In this research, hydrodynamic analysis, verification and validation will be performed on Generic Prismatic Planing Hull (GPPH) using OpenFOAM v1806 solver interFoam. The numerical simulation will be compared with the experimental result, which is a new set of high-quality experimental tests performed on a large model of a high deadrise prismatic planing hull with flat of chine, tested from pre-planing to fully planing regimes. Firstly, the mesh convergence study and Verification and Validation (V&V) study are performed on the basis of fixed attitude simulations. Three grids are chosen and used to perform the free attitude simulations at the highest speed. Then, mesh convergence study is conducted for the results of highest speed free body simulations, which helps us to choose two grids for other speeds simulations. By performing free attitude simulations using two grids, resistance, heave, trim angle, wetted chine length, and wetted keel length are calculated and compared at seven different tested speeds. Computational Fluid Dynamics (CFD) results analysis regards pressure distribution on the bottom of the hull and in particular areas of interest (flat of chine, spray area, etc.), friction coefficient and volume fraction of fluid in areas where the free surface undergoes violent deformations (overturning wave at the chine and in the wake, spray jet development area). Different algorithms for dynamic mesh simulation and their effect on the quality of CFD predictions are also investigated. / Master of Science / The paper presents the first series of results obtained in an ongoing validation and verification study of inter-dynamic OpenFOAM solver framework on a new set of high quality experimental tests performed on a large (2.4m long) generic planing hull model (GPPH) with high deadrise (18deg), from the pre-planning (Fn∇=2.6) to fully planing (Fn∇=5.7) regimes. This test case is a good benchmark for the free surface capturing model implemented in OpenFOAM which is based on a rather simple transport equation for an additional scalar field that defines the fraction of water in each cell of the computational mesh. This model, in spite of its simplicity, seems capable of reproducing complex violent free surface flows such as that observed in planing hulls, that includes jet spray forming on the bottom and detaching from the chine of the planing hull and overturning waves off the wet chine region, with some nuances. The dependence of the flow solution on the mesh quality is presented and discussed. Practical indication of the level of uncertainty of CFD models for the prediction of the calm water hydrodynamics of the GPPH is given at the highest simulated speed using both fixed and free attitude simulation solutions. Predictions are then extended to the whole speed range, including resistance components, dynamic trim, heave, wetted chine length, and wetted keel length.The effect due to algorithms is also discussed by modifying the settings in wall functions and solvers for the improvements of future simulation.

A new state-of-the-art CFD solver capable of simulating a broad range of complex engineering flows at real-life Reynolds numbers is developed. The method solves the three-dimensional incompressible unsteady Reynolds-averaged Navier-Stokes (URANS) equations closed with statistical turbulence models. Three such models are incorporated in the solver: the standard k - e model with wall functions, the Spalart-Allmaras model and the detached-eddy simulation (DES) model. The numerical solver employs domain decomposition with structured Chimera overset grids to handle complex, multi-connected geometries. The governing equations are discretized with second order accuracy schemes both in space and time. The capabilities and versatility of the numerical method are demonstrated by applying it to simulate two widely different flow problems: a) flow past a geometrical complex array of multiple bridge piers mounted both on a natural river reach and on a flat bed experimental flume; and b) flow in mechanical, bileaflet, prosthetic heart valve with the leaflets fixed in the fully-open position. Overset grid systems with several millions of grid nodes are used and grid-refinement and other numerical dependency studies are carried out to explore the sensitivity of the computed solutions to various numerical parameters. For all simulated cases, large-scale unsteadiness appears naturally as a result of excited mean-flow instabilities and the computed mean flowfields are shown to be in good quantitative agreement with experimental measurements. By analyzing the instantaneous flowfields numerous novel insights into the physics of both flow cases are obtained and discussed extensively. The results of this thesis demonstrate the potential of the new method as a powerful simulation tool for a broad range of cross-disciplinary engineering flow problems and underscore the need for physics-based numerical modeling by integrating CFD with laboratory experimentation.

The use of Large Eddy Simulation (LES) for modelling air flows in buildings is a growing area of Computational Fluid Dynamics (CFD). Compared to traditional CFD techniques, LES provides a more detailed approach to modelling turbulence in air. This offers the potential for more accurate modelling of low energy natural ventilation which is notoriously difficult to model using traditional CFD. Currently, very little is known about the performance of LES for modelling natural ventilation, and its computational intensity makes its practical use on desk top computers prohibitive. The objective of this work was to apply LES to a variety of natural ventilation strategies and to compile guidelines for practitioners on its performance, including the trade-off between accuracy and cost.

Les barrages sur les rivières sont des obstacles à la migration piscicole. Les passes à poissons sont des ouvrages permettant aux espèces piscicoles de migrer, autorisant le rétablissement de la continuité écologique des cours d'eau. Le but de ce travail est de mieux comprendre les phénomènes physiques présents dans les passes à poissons naturelles. Ces passes sont des canaux à forte pente, équipé de rangées de plots en quinconce. Pour valider la pertinence de l'utilisation d'un modèle numérique, l'étude s'est limitée à l'écoulement autour d'un cylindre émergent placé au centre d'un canal. Le travail est décomposé en deux parties, une expérimentale et une numérique. La partie expérimentale est conduite dans un canal transparent de 4m de long, 0,4m de large et 0,4m de hauteur. Le diamètre du cylindre est 4cm et sa hauteur 20cm (toujours émergent). Les cas étudiés sont des débits de 5, 10, 15 et 20 l/s pour une pente nulle. Les nombres de Froude sont supérieurs à 0,5 et les nombres de Reynolds, basés sur le diamètre, sont compris entre 15000 et 50000. Les écoulements ont été filmés et un algorithme de suivi de particules (PTV) a été développé. Des zones de faibles vitesses existent, même pour Fr=1, pouvant assurer des zones de refuge pour le poisson. Les forces de trainée ont été mesurées sur le plot. Les évolutions des coefficients de trainée avec le nombre de Froude et des rapports de forme de l'écoulement autour du plot ont ainsi été évaluées. La partie numérique est réalisée avec OpenFOAM pour 4 cas d'étude (Q=10 et 20 l/s, S=0 et 2%) et 2 modèles de turbulence URANS, le RNG k-epsilon et le k-omega SST. Des modélisations en 2D ont également été faites avec Telemac 2D. Les résultats obtenus ont été comparés aux résultats expérimentaux. La modélisation 2D (shallow water) est exploitable seulement pour des nombres de Froude faibles, d'où la nécessité des modélisations en 3D. Le modèle komega SST semble le mieux adapté pour reproduire les écoulements étudiés. Les vitesses locales et les structures en 3D, non quantifiables expérimentalement, ont ensuite été décrites. Les influences du fond et de la surface libre sur le sillage apparaissent clairement en provoquant des vitesses verticales et des tourbillons à grandes échelles. Enfin, une simulation en LES a été conduite. Les structures tourbillonnaires sont mieux représentées que pour les modèles URANS, mais les temps de calcul sont grands.

This thesis provides an assessment of various computational strategies for modelling the turbulent flow and heat transfer around in-line tube banks. The research has direct application to the heat exchanger of an Advanced Gas-cooled Reactor (AGR). The suitability and accuracy of different Computational Fluid Dynamic (CFD) techniques were investigated first on generic square in-line tube banks where experimental data are available. The assumption of flow periodicity in all three Cartesian directions is initially investigated whereby the domain size was varied. Wall-resolved Large Eddy Simulations (LES) predict an increasing flow asymmetry with decreasing tube spacing. Two dimensional (2D) and three dimensional (3D) Unsteady Reynolds Averaged Navier-Stokes (URANS) models were simulated at the tube spacing known to be close to the flow pattern transition from symmetric to asymmetric. Marked differences were observed between the flow pattern predicted by turbulence models resolving the boundary layer and those that rely on wall functions. Ultimately, an improved understanding of the flow physics and heat transfer mechanisms encountered within in-line tube banks was gained. The assumption of flow periodicity was then removed and the effects of confining walls were investigated by reproducing experimental conditions. The correct pressure forces and heat transfer around the central tubes could only be accurately predicted when the walls in the crossflow direction were modelled. The inclusion of walls in the spanwise direction gave rise to small flow asymmetries which have been reported on similarly-spaced in-line tube banks. The latter half of the thesis focuses on the reasons for the enhanced thermal mixing and 3D secondary flow patterns observed in the in-line section of the AGR heat exchanger. A wall-resolved periodic LES was conducted at the lower Reynolds number of 11,000 along with URANS calculations of the full experimental conditions at both Reynolds numbers 11,000 and 66,000. These calculations required the use of High Performance Computing (HPC) facilities. Large 3D secondary flow structures were predicted that produced the same level of crossflow temperature drifting as that reported experimentally. Multiple upward and downward flow paths were observed which qualitatively explained why the experimental temperature profiles reported at different spanwise locations indicated multiple spirals (or secondary vortices). Quantification of the levels of thermal diffusion were investigated using both decaying temperature spikes and blanked tube platens. Thus the CFD provided recommendations about the thermal diffusivity assumptions used by the AGR heat exchanger code.

In the present thesis turbulent natural convection of air within different challenging test cases are investigated numerically by means of an unstructured finite volume code, Code_Saturne. First, flow within both two-dimensional vertical and inclined differentially heated rectangular cavities at 60° and 15° to the horizontal for an aspect ratio of H/L=28.6 and Rayleigh number of 0.86×10e6 is computed using several high and low-Re models. Here the effectiveness of the RANS models in Code_Saturne is assessed through comparisons with a range of available experimental data. After some tests of thermal field inside vertical cavity, the “two-velocity-scale wall function” is chosen to be used with high-Re models. In both vertical and inclined cases the overall flow pattern appears similar, with a single circulation cell, and a boundary layer at the wall. The levels of turbulence energy are generally slightly lower in the inclined case. Most models give a reasonable prediction of measured Nusselt number, with the two low-Re approaches generally being closer to the data than the schemes employing wall functions. For the 15° inclined cavity, a multi cellular motion is shown by the high-Re models. Nevertheless, all the model predictions disagree with experimental data due to the presence in real flow of 3-D unsteady structures as found in Benard convection problems. These cannot, definitely, be reproduced using a 2-D geometry. Both highly resolved LES and unsteady RANS computations are then conducted, for turbulent natural convection of air inside 15° unstably and stably stratified cavities. In accordance with recent experimental data, the LES computations for both enclosures returned three-dimensional time-averaged flow fields. In the case of the unstably stratified enclosure, the flow is highly unsteady with coherent turbulent structures in the core of the enclosure. Results of LES computations show close agreement with the measured data. Subsequent comparisons of different URANS schemes with the present LES are used in order to explore to what extent these models are able to reproduce the large-scale unsteady flow structures. All URANS schemes have been found to be able to reproduce the 3-D unsteady flow features present in the 15° unstable cavity. However, the low-Re model tested as well as requiring a high resolution near-wall grid, also needed a finer grid in the core region than the high-Re models, thus making it computationally very expensive. Flow within the 15° stable cavity also shows some 3-D features, although it is significantly less unsteady, and the URANS models tested here have been less successful in reproducing this flow pattern. Finally, natural convection of CO2 inside a horizontal annular penetration enclosure, which can be found in AGR's, has been performed using a highly resolved LES and a set of RANS models. The Rayleigh number is 1.5×10e9. RANS models agree with the present LES on the fact that the flow is unsteady and there are large-scale oscillations present which decrease in amplitude as one moves from the open towards the closed end of the annular enclosure. Overall heat transfer and thermal quantitative and dynamic results show that RANS schemes are in close agreement with the current LES data except some discrepancies shown by the high-Re model which can be returned to the limitation of the simple wall function used to predict such complex flow.

Characterization of distortion transfer and generation through fans with distorted inlet conditions enables progress towards designs with improved distortion tolerance. The abruptness of transition from undistorted to distorted total pressure regions at the inlet impacts the induced swirl profile and therefore the distortion transfer and generation. These impacts are characterized using URANS simulations of PBS Rotor 4 geometry under a variety of inlet distortion profiles. A 90° and a 135° sector, both of 15% total pressure distortion, are considered. Variants of each sector size, with decreasing levels of distortion transition abruptness, are each applied to the fan. Fourier-based distortion descriptors are used to quantify levels of distortion transfer and generation at axial locations through the fan, principally at the stator inlet. It is shown that a gradual transition in distortion at the inlet results in decreased levels of distortion transfer and generation. The flow physics resulting in this reduction are explored. URANS simulations involving turbomachinery are complex and often require simplifying assumptions to balance computational costs with accuracy. One assumption removes the need for a nozzle to control nozzle operation condition and replaces it with a static pressure boundary condition located at the stator exit. This assumption is challenged by conducting a series of distorted inlet simulations with a nozzle, which are then compared to a corresponding set of simulations conducted using the exit boundary assumption. Performance parameters for each set of simulations are compared. Performance was observed to be within 1% difference between the two methods, supporting the assumption that a static pressure boundary is adequate for controlling inlet distortion simulations. Finally, full annulus URANS simulations are presented to investigate distortion phase shift in a single stage transonic fan. The fan is subject to a 90° sector inlet total pressure distortion. Simulation results are presented for choke, design, and near-stall operating conditions. Circumferential profiles of swirl, total pressure, total temperature, power, and phase shift are analyzed at 10%, 30%, 50%, 70%, and 90% span. Several metrics for phase shift, which is a measure of the rotational translation of a distortion profile, are presented and compared. Each aims to assist understanding the translational motion of distortion as it passes through the fan. The different metrics used for phase shift are used to analyze distortion phase. Insights from each are presented alongside limitations for each method. A combination of methods is proposed to address their respective limitations.

An increased understanding of how inlet flow distortion affects transonic fans enables improved fan design and performance prediction. Inlet distortion refers to non-uniformities in the incoming flow properties. Complex inlet ducts in high performance aircraft result in distorted flow at the fan inlet. In this thesis, two studies were performed using Unsteady Reynolds-Averaged Navier Stokes (URANS) simulations. The first study focused on understanding how the transition abruptness between the clean and distorted sector in the inlet Pt profile as well as the circumferential extent of the distorted sector affect distortion transfer and generation through a transonic fan. Simulations on two main distortion sector sizes were carried out. For each sector size, variants with decreasing levels of transition abruptness were applied to the inlet of fan. Simulations were conducted at various operating points, ranging from choke to near-stall. Fourier-based distortion descriptors were used to quantify levels of distortion transfer and generation at various axial locations. It is shown that variations in rotor incidence occur as a result of the applied Pt distortion at the inlet. A less abrupt transition diminishes the local extrema in rotor incidence, which in turn reduces the amount of distortion transfer and generation through the rotor. The near-stall condition is affected most of all operating points considered, with a 23.4% average reduction in the amount of distortion transfer at any span. The size the inlet distorted sector affects the amount of distortion transfer and generation, particularly at the near-stall operating point. This is shown to be due to the dynamic response of the fan. The second study compared the mechanisms of stall inception for cases of both clean and distorted inlet flow. In each instance, the mechanism of stall inception is shown to be interactions between the detached bow shock and the tip clearance vortex. These interactions result in the formation of two vortices within the blade passage. The location and strength of these vortices affect the LE spillage in the adjacent blade rows. Stall inception occurs when the bow shock has moved far enough upstream to allow the resultant vortices from shock/tip clearance vortex interaction to pass in front of the leading edge. When inlet distortion is present, mass redistribution upstream of the fan results in variations in rotor incidence. Within the high incidence region, the bow shock is detached 3.9%-8.1% chord more than the clean inlet case, making LE spillage more severe. The rotating stall cell grows out of the stalled passages present at the near-stall operating point and ultimately extends 180° circumferentially and 18.7% span radially. Understanding the effects of distortion on the mechanisms of stall inception will allow appropriate steps to be taken to extend the stable operating range of modern commercial and high performance fans.

Dans le cadre de la production d'électricité par énergie renouvelable, cette thèse a pour objectif de contribuer à l'amélioration des performances hydrodynamiques des hydroliennes à flux transverse conçues par HydroQuest. Pour y parvenir, deux axes d'étude principaux sont proposés. Le premier consiste à améliorer la compréhension de la performance de l'hydrolienne et de l'écoulement en son sein par voie numérique. L'influence du paramètre d'avance ainsi que celle de la solidité de l'hydrolienne sont étudiées. Les écoulements mis en jeux étant complexes, une méthode de type Simulation des Granges Échelles 3D est utilisée afin de les restituer au mieux. Le phénomène de décrochage dynamique, qui apparaît pour certains régimes de fonctionnement de l'hydrolienne, fait l'objet d'une étude à part entière sur un cas de profil oscillant.Le second axe se concentre sur les carénages de l’hydrolienne qui font l'objet d'une procédure d'optimisation numérique. Afin de pouvoir réaliser les nombreuses simulations requises en un temps réaliste, des méthodes de type Unsteady Reynolds-Averaged Navier-Stokes 2D moins coûteuses et fournissant une précision suffisante pour ce type d'étude sont utilisées. / Within the renewable electricity production framework, this study aims to contribute to the efficiency improvement of the Vertical Axis Hydrokinetic Turbines designed by HydroQuest. To achieve this objective, two approaches are used. The first consists in the improvement of the comprehension of the turbine efficiency such as the flow through the turbine by numerical means. The influence of the tip speed ratio such as the turbine soldity are investigated. The flow through the turbine is complex. A 3D Large Eddy Simulation type is thus used. The dynamic stall phenomenon which could occur in Vertical Axis Hydrokinetic Turbines is also studied in a oscillating blade configuration.The second approach consists in the numerical optimization of the turbine channeling device. To perform the high number of simulations required, a 2D Unsteady Reynolds-Averaged Navier-Stokes simulation type is used.

Les barrages sur les rivières sont des obstacles à la migration piscicole. Les passes à poissons sont des ouvrages permettant aux espèces piscicoles de migrer, autorisant le rétablissement de la continuité écologique des cours d'eau. Le but de ce travail est de mieux comprendre les phénomènes physiques présents dans les passes à poissons naturelles. Ces passes sont des canaux à forte pente, équipé de rangées de plots en quinconce. Pour valider la pertinence de l'utilisation d'un modèle numérique, l'étude s'est limitée à l'écoulement autour d'un cylindre émergent placé au centre d'un canal. Le travail est décomposé en deux parties, une expérimentale et une numérique. La partie expérimentale est conduite dans un canal transparent de 4m de long, 0,4m de large et 0,4m de hauteur. Le diamètre du cylindre est 4cm et sa hauteur 20cm (toujours émergent). Les cas étudiés sont des débits de 5, 10, 15 et 20 l/s pour une pente nulle. Les nombres de Froude sont supérieurs à 0,5 et les nombres de Reynolds, basés sur le diamètre, sont compris entre 15000 et 50000. Les écoulements ont été filmés et un algorithme de suivi de particules (PTV) a été développé. Des zones de faibles vitesses existent, même pour Fr=1, pouvant assurer des zones de refuge pour le poisson. Les forces de trainée ont été mesurées sur le plot. Les évolutions des coefficients de trainée avec le nombre de Froude et des rapports de forme de l'écoulement autour du plot ont ainsi été évaluées. La partie numérique est réalisée avec OpenFOAM pour 4 cas d'étude (Q=10 et 20 l/s, S=0 et 2%) et 2 modèles de turbulence URANS, le RNG k-epsilon et le k-omega SST. Des modélisations en 2D ont également été faites avec Telemac 2D. Les résultats obtenus ont été comparés aux résultats expérimentaux. La modélisation 2D (shallow water) est exploitable seulement pour des nombres de Froude faibles, d'où la nécessité des modélisations en 3D. Le modèle komega SST semble le mieux adapté pour reproduire les écoulements étudiés. Les vitesses locales et les structures en 3D, non quantifiables expérimentalement, ont ensuite été décrites. Les influences du fond et de la surface libre sur le sillage apparaissent clairement en provoquant des vitesses verticales et des tourbillons à grandes échelles. Enfin, une simulation en LES a été conduite. Les structures tourbillonnaires sont mieux représentées que pour les modèles URANS, mais les temps de calcul sont grands. / The dams on rivers are fishes migration obstacles. The fishways are devices allowing the fishes to migrate, permitting the restauration of the ecological continuity. The aim of this work is to better comprehend the physical phenomena existing in the nature-like fishways. This kind of fishway is a high slope channel with staggered rows of blocks. To validate the relevance of the use of a numerical model, the study is limited to the flow around a single free surface piercing cylinder placed in the center of a flume. The work is in two parts, experimental and numérical. The experimental part is conducted in a transparent flume of 4m length, 0.4m width and 0.4m height. The cylinder diameter is 4cm and its height 20cm (always emerged). The studied cases are flow rates of 5 to 20 l/s for a flat bed. The Froude numbers are over 0.5 et the Reynolds numbers, based on the diameter, are in between 15000 and 50000. The flows were filmed and a particules tracking velocimetry (PTV) algorithm was developped. Slow velocities areas exist, even for Fr=1, allowing shelter zones for a fish. The drag forces were also measured. The drag coefficients evolutions with the Froude number and with the flow aspect ratio were estimated. The numerical part is done with OpenFOAM for 4 cases (Q=10 et 20 l/s, S=0 et 2%) and 2 URANS turbulence models, RNG k-epsilon and k-omega SST. 2D simulations are also carried out with Telemac2D. The results are compared with the experimental ones. The 2D modelisation (shallow water) is workable only for small Froude numbers, which justifies the 3D modelisation. The k-omega SST seems the most relevant to reproduce the studied flows. The local velocities and 3D structures, unquantifiable experimentally, were described. The bed and free surface influences on the wake are clearly shown leading to vertical velocities and big scale vorticies. Finally, a LES simulation was conducted. The vortex structures are better reproducted than the URANS simulations, but the computation times are significant.