pour chaque intensité de crue. À haut niveau d’eau, le transport est moins intermittent qu’à faible débit où les événements rares caractérisent davantage les distributions. L’accélération de l’écoulement à petite échelle de temps joue un rôle positif sur le transport, mais surtout lorsque la magnitude de la crue mobilisatrice est en dessous du niveau plein bord. Les résultats de l’étude montrent que les caractéristiques de la turbulence ainsi que les liens complexes entre l’écoulement et le transport par charriage sont fonction du débit. / In gravel-bed rivers, bedload transport is an intermittent process related to many variables of the fluvial system whose prediction is still unreliable. Available models for prediction of bedload transport use mean hydraulics variables and generally do not consider turbulence even if coherent turbulent flow structures in rivers are highly energetic. New approaches to bedload transport investigation can shed light on this very important process in alluvial channels. In this thesis, we document these components of the fluvial system in a gravel-bed river during a flood. The objectives of the research are to: 1) investigate the effect of discharge on turbulent variables and turbulent coherent flow structures, 2) investigate the effect of discharge on bedload transport events statistics detected with a newly developed and tested algorithm and 3) link turbulent flow characteristics to individual bedload transport events. Turbulence data shows that at high water level, the decelerated flow has a low coherency and an isotropic turbulence where coherent turbulent flow structures have a short duration. These observations differ from those made at low water level where the accelerated flow corresponds to what is generally observed in uniform flows of gravelly channels. Frequency distributions of bedload transport events variables (mean bedload transport rate, event duration and time interval between successive bedload events) have different shapes for the two investigated flood intensity. At high water level, bedload transport is less intermittent that at low discharge where distributions are more characterised by rare events. Flow velocity acceleration on a short time scale has a positive effect on bedload transport, but mainly when the mobilizing flood is under bankfull stage. Results from the study show that turbulence properties and complex relationships between turbulence and bedload transport are a function of discharge.

Ziel der vorliegenden Arbeit ist es, Rühr- und Mischungsvorgänge in Flüssigmetallströmungen zu untersuchen, die mittels rotierender und wandernder Magnetfelder bzw. deren Kombination induziert werden. Im Mittelpunkt steht dabei die Charakterisierung der dreidimensionalen Strömungsstrukturen innerhalb zylindrischer Geometrien bei der Verwendung überkritischer Magnetfelder. Neben der Untersuchung der Strömungseigenschaften stellen die physikalische Modellierung der angreifenden Kräfte, die geeignete Wahl und Validierung eines effizienten numerischen Lösungsverfahrens und dessen Erweiterung für die Durchführung von Large Eddy Simulationen wesentliche Eckpfeiler dieser Arbeit dar.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Uma simulação numérica que leva em conta os efeitos de estratificação e mistura escalar (como a temperatura, salinidade ou substância solúvel em água) é necessária para estudar e prever os impactos ambientais que um reservatório de usina hidrelétrica pode produzir. Este trabalho sugere uma metodologia para o estudo de escoamentos ambientais, principalmente aqueles em que o conhecimento da interação entre a estratificação e mistura pode dar noções importantes dos fenômenos que ocorrem. Por esta razão, ferramentas de simulação numérica 3D de escoamento ambiental são desenvolvidas. Um gerador de malha de tetraedros do reservatório e o modelo de turbulência algébrico baseado no número de Richardson são as principais ferramentas desenvolvidas. A principal dificuldade na geração de uma malha de tetraedros de um reservatório é a distribuição não uniforme dos pontos relacionada com a relação desproporcional entre as escalas horizontais e verticais do reservatório. Neste tipo de distribuição de pontos, o algoritmo convencional de geração de malha de tetraedros pode tornar-se instável. Por esta razão, um gerador de malha não estruturada de tetraedros é desenvolvido e a metodologia utilizada para obter elementos conformes é descrita. A geração de malha superficial de triângulos utilizando a triangulação Delaunay e a construção do tetraedros a partir da malha triangular são os principais passos para o gerador de malha. A simulação hidrodinâmica com o modelo de turbulência fornece uma ferramenta útil e computacionalmente viável para fins de engenharia. Além disso, o modelo de turbulência baseado no número de Richardson leva em conta os efeitos da interação entre turbulência e estratificação. O modelo algébrico é o mais simples entre os diversos modelos de turbulência. Mas, fornece resultados realistas com o ajuste de uma pequena quantidade de parâmetros. São incorporados os modelos de viscosidade/difusividade turbulenta para escoamento estratificado. Na aproximação das equações médias de Reynolds e transporte de escalar é utilizando o Método dos Elementos Finitos. Os termos convectivos são aproximados utilizando o método semi-Lagrangeano, e a aproximação espacial é baseada no método de Galerkin. Os resultados computacionais são comparados com os resultados disponíveis na literatura. E, finalmente, a simulação de escoamento em um braço de reservatório é apresentada. / To study and forecast the environmental impacts that a hydroelectric power plant reservoir may produce, a numerical simulation that takes into account the effects of stratification and scalar mixing (such as temperature, salinity or water-soluble substance) is required. This work proposes a methodology for the study of the environmental fluid flow phenomena, mainly for flows in which the knowledge of the interaction between stratification and mixing can give important notions of the phenomena that occur. For this, a numerical simulation tool for 3D environmental flow is developed. A tetrahedral mesh generator of the reservoir based on the terrain topology and an algebraic turbulence model based on the Richardson number are the main tools developed. The main difficulty in tetrahedral mesh generation of a reservoir is nonuniform distribution of the points related to the huge ratio between the horizontal and vertical scales of the reservoir. In this type of point distributions, conventional tetrahedron mesh generation algorithm may become unstable. For this reason, a unstructured tetrahedral mesh generator is developed and the methodology used to obtain conforming elements is described. Triangular surface mesh generation using the Delaunay triangulation and the construction of the tetrahedra from the triangular surface mesh are the main steps to the mesh generator. The hydrodynamic simulation of reservoirs with a turbulence model provides a useful tool that is computationally viable for engineering purposes. Furthermore, the turbulence model based on the Richardson number takes into account the effects of interaction between turbulence and stratification. The algebraic model is the simplest among the various models of turbulence, but provides realistic results with the fitting of a small amount of parameters. Eddy-Viscosity/Diffusivity models for stratified turbulent flows models are incorporated. Using the Finite Element Method (FEM) approximation the Reynolds-averaged Navier-Stokes (RANS) and mean scalar transport equations are approximated. The convective terms are discretized employing the Semi-Lagrangian method, and the spatial discretization is based on the Galerkin method. The computational results are compared with the results available in the literature. Finally, the simulation of the flow in a branch of a reservoir is presented.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Uma simulação numérica que leva em conta os efeitos de estratificação e mistura escalar (como a temperatura, salinidade ou substância solúvel em água) é necessária para estudar e prever os impactos ambientais que um reservatório de usina hidrelétrica pode produzir. Este trabalho sugere uma metodologia para o estudo de escoamentos ambientais, principalmente aqueles em que o conhecimento da interação entre a estratificação e mistura pode dar noções importantes dos fenômenos que ocorrem. Por esta razão, ferramentas de simulação numérica 3D de escoamento ambiental são desenvolvidas. Um gerador de malha de tetraedros do reservatório e o modelo de turbulência algébrico baseado no número de Richardson são as principais ferramentas desenvolvidas. A principal dificuldade na geração de uma malha de tetraedros de um reservatório é a distribuição não uniforme dos pontos relacionada com a relação desproporcional entre as escalas horizontais e verticais do reservatório. Neste tipo de distribuição de pontos, o algoritmo convencional de geração de malha de tetraedros pode tornar-se instável. Por esta razão, um gerador de malha não estruturada de tetraedros é desenvolvido e a metodologia utilizada para obter elementos conformes é descrita. A geração de malha superficial de triângulos utilizando a triangulação Delaunay e a construção do tetraedros a partir da malha triangular são os principais passos para o gerador de malha. A simulação hidrodinâmica com o modelo de turbulência fornece uma ferramenta útil e computacionalmente viável para fins de engenharia. Além disso, o modelo de turbulência baseado no número de Richardson leva em conta os efeitos da interação entre turbulência e estratificação. O modelo algébrico é o mais simples entre os diversos modelos de turbulência. Mas, fornece resultados realistas com o ajuste de uma pequena quantidade de parâmetros. São incorporados os modelos de viscosidade/difusividade turbulenta para escoamento estratificado. Na aproximação das equações médias de Reynolds e transporte de escalar é utilizando o Método dos Elementos Finitos. Os termos convectivos são aproximados utilizando o método semi-Lagrangeano, e a aproximação espacial é baseada no método de Galerkin. Os resultados computacionais são comparados com os resultados disponíveis na literatura. E, finalmente, a simulação de escoamento em um braço de reservatório é apresentada. / To study and forecast the environmental impacts that a hydroelectric power plant reservoir may produce, a numerical simulation that takes into account the effects of stratification and scalar mixing (such as temperature, salinity or water-soluble substance) is required. This work proposes a methodology for the study of the environmental fluid flow phenomena, mainly for flows in which the knowledge of the interaction between stratification and mixing can give important notions of the phenomena that occur. For this, a numerical simulation tool for 3D environmental flow is developed. A tetrahedral mesh generator of the reservoir based on the terrain topology and an algebraic turbulence model based on the Richardson number are the main tools developed. The main difficulty in tetrahedral mesh generation of a reservoir is nonuniform distribution of the points related to the huge ratio between the horizontal and vertical scales of the reservoir. In this type of point distributions, conventional tetrahedron mesh generation algorithm may become unstable. For this reason, a unstructured tetrahedral mesh generator is developed and the methodology used to obtain conforming elements is described. Triangular surface mesh generation using the Delaunay triangulation and the construction of the tetrahedra from the triangular surface mesh are the main steps to the mesh generator. The hydrodynamic simulation of reservoirs with a turbulence model provides a useful tool that is computationally viable for engineering purposes. Furthermore, the turbulence model based on the Richardson number takes into account the effects of interaction between turbulence and stratification. The algebraic model is the simplest among the various models of turbulence, but provides realistic results with the fitting of a small amount of parameters. Eddy-Viscosity/Diffusivity models for stratified turbulent flows models are incorporated. Using the Finite Element Method (FEM) approximation the Reynolds-averaged Navier-Stokes (RANS) and mean scalar transport equations are approximated. The convective terms are discretized employing the Semi-Lagrangian method, and the spatial discretization is based on the Galerkin method. The computational results are compared with the results available in the literature. Finally, the simulation of the flow in a branch of a reservoir is presented.

Les transferts de chaleur par convection forcée turbulente dans une conduite plane partiellement remplie par un milieu poreux sont étudiés numériquement. L’étude concerne l’analyse de l’encrassement dans un canal plan représentatif d’un échangeur de chaleur à plaques. Un fluide, ayant un fort pouvoir encrassant, est considéré en régime turbulent. L’objectif de cette étude est de proposer une technique qui repose sur l’utilisation de matériaux fibreux comme capteur de particules pouvant réduire les méfaits de l’encrassement. Cela consiste à essayer de réduire la résistance d’encrassement en agissant sur les propriétés thermiques du dépôt. L’étude de la cinétique de l’encrassement permet de déterminer la loi de variation de l’épaisseur du dépôt au cours du temps. Cette équation est couplée aux équations de conservation. Un modèle de conductivité thermique effective (fluide, dépôt, fibres poreuses) a été choisi et le phénomène de colmatage de la matrice poreuse est considéré. L’apport du milieu poreux sur les performances de l’échangeur est analysé / A numerical study is carried out to investigate the forced convection heat transfer induced by a turbulent flow in a parallel plate channel partly filled with a porous or fibrous material. The study involves the analysis of fouling in a plate heat exchanger, represented by a parallel plate channel with a high fouling potential liquid flow in turbulent regime. The objective is to come out with a technical solution that relies on the use of fibrous materials capability to capture deposited particles, and therefore to reduce the fouling impacts within heat exchangers. This solution focuses on reducing the fouling resistance on wall surfaces by modifying the thermal properties of the deposit. The deposit thickness evolution is obtained through a kinetics model of fouling, which is coupled to the conservation equations. An effective thermal conduction model (liquid, deposit, porous material) is selected in order to account for fouling within the porous matrix. The benefits of porous material on heat exchanger performance are analyzed

De récentes études expérimentales ont montré que les valeurs usuelles du coefficient d’échange convectif sont différentes en présence de matériaux à changement de phase. Cette thèse de doctorat porte sur l'étude numérique des échanges convectifs fluide/paroi dans une cavité ouverte en régime dynamique. Plus précisément, les parois étudiées sont une paroi avec une capacité thermique et une paroi qui contient des matériaux à changement de phase. Trois modèles distincts ont été développés. Dans un premier temps un modèle (modèle 1) qui concerne l’interaction fluide-paroi à la surface d’une paroi résistive (temperature imposée) en régime laminaire stationnaire a été développé et validé. Les résultats ont été confrontés avec la littérature. Ensuite, les échanges convectifs à la surface d’une plaque capacitive (modèle 2) soumise à une rampe de température d’air ont été étudiés. Finalement, un troisième modèle (modèle 3) a été développé, à la suite du modèle 2. Ce dernier modèle concerne l’interaction fluide-paroi à la surface d’une paroi contenant des matériaux à changement de phase en régime dynamique. Les résultats obtenus révèlent des pics locaux du flux de chaleur au cours du temps. Ce fait témoigne du changement d’état à l’intérieur de la paroi qui contient le materiau à changement de phase. De plus, les courbes des coefficients d’échanges convectifs moyens révèlent la dépendance du coefficient d’echange convectif à la capacité thermique du materiau. Par conséquent, la présence des matériaux à changement de phase à l’intérieur d'une paroi influence l’évolution et la forme de la couche limite thermique. / Recent experimental studies have shown that the usual values ​​of the convective heat transfer coefficient h are no longer valid in the presence of phase change materials. Three separate models were developed. Initially a model 1 which treats the fluid-wall (constant temperature) interaction in steady laminar flow has been developed and validated. Then, the wall with heat capacity (model 2) subjected to an air temperature ramp were studied. Finally, a third model (3) has been developed which treats the interaction fluid-wall which contains a phase change material. The results show local peaks of heat flow over time. This fact reflects the phase change inside the wall. Moreover, the curves of the convective heat transfer coefficient indicate the dependence of the coefficient h to the wall’s energy storage capacity. Therefore, the presence of the phase change materials within a wall effect and changes the shape of the thermal boundary layer.

Diploma thesis is focused on modeling rotor downwash generated by the main rotor of helicopter and analyzing its effects on the roof structure. Theoretical definition of rotor downwash flow is described in the first part of the text. Governing equations of computational fluid dynamics are briefly explained as well as boundary layer and finite volume method. Next part inquires into numerical simulation of rotor downwash based on height of rotor above the roof, shape of roof plane and climatic conditions. Results are compared with climatic load values provided by actual Czech construction standard in the end of the text.