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This work presents advances towards a linear surface-based model for the jet noise source in simple and complex jets of relevance to the propulsion of high-speed aircraft. The model would be informed by low-cost, Reynolds-Averaged Navier-Stokes (RANS) computations of the flow field. It would be a practical alternative to experiments or high-fidelity computations, such as large eddy simulations (LES), both of which are resource-intensive and entail long turnaround times.This study encompasses one single-stream and two triple-stream jets. The connection between the vortical field and its pressure signature on the edge of the jet is investigated. These regions are represented by the surface of peak Reynolds stress (OSPS) and the “radiator surface” respectively. The radiator surface is the location where the jet noise source model would be prescribed for the computation of its noise propagation.The single-stream jet is an isothermal round jet at Mach 0.9 calculated by large eddy simulation (LES), which enables the computation of two-point space-time correlations throughout the jet and its near-acoustic field. It is observed that the nature of the space-time correlations is different for axial velocity fluctuations and pressure fluctuations. Velocity-based correlations appear to capture localized turbulent events, whereas pressure-based correlations appear dominated by the interaction of large eddies with the surrounding potential flow.Of the triple-stream jets, one is coaxial and the other has an eccentric tertiary flow that yields nose suppression in preferred directions. They are computed by LES and RANS and used to verify key modeling assumptions. In particular, the analysis of velocity scales obtained by two-point correlations validates the RANS-based models for the convective velocity Uc of the noise-generating turbulence, which is a crucial factor in noise generation.The radiator surface is located near the boundary between the rotational and irrotational fields and is defined as the surface on which the Uc distribution equals that on the OSPS. The edge of mean vorticity is nearly coincident with the radiator surface, which suggests a straightforward RANS-based criterion for locating this surface. Additionally, it is found that the edge of the jet is affected by sparse vortices that peel off from the main flow and travel along the radiator surface. Those vortices represent the last remnants of the vortical field and cause a layer of negative pressure skewness at the edge of the jet.Axial and azimuthal turbulence scales are examined on the OSPS and the radiator surface of the three jets, and compared with scales extracted from RANS. Simple relationships are inferred that may aid the development of rapid predictive models.

Since slender bodies have low drag coefficients, they are widely used in naval applications. As they move in the ocean, submersibles leave a trail of turbulence and waves that can persist for a long time in the water. Studying these wakes is challenging as it entails resolving a high-speed flow past a long body, and measuring weak fluctuations in large domains during prolonged times. This thesis is devoted to the computational study of these slender-body wakes. The slender-body wake is thin, slowly-developing and, at high Reynolds numbers, does not exhibit strong vortex shedding. In this work, these particularities are shown to affect the decay of the far wake and the results call into question the notion of universality -- the idea that, far from the body, the turbulent flow `forgets' its initial conditions. In a stratified environment like the ocean, buoyancy effects play a fundamental role in the wake evolution. Buoyancy enhances the mean lifetime of the wake, enables the radiation of internal gravity waves, and triggers the appearance of coherent structures. Understanding these processes is relevant not only to naval applications but also to other problems like the influence of topography in climate models and the navigation of sea animals. Here, highly resolved large-eddy simulations are used to study neutral and stratified slender-body wakes. First, the influence of stratification in the near wake of a prolate spheroid is described. Particular attention is given to the generation of lee waves and the role they play in flow separation. Then, a hybrid method that combines a body-inclusive and a body-exclusive simulation is adopted to enable the first high-Reynolds slender-body far wake study. Contrary to what previous experiments had suggested, the flow in a neutral environment does not conform with classical theory and the dominance of a large-scale helical structure alters the scaling of turbulent dissipation. Finally, comparison with a bluff-body wake reveals that the onset of buoyancy effects depends strongly on the features of the wake generator. This suggests that a parametrization based on local non-dimensional numbers might be necessary to predict the transition between different stratified wake regimes.

Microscale atmospheric simulations of the planetary boundary layer are frequently used for wind energy forecasting, emergency response, mountain meteorology, air pollution modeling, and numerous other applications involving atmospheric flows over complex terrain. These models are typically configured using local observations and are limited to resolving only microscale flow features. Mesoscale meteorology, regional influences, and large-scale turbulence are not resolved with the traditional microscale modeling techniques. This dissertation details a series of developments to the Weather Research and Forecasting (WRF) model that enable mesoscale to microscale (i.e. multiscale) simulations. These multiscale simulations dynamically downscale meteorological conditions through a series of nested domains with increasingly high resolution, which allows mesoscale meteorology, regional influence, and large-scale flow features to influence microscale simulations.Over steep terrain, the WRF model develops numerical errors that are due to grid deformation of the terrain-following coordinates. An alternative gridding technique, the immersed boundary method (IBM), has been implemented into the WRF model (Lundquist et al. 2012; Bao et al. 2018). Use of an IBM allows for microscale simulations over highly complex terrain (i.e. urban or mountainous). Here, an IBM and the WRF model’s grid-nesting framework have been modified to seamlessly work together, which allows for a microscale large-eddy simulation over complex terrain with an IBM to be nested within a traditional mesoscale WRF simulation (Wiersema et al. 2020). Additionally, grid configurations are controlled using the vertical grid nesting method of Daniels et al. (2016) and turbulence development at intermediate resolutions is improved using the cell perturbation method of Munoz-Esparza et al. (2015). Multiscale simulations are extremely challenging to configure due to the sensitivity of each nested domain to its configuration and to the configuration of its parent domain(s). This dissertation also begins to investigate the model sensitivity to grid resolution and surface boundary condition, which is integral information for modelers configuring the nested domains of future multiscale simulations.Multiscale simulations are demonstrated for the prediction of transport and mixing of a tracer gas (SF6) released in the central business district of Oklahoma City during the Joint Urban 2003 field campaign. The simulations use either 5 or 6 nested domains with horizontal resolutions that range from several kilometers for the outermost domain to 2~m for the innermost domain. The multiscale simulations are compared with microscale-only simulations and with observations of wind speed, wind direction, and SF6 concentrations. The microscale-only simulations use idealized lateral boundary conditions and are configured using local meteorological observations from the field campaign. The multiscale simulation, which is configured independent of local observations, shows similar model skill predicting wind speed and wind direction, and improved skill predicting SF6 concentrations and turbulence kinetic energy when compared with the microscale-only simulations. Additionally, the multiscale simulation includes the effects of large-scale flow features and turbulence that the microscale-only simulations are incapable of resolving, which is shown to have a dramatic effect on predictions of transport and mixing. The analysis of simulations in this dissertation demonstrates the potential for multiscale simulations to improve predictions of transport and mixing over highly complex terrain and enable microscale simulations where local observations are not available.

The dissertation investigates buoyancy effects in turbulent bluff-body wakes that evolve in stratified fluids. The investigation utilizes high-resolution numerical simulations and employs a body-inclusive approach to describe the flow from the body into the far wake unlike the usual temporal-model approximation of most prior stratified-wake simulations. The dissertation is composed of three main parts. The first part focuses on the dynamics of vorticity that accounts for the unexpected regeneration and increase of turbulence in the near-to-intermediate wake when stratification increases in the regime of low body Froude numbers. The second part characterizes buoyancy effects on the evolution of turbulent kinetic energy in a sphere wake at moderate Froude number and an intermediate Reynolds number. The third part concerns the decay of a disk wake at relatively high Reynolds number and a wide range of Froude numbers, constitutes the major contribution of this thesis, and is summarized below.Large-eddy simulations (LES) of flow past a disk are performed at Re = UbLb/ν = 50,000 and at Fr = Ub/NLb = ∞,50,10,2; Ub is the free-stream velocity, Lb is the disk diameter, ν is the fluid kinematic viscosity, and N is the buoyancy frequency.In the axisymmetric wake in a homogeneous fluid, it is found that the mean streamwise velocity deficit (U0) decays in two stages; U0 ∝ x−0.9 during 10 < x/Lb < 65 followed by U0 ∝∼ x−2/3. Consequently, none of the simulated stratified wakes is able to exhibit the classical 2/3 decay exponent of U0 in the interval before buoyancy effects set in. The turbulent characteristic velocity, taken as K1/2 with K the turbulent kinetic energy (TKE), satisfies K1/2 ∝∼ x−2/3 after x/Lb ≈ 10. Turbulent wakes are affected by stratification within approximately one buoyancy time scale (Ntb ≈ 1) after which, provided that RehFrh2 ≥ 1, we find 3 regimes: weakly stratified turbulence (WST), intermediately stratified turbulence (IST), and strongly stratified turbulence (SST). The regime boundaries are delineated by the turbulent horizontal Froude number Frh = u′h/NLHk; here, u′h and LHk are r.m.s horizontal velocity and TKE- based horizontal wake width. WST begins when Frh decreases to O(1), spans 1 < Ntb < 5 and, while the mean flow is strongly affected by buoyancy in WST, turbulence is not. Thus, while the mean flow transitions into the so-called non-equilibrium (NEQ) regime, turbulence remains approximately isotropic in WST. The next stage of IST, identified by progressively increasing turbulence anisotropy, commences at N tb ≈ 5 once F rh decreases to O(0.1). During IST, the mean flow has arrived into the NEQ regime with a constant decay exponent, U0 ∝ x−0.18, but turbulence is still in transition. The exponent of 0.18 for the disk wake is smaller than the approximately 0.25 exponent found for the stratified sphere wake. When F rh decreases by another order of magnitude to F rh ∼ O(0.01), the wake transitions into the third regime of SST that is identified based on the asymptote of turbulent vertical Froude number (Frv = u′h/Nlv) to a O(1) constant. During SST that commences at Ntb ≈ 20, turbulence is strongly anisotropic (u′z ≪ u′h), and, both u′h and U0 satisfy x−0.18 decay signifying the arrival of the NEQ regime for both turbulence and mean flow. Turbulence is patchy and temporal spectra are broadband in the SST wake.Energy budgets reveal that stratification has a direct and positive influence on the prolongation of wake life. During the WST/early-IST stage, energy budgets show that the mean buoyancy flux acts to augment the MKE before the additional augmentation by reduced turbulent production. On the other hand, during WST/early-IST, the decay of TKE is faster than the unstratified case because of negative buoyancy flux (a sink that serves to increase turbulent potential energy) and increased dissipation and, additionally, also by the reduced production. In the late-IST/early-SST stages, production is enhanced and, additionally, there is injection from turbulent potential energy so that the TKE decay slows down. Only in the SST stage, when NEQ is realized for both the mean and turbulence, the turbulent buoyancy flux becomes negative again, acting as a sink of TKE.

The current generation of axial turbomachines are the culmination of decades of experience, and detailed understanding of the underlying flow physics has been a key factor for achieving high efficiency and reliability. Driven by advances in numerical methods and relentless growth in computing power, computational fluid dynamics has increasingly provided insights into the rich fluid dynamics involved and how it relates to loss generation. This article presents some of the complex flow phenomena occurring in bladed components of gas turbines and illustrates how simulations have contributed to their understanding and the challenges they pose for modeling. The interaction of key aerodynamic features with deterministic unsteadiness, caused by multiple blade rows, and stochastic unsteadiness, i.e., turbulence, is discussed. High-fidelity simulations of increasingly realistic configurations and models improved with help of machine learning promise to further grow turbomachinery performance and reliability and, thus, help fluid mechanics research have a greater industrial impact. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Baroclinicity, which leads to height-dependent driving pressure gradients, occurs in various situations such as the flow transition between land and sea, and sloping terrain. It has been shown that baroclinicity modifies the structure of the atmospheric boundary layer. For example, negative shear baroclinicity creates additional turbulence at higher elevations, which might influence the energy entrainment into large wind farms. Here, we use large-eddy simulations to study the effect of baroclinicity-induced negative shear on the wind farm power production and energy entrainment into a large wind farm. In agreement with the literature, our simulations show that negative geostrophic wind shear significantly modifies the mean wind velocity in the atmospheric boundary layer. Specifically, for the cases considered in the study, the negative geostrophic shear causes a change in the mean velocity up to 2.3 m/s at hub height, which greatly alters the wind farm power production. Additionally, we demonstrate with an energy budget analysis that a wind farm does not necessarily benefit from the additional turbulence created by the negative geostrophic wind shear. The reason for this is that the baroclinicity-induced negative shear alters the height and strength of the low-level jet and creates an upward flux above the jet, limiting the energy entrainment into the wind farm. Our results show that wind resources are altered in the boundary layer due to negative geostrophic wind shear and should be considered in wind farm modeling and power forecasts.

The aim of this study is to calculate the pressure loss and the effect of turning vanes on the pressure loss incurred by the flow in a duct with a 90˚ sharp elbow using numerical fluid mechanics. The main focus this study was to calculate the effects of the number of turning vanes and the length of the turning vanes on the pressure loss. Computational Fluid Dynamics calculations have been carried out using ANSYS Workbench software. Two turbulence models have been used in these calculations. They are the standard k- and the k- turbulence models. The number and length of the vanes were changed in the study to calculate their effects on pressure loss. The length of the vanes was varied from 0mm to 400mm in steps of 100mm on both sides of the bend and the number of vanes was changed from 0 to 3. It was found that a single curved turning vane can reduce the pressure loss significantly. The pressure loss does not reduce further when the length of the vanes was extended. As the number of turning vanes increased beyond one, the predicted pressure loss starts increasing. The turning vanes in duct systems can be used in industries and factories to reduce the pressure loss.

Airfoils in various types are widely used in many devices subjected to fluid flows such as aircrafts, vehicles, turbines etc. Therefore, analyzing the fluid flow around an airfoil is one of the important subjects in fluid mechanics. In this study, the conservation equations of two dimensional compressible flow over standard airfoils were solved by using different numerical techniques. After a mesh independence study, applied mathematical model, numerical techniques and obtained results are confirmed with experimental results given in literature. Three different turbulence models, namely the k-w spalarat almaras and the reynolds stress models were used in the solutions. The performances of turbulence models were evaluated under the results obtained. The verified numerical model was also applied to the flow over different types of blades, including a special airfoil design. Velocity and pressure fields obtained around these airfoils were analyzed, and their aerodynamic performances in terms of the lift and drag coefficients were compared to each other at different angles of attack.

Quantification of pressure drop across stenotic arteries is a major element in the functional assessment of occlusive arterial disease. Accurate estimation of the pressure drop with a numerical model allows the calculation of Fractional Flow Reserve (FFR), which is a haemodynamic index employed for guiding coronary revascularisation. Its non-invasive evaluation would contribute to safer and cost-effective diseases management. In this work, we propose a new formulation of a reduced-order model of trans-stenotic pressure drop, based on a consistent theoretical analysis of the Navier-Stokes equation. The new formulation features a novel term that characterises the contribution of turbulence effect to pressure loss. Results from three-dimensional computational fluid dynamics (CFD) showed that the proposed model produces predictions that are significantly more accurate than the existing reduced-order models, for large and small symmetric and eccentric stenoses, covering mild to severe area reductions. FFR calculations based on the proposed model produced zero classification error for three classes comprising positive (≤ 0.75), negative (≥ 0.8) and intermediate (0.75 − 0.8) classes.

Air curtains (ACs) employ plane turbulent jets to separate two environments in terms of heat and mass transfer, while still allowing unrestricted access through the opening between these environments. Most previous studies focused on ACs discharged from nozzles located just above the opening. However, in some cases ACs have to be installed close to the ceiling at a substantial distance from the top of the opening. The AC blown downwards along the vertical wall then first resembles a wall jet and after reaching the top of the opening starts resembling a free jet. The present study analyzes the behavior and performance of an AC with upstream wall above the opening. 2D steady RANS CFD simulations are performed based on grid-sensitivity analyses and validation with experimental data for a wall jet and a free jet. The total opening height is 4 m and vertical walls of 0.5 m, 1 m and 2 m, partly closing this opening, are considered. AC performance is evaluated both with the separation efficiency η (based on infiltration) and the adapted separation efficiency η* (based on infiltration and exfiltration). It is shown that the presence of the wall reduces jet decay. The longer the wall, the larger the jet momentum over the opening height. This reduces infiltration and increases η, but it increases exfiltration and therefore decreases η*. In practice, the jet discharge velocity (jet momentum) will have to be adjusted to keep high η*.

International audience; A frequent configuration in computational fluid mechanics combines an explicit time advancing scheme for accuracy purposes and a computational grid with a very small portion of much smaller elements than in the remaining mesh. Two examples of such situations are the travel of a discontinuity followed by a moving mesh, and the large eddy simulation of high Reynolds number flows around bluff bodies where together very thin boundary layers and vortices of much more important size need to be captured. For such configurations, multi-stage explicit time advancing schemes with global time stepping are very accurate, but also very CPU consuming. In order to reduce this problem, the multirate time stepping approach represents an interesting improvement. The objective of such schemes, which allow to use different time steps in the computational domain, is to avoid penalizing the computational cost of the time advancement of unsteady solutions which would become large due to the use of small global time steps imposed by the smallest elements such as those constituting the boundary layers. In the present work, a new multirate scheme based on control volume agglomeration is proposed for the solution of the compressible Navier-Stokes equations equipped with turbulence models of flows around bluff bodies like a flow around a space probe model at Reynolds number 106, a circular cylinder at Reynolds number 8.4 × 106, and two tandem cylinders at Reynolds number 1.66 × 105 and 1.4 × 105.; Une configuration fréquente en mécanique des fluides computationnelle combine un schéma explicite d’avancée temporelle à des fins de précision et une grille de calcul avec une très petite partie d’éléments beaucoup plus petits que dans le maillage restant. Deux exemples de telles situations sont le déplacement d'une discontinuité suivi d'un maillage en mouvement, et la simulation par grand tourbillonnement d'un nombre de Reynolds élevé circule autour de corps arrondis où des couches limites très minces et des tourbillons de taille beaucoup plus importante doivent être capturés. Pour de telles configurations, les schémas d'avancement temporel explicite à plusieurs étapes à pas de temps global sont très précis, mais consomment également beaucoup de temps calcul. Afin de réduire ce problème, l’approche multirate représente une amélioration intéressante. L’objectif de l'usage de ces methodes, qui permettent d’utiliser différents pas de temps dans le domaine informatique, est d’éviter de pénaliser le coût en calcul de l’avancement en temps des solutions instables qui deviendraient importantes en raison de l’utilisation de petits pas de temps globaux imposés par les plus petits éléments. tels que ceux constituant les couches limites. Dans le présent travail, un nouveau schéma multirate basé sur l'agglomération en volume de contrôle est proposé pour la solution des équations de Navier-Stokes compressibles équipées de modèles de turbulence.

Particleboards are widely used in the artificial board market, which can be constructed from a variety of raw materials and require small amounts of energy to be produced. In the particleboard production process, forming machines play an important role as the key equipment for achieving continuous production. In recent years, airflow forming machines have received increasing attention in particleboard production lines because of their strong separation ability and low price. However, the internal flow field is complex and difficult to control, which affects the surface quality and strength of the particleboard. The most pressing technical difficulty is controlling the flow field characteristics of the airflow paver. At present, the research on this subject is conducted primarily through repeated experiments, which entail long research periods and high processing costs. To reduce human and financial costs, in this study, Computational Fluid Dynamics (CFD) is employed to investigate the flow field and the gas-solid two-phase flow field coupled with particle movement of an airflow forming machine. The accuracy of the calculation model is verified by comparing characteristic point velocities obtained from experimental analysis and a simulation. The simulation results show that in practical production, the frequency of a negative pressure fan should be greater than 27 Hz. It is necessary to set the shoulder properly, and the slab smoothness can be improved by moving the shoulder back on the premise of meeting the strength requirements of the box. The distance between the shoulders of the box body should be less than 2570 mm, and particles with uniform diameter should be added to the paving box to reduce the turbulence effect, improve the quality of particle forming and provide actual particleboard production with a solid theoretical foundation.

A quasi-one-dimensional (1D) mathematical model coupled with Computational Fluid Dynamics (CFD) simulations of a water ejector is presented. Using data from CFD simulations, the mathematical model was used to calculate the friction loss coefficients of the ejector components, to predict its maximum efficiency point and to delimit its envelope of operation. The CFD approach was validated with experimental data and employed the finite element method to test the main turbulence models found in the literature (k-e, k-ω and k-ω SST) for incompressible-flow ejectors. A set of operational conditions (OP) was tested and results show that the k-ω SST turbulence model is the most suitable to capture the ejector flow characteristics in all OP. In addition, for higher entrainment ratio ( M ) values, it was observed a possible correlation between how well the boundary layer can be solved and how the model is able to capture the ejector efficiency curve. Moreover, for lower M values, another possible correlation may be stated between how the turbulence model is able to capture the velocity profile.

Traffic sign boards are often blown away by strong winds, seriously endangering the safety of vehicles and pedestrians. To increase their resistance to strong winds, sign boards are perforated. Using computational fluid dynamics simulations, the wind load resistance of traffic signs with holes was optimised. By comparing the solutions to different turbulence models with empirical results, it was found that the simulation results of the re-normalisation group (RNG) model have the smallest error. Therefore, the RNG model is used to simulate the wind load of traffic sign boards with different perforation diameters and different hole spacings under different wind speeds. By analysing the wind pressure distribution on the surface of the perforated traffic sign board, the perforation scheme for different regions of the sign board under different wind loads was obtained. The results show that reasonable perforation diameters and hole spacings can reduce the wind load and improve the wind load resistance of sign boards. This study provides decision-makers with useful information for installing traffic signs in areas affected with strong winds, thereby improving the wind resistance of traffic signs and ensuring traffic safety.

BiMEP-Biscay Marine Energy Platform- eta Mutriku Wave Energy Plant-eko azpiegituretan itsas energiaren inguruko ikerkuntza egiten da, itsas baldintza errealetan. Bilboko Ingeniaritza Eskolako Fluidoen Mekanikako laborategian dagoen olatu-kanala (12,5 × 0,6 × 0,7 m, luzera × zabalera × sakonera) azpiegitura horietan izaten diren baldintzak erreproduzitzeko gai da, eskala txikiago batean. Olatu-kanal horrek, pistoi motako olatu-sorgailu bat erabiliz, olatu monokromatiko eta pankromatiko mota desberdinekin lan egiteko aukera eskaintzen du. Ultrasoinuak erabiltzen dituzten zenbait zundak ur-gainazalaren desplazamendu bertikala neurtzen dute, eta tankearen amaieran kokatuta dagoen hondartzak, parabola-formadunak, olatuaren energia disipatzen du horren islapena murriztuz. "Reynolds Averaged Navier Stokes" (RANS) ekuazioetan oinarritutako zenbakizko modelo bat sortu da Star-CCM+ kode komertziala erabiliz, gainazal askean gertatzen diren fenomenoak simulatzeko. Zenbakizko modelo horren balioztatzea aurkezten da artikulu honetan, sakonera, olatu-altuera, uhin-luzera eta periodo desberdinak bateratuta eta egindako esperimentu sortarekin konparatuta. Emaitza guztiak fluxu potentzialaren teoriatik lortutako emaitza analitikoekin batera aztertu dira. Lan honetan aurkezten diren esperimentuek kanal horren eraginkortasunaren mugak ezartzen dituzte, olatuen sorkuntzari, hedapenari eta suntsipenari dagokienez. Etorkizunean egingo diren ikerkuntza-lanetako parametroak ezartzeko ere baliogarria izan da lan hau: egitura flotagarrien eta olatuen arteko interakzioa, olatu energiaren bihurgailuak eta ainguratze- eta amarradura-sistemak aztertuko dira.; A wave flume of 12.5 × 0.6 × 0.7 m (length × width × height) able to reproduce the ocean conditions of the most representative research facilities in the Basque Country (BiMEP-Biscay Marine Energy Platform and Mutriku Wave Energy Plant) has been installed at the laboratory of Fluid Mechanics of the Faculty of Engineering in Bilbao. This new facility has the capacity of producing a wide range of monochromatic and panchromatic waves by a piston-type wavemaker.Several ultrasonic wave probes measure the surface elevation, and the wave energy is dissipated in a passive parabolic beach in order to diminish significantly the reflection along the flume. A numerical model based on Reynolds Averaged Navier Stokes (RANS) equations has been developed to represent the turbulence and Eulerian Volume of Fluid (VOF) unsteady approach in STAR-CCM+ CFD code to track the evolution of the free surface. This numerical model has been validated with the corresponding experimental campaign covering a wide range of depths, wave heights, wavelengths and periods.The results are analysed together with the analytical solution coming from the potential flow theory. The experiments carried out in the present work establish the operational limits of the wave flume in terms of wave generation, propagation and extinction, defining the operational range of future experimental and computational campaigns where wave interaction with floating structures, wave energy converters and mooring systems will be studied.

The present project consists on the computational study and resolution of the Navier-Stokes equations and the physical phenomena involved. The main objective is the development of C++ programming codes to solve flow’s governing equations using numerical methods. The project comprises the fluid dynamic and thermal study and analysis of both laminar and turbulent regimes. In addition to that, in case of turbulent flow, there has been selected to implement a RANS turbulence model called Spalart-Allmaras. The computational codes developed will be used to simulate the study cases LID Driven Cavity, LID Differentially Heated and Square Cylinder for the laminar regime and a supersonic pipe in case of the turbulent part. Additionally, the results obtained will be extensively analysed and verified using scientific publications.

In rotary kilns in grate-kiln systems for iron ore pelletizing, a long and stable jet flame is needed to ensure a high quality of the pellets. The primary jet issuing from the nozzle interacts with two asymmetric co-flows creating a very complex flow. In order to better understand and eventually model this flow with quality and trust, simplified cases need to be studied. In this work, a simplified and virtual model is built based on a down-scaled kiln model established in a previous experimental work. The aim is to numerically study the jet development as a function of position and Reynolds number (Re). The numerical simulations are carried out with the standardk-εmodel, and quite accurate velocity profiles are obtained while the centerline decays and spreading of the passive scalars are over predicted. The model is capable of predicting a Re dependency of the jet development. With increasing Re, the jet is longer while it generally decays and spreads faster resulting from the stronger shear between the jet and co-flows and the stronger entrainment from the recirculation zone. This recirculation found in the simulations restrain the momentum spreading in the spanwise direction, leading to a slower velocity spreading with higher Re. For further validation and understanding, more measurements in the shear layer and simulations with more advanced turbulence models are necessary.

We address the task of modelling numerically turbulent flows within random arrays of circular cylinders, relevant for several industrial and environmental applications. Numerical simulations are employed to model infinite domains of randomly placed emergent and rigid cylinders validated by a laboratory database acquired by a PIV system. The main goals are: (i) to discuss the effect of the numerical domain size and the grid resolution on the first and second order moments and (ii) to characterise the spatial distribution of mean flow and turbulence variables in the drag-wake controlled stratum. Five domains of different sizes (9–44 cylinders) and four grid resolutions were independently tested. The results show that the time-averaged velocity field and the Reynolds stress tensor were not significantly affected by the size of the tested numerical domains. The analysis of the grid resolution influence shows how the results improve with mesh refinement, while none of the tested meshes produces un-physical results. The present work provides guidance on the acceptable compromises, in terms of mesh resolution and domain size, when predicting, with eddy resolving computational fluid mechanics tools, first and second-order moments of turbulent flows within infinite arrays or randomly placed cylinders. © 2018 Elsevier Ltd 80 245 261 245-261

Topics related to the modeling of turbulent flow feature significant relevance in several areas, especially in engineering, since the vast majority of flows present in the design of devices and systems are characterized to be turbulent. A vastly applied tool for the analysis of such flows is the use of numerical simulations based on turbulence models. Thus, this work aims to evaluate the performance of several turbulence models when applied to classic problems of fluid mechanics and heat transfer, already extensively validated by empirical procedures. The OpenFOAM open source software was used, being highly suitable for obtaining numerical solutions to problems of fluid mechanics involving complex geometries. The problems for the evaluation of turbulence models selected were: two-dimensional cavity, Pitz-Daily, air flow over an airfoil, air flow over the Ahmed blunt body and the problem of natural convection between parallel plates. The solution to such problems was achieved by utilizing several Reynolds Averaged Equations (RANS) turbulence models, namely: k-ε, k-ω, Lam-Bremhorst k-ε, k-ω SST, Lien-Leschziner k-ε, Spalart-Allmaras, Launder-Sharma k-ε, renormalization group (RNG) k-ε. The results obtained were compared to those found in the literature which were empirically obtained, thus allowing the assessment of the strengths and weaknesses of the turbulence modeling applied in each problem.

Low-level jets (LLJs) are winds with high-shear and large wind energy potential. We perform large-eddy simulations (LES) with actuator line modeling of a turbine operating in a moderately stable boundary layer in the presence of LLJs. We find that the turbine tip and root vortices break down quickly when the LLJ is above the turbine rotor swept area. In contrast, the wake recovery is slow, and the vortices are stable when the LLJ is in the middle or even below the rotor swept area. The LLJ shear causes significant azimuthal variation in the external aerodynamic blade loading, increasing fatigue loading on the turbines. We observe that both tangential and axial forces on the blades are highest when the blade directly interacts with the LLJ. Azimuthal variation in the tangential forces on the blades is the highest when the LLJ is above the rotor swept area, i.e. when the turbine operates in the positive shear region of LLJ, with the blade tip interacting with the LLJ.