In this thesis study, Detached Eddy Simulation turbulence model is studied in two dimension mainly for flow over single element airfoils in high Reynolds numbers to gain experience with model before applying it to a three dimensional simulations. For this aim, Spalart-Allmaras and standard DES ,DES97, turbulence models are implemented to parallel, viscous, hybrid grid flow solver. The flow solver ,Set2d, is written in FORTRAN language. The Navier-Stokes equations are discretized by first order accurately cell centered finite volume method and solved explicitly by using Runge-Kutta dual time integration technique. Inviscid fluxes are computed using Roe flux difference splitting method. The numerical simulations are performed in parallel environment using domain decomposition and PVM library routines for inter-process communications. To take into account the effect of unsteadyness after the convergence is ensured by local time stepping technique for four order magnitude drop in density residual, global time stepping is applied for 20000 iterations. The solution algorithm is validated aganist the numerical and experimental studies for single element airfoils in subsonic and transonic flows. It is seen that Spalart-Allmaras and DES97 turbulence models give the same results in the non-seperated flows. Grey area is investigated by changing $C_{DES}$ coefficient. Modeled Stress Depletion which cause reduction of eddy viscosity is observed.

Simulation and modelling of turbulent flows under influence of streamline curvature and system rotation have been considered. Direct numerical simulations have been performed for fully developed rotating turbulent channel flow using a pseudo-spectral code. The rotation numbers considered are larger than unity. For the range of rotation numbers studied, an increase in rotation number has a damping effect on the turbulence. DNS-data obtained from previous simulations are used to perform a priori tests of different pressure-strain and dissipation rate models. Furthermore, the ideal behaviour of the coefficients of different model formulations is investigated. The main part of the modelling is focused on explicit algebraic Reynolds stress models (EARSMs). An EARSM based on a pressure strain rate model including terms that are tensorially nonlinear in the mean velocity gradients is proposed. The new model is tested for a number of flows including a high-lift aeronautics application. The linear extensions are demonstrated to have a significant effect on the predictions. Representation techniques for EARSMs based on incomplete sets of basis tensors are also considered. It is shown that a least-squares approach is favourable compared to the Galerkin method. The corresponding optimality aspects are considered and it is deduced that Galerkin based EARSMs are not optimal in a more strict sense. EARSMs derived with the least-squares method are, on the other hand, optimal in the sense that the error of the underlying implicit relation is minimized. It is further demonstrated that the predictions of the least-squares EARSMs are in significantly better agreement with the corresponding complete EARSMs when tested for fully developed rotating turbulent pipe flow. / QC 20100825

In this study, the non-equilibrium Johnson and King Turbulence Model (JK model) is implemented in a three-dimensional, Navier-Stokes flow solver. The main program is a structured Euler/Navier-Stokes flow solver in which spatial discretization is accomplished by a finite volume formulation and a multigrid technique is used as a convergence accelerator. The aim is the validation of this in-house developed CFD (Computational Fluid Dynamics) tool with this enhanced enlarged capability in order to obtain a reliable flow solver that can solve flows over swept wings accurately. Various test cases were evaluated against reference solutions in order to demonstrate the accuracy of the newly implemented JK turbulence model. The selected test cases are NACA 0012 airfoil, ONERA M6 wing, DLR-F4 wing and two wings taken from the 3rd Drag Prediction Workshop. The solutions were analyzed and discussed in detail. The results show appreciably good agreement with the experimental data including force coefficients and surface pressure distributions.

Every type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies. This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example. After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin. Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units).

An unstructured explicit, Reynolds averaged Navier-Stokes solver is developed to operate on inviscid flows, laminar flows and turbulent flows and one equation Spalart-Allmaras turbulence modeling is implemented to the solver. A finite volume formulation, which is cell-center based, is used for numerical discretization of Navier-Stokes equations in conservative form. This formulation is combined with one-step, explicit time marching upwind numerical scheme that is the first order accurate in space. Turbulent viscosity is calculated by using one equation Spalart-Allmaras turbulence transport equation. In order to increase the convergence of the solver local time stepping technique is applied. Eight test cases are used to validate the developed solver,for inviscid flows, laminar flows and turbulent flows. All flow regimes are tested on NACA-0012 airfoil. The results of NACA-0012 are compared with the numerical and experimental data.

A three-dimensional, parallel, finite volume solver which uses Roe&#039 / s upwind flux differencing scheme for spatial and Runge-Kutta explicit multistage time stepping scheme for temporal discretization on unstructured meshes is developed for the unsteady solution of external viscous flow around rotating bodies. The main aim of this study is to evaluate the aerodynamic dynamic stability derivative coefficients for rotating missile configurations. Arbitrary Lagrangian Eulerian (ALE) formulation is adapted to the solver for the simulation of the rotation of the body. Eigenvalues of the Euler equations in ALE form has been derived. Body rotation is simply performed by rotating the entire computational domain including the body of the projectile by means of rotation matrices. Spalart-Allmaras one-euqation turbulence model is implemented to the solver. The solver developed is first verified in 3-D for inviscid flow over two missile configurations. Then inviscid flow over a rotating missile is tested. Viscous flux computation algorithms and Spalarat-Allmaras turbulence model implementation are validated in 2-D by performing calculations for viscous flow over flat plate, NACA0012 airfoil and NLR 7301 airfoil with trailing edge flap. The ALE formulation is validated in 2-D on a rapidly pitching NACA0012 airfoil. Afterwards three-dimensional validation studies for viscous, laminar and turbulent flow calculations are performed on 3-D flat plate problem. At last, as a validation test case, unsteady laminar and turbulent viscous flow calculations over a spinning M910 projectile configuration are performed. Results are qualitatively in agreement with the analytical solutions, experimental measurements and previous studies for steady and unsteady flow calculations.

The aim of this study is to develop a code that is capable of solving three-dimensional compressible flows which are viscous and turbulent, and parallelization of this code. Purpose of parallelization is to obtain a computational efficiency in time respect which enables the solution of complex flow problems in reasonable computational times. In the first part of the study, which is the development of a three-dimensional Navier-Stokes solver for turbulent flows, first step is to develop a two-dimensional Euler code using Roe flux difference splitting method. This is followed by addition of sub programs involving calculation of viscous fluxes. Third step involves implementation of Baldwin-Lomax turbulence model to the code. Finally, the Euler code is generalized to three-dimensions. At every step, code validation is done by comparing numerical results with theoretical, experimental or other numerical results, and adequate consistency between these results is obtained. In the second part, which is the parallelization of the developed code, two-dimensional code is parallelized by using Message Passing Interface (MPI), and important improvements in computational times are obtained.

En vue d’applications aux turbines éoliennes, cette thèse vise à étendre l’utilisation des méthodes de type domaines fictifs et en particulier la méthode de pénalisation pour la simulation de l’écoulement turbulent instationnaire autour d’obstacles de géométrie complexe.La modélisation de la turbulence instationnaire à nombres de Reynolds élevés a été abordée par des approches hybrides RANS/LES telles que la (DES) et la (DDES). Afin d’améliorer la prédiction, un modèle de paroi de type TBLE a été introduit.Après une brève présentation des méthodes et des outils mis en oeuvre, des simulations2D/3D sur la configuration de cylindre et du canal sont ensuite présentées, analysées et comparées aux résultats numériques et expérimentaux.Les résultats de simulation montrent la faisabilité et l’efficacité des modèles et de la méthode de couplage (DDES/TBLE). La dernière étude se concentre sur la simulation de l’écoulement d’air autour d’un profil de pale. Les réussites et les échecs des simulations numériques sont soulignés et étudiés.En conclusion, l’étude établit les fondements pour une future application dans le cas de l’écoulement autour d’un rotor éolien en mouvement. / In the perspective of application to wind turbine design, this thesis aims to extend theuse of fictitious domain methods and in particular the method of penalization for the simulation of unsteady turbulent flows around obstacles of complex geometry. The unsteady turbulence modeling at high Reynolds numbers was studied by hybrid approaches(RANS / LES) such as (DES) and (DDES). In order to improve the prediction, a wall model based on simplified Thin Boundary Layer Equations (TBLE) was introduced.After a brief presentation of the tools and methods implemented, full 2D / 3D computations on cylinder and channel configuration are then presented, analyzed and compared to numerical and experimental results.The simulation results show the feasibility and effectiveness of the proposed models and the coupling method (DDES / TBLE).The latest investigation focuses on the simulation of the flow around the airfoil of a wind turbine. The success and fails of the computations are highlighted and explained.

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In gas stirred steelmaking ladles, entrainment of slag into metal and vice versa takes place. The slag entrainment has been shown to abruptly increase the mass transfer rates of refining reactions through high temperature and water modeling studies of the past. However such an effect has not been correlated with the degree of entrainment, since the latter has not been quantified in terms of operating parameters like gas injection rate and fluid properties. Much of the past works are limited to finding the critical conditions for onset of entrainment. The difficulty lies in measuring the degree of entrainment in industrial ladles or even in a water model. Mathematical modeling is also challenging due to the complexity of the multiphase phenomena. So in this thesis, a modular mathematical modeling approach is presented wherein the phenomena of slag entrainment into metal is resolved into four aspects, models developed for each and finally integrated to study its role. The individual models are (1) multiphase large eddy simulations to simulate slag entrainment in a narrow domain that receives its boundary conditions from (2) single phase RANS simulation of a full ladle, (3) a Lagrangian particle tracking method to compute the residence times of slag droplets in metal phase and (4) a kinetic model that integrates the above three models to compute mass transfer rate as a function of degree of entrainment. Mass transfer rate predictions comparable to a literature correlation were obtained. This supports the modeling approach and also the assessment of role of various system parameters on entrainment characteristics. In essence, the present work shows a systematic approach to model and study the complex multiphase phenomena. / Thesis / Doctor of Philosophy (PhD) / The entrainment of liquid slag into liquid steel in gas stirred-steelmaking ladles is known to increase the rate of refining drastically. However, there is lack of correlation between degree of entrainment and ladle operating conditions, which this thesis addresses through mathematical modeling.