This thesis constitutes detailed computational investigation on ow through the passages of a centrifugal compressor used for turbocharging applications. Given the dynamic nature of operation of the turbocharger, it becomes necessary to under- stand the ow that occurs within the blade passages and its e ect on performance. CFD is an established computational technique wherein the ow is dissected to fun- damental levels and a detailed picture is presented, application of this technique with limited and diverse sense towards understanding of ows through a turbocharger compressor has been successfully carried out by many before. This work presented attempts to address many of the lacuna reported and carries forward the work of several researchers to ll in the gaps. The complexity of the geometry of the blade shape poses many challenges in model- ing within the virtual space, an e ective way to overcome the obstacles is presented as a part of this work. Grid generation of the impeller and casing are discussed and adaptive approach is followed with generation of hexahedral grids for the impeller whereas tetrahedral for the casing. Since the grids of the impeller and its casing are di erent, ways of interfacing between the two domains in a CFD environment is discussed. An industry standard implicit 3D RANS solver was used to carry out the simula- tions. The importance of use of boundary conditions for the domain at unsteady operating points is presented in detail. On the choice made for turbulence model that governs the validity of the solution obtained, an extensive literature survey of the relevant topic as applicable for centrifugal compressors is presented and logic of the choice made for the present work is discussed. Menter's two equation SST-k! model emerges as the clear choice to be used even though the di erence in perfor- mance predictions by other turbulence models are insigni cant. Dynamics of ow at optimum design point, surge and choke of the compressor are presented in detail. With the geometry modeled with a tip clearance and the casing included within the simulation environment, it can be seen that the performance predicted is closer to actual at all operating points. A study of behavior of the compressor at extreme o design points is carried out and it can be seen that it depicts the trends that are seen in experimental works available in open literature. The distortion of pressure within the vaneless di user and the inviscid nature of the ow within the volute space are e ectively captured and an in depth analysis is carried out to uncover new patterns. A parametric study involving important geometric features such as the tip clearance and wrap angles are conducted leading to discovery of anomalies. The work summarizes to point out that the investigation carried out with the CFD simulations comprehensively leads to uncovering of ow dynamics within a complex system such as the centrifugal compressor within the limits of numerical analysis.

O presente trabalho trata de construir um modelo computacional utilizando o método dos volumes finitos para malhas não-estruturadas, a fim de se calcular a carga hidráulica num meio poroso, considerando este meio não homogêneo e anisotrópico. A anisotropia é uma característica de muitos materiais encontrados na natureza e depende da propriedade estudada no meio. Primeiramente apresenta-se a dedução da equação do transporte advectivo dispersivo e a formulação matemática para a equação de Laplace, esta última utilizada para o cálculo da carga hidráulica. Em seguida, apresenta-se o algoritmo de solução de um programa computacional em linguagem C++ que permite calcular a velocidade do fluxo em cada face de um volume de controle. Finalmente são feitos vários testes para validação do código computacional utilizado, o que levou a crer que o método utilizado é eficaz para os tipos de malhas testados, apresentando algumas diferenças quanto ao erro da solução. / The present work build a computational model using the finite volumes method for unstructured meshes, with the purpose of calculating the hydraulic load in a porous medium, considering it material non - homogeneous and anisotropic. The Anisotropy is a characteristic of many materials found in the nature and it depends on the property studied in this material. First, we present the deduction of the equation of advective-dispersive transport and the mathematical formulation for the Laplaces equation, this last one used for the calculation of the hydraulic load. Soon afterwards, we present the solution algorithm of a computational program in the C++ language that allows to calculate the speed of the flow in each face of the control volume. Finally several tests for validation of the code are made, which makes it that the plausible to assume method is effective for the types of meshes tested, presenting some differences for the wrong solution.

Manufatura Aditiva, também conhecida por Impressão 3D, é um processo baseado na sobreposição de camadas para produzir um objeto físico. Os dados para a produção desse objeto vêm de um modelo geométrico tridimensional, geralmente representado por uma malha de triângulos. Um dos principais procedimentos no processo de produção é fatiar a malha triangular e gerar uma série de contornos, os quais representam as camadas do objeto. Há diversas estratégicas para fatiar malhas triangulares, porém, a maior parte dos trabalhos na literatura foca-se em problemas como a qualidade do modelo, melhorias específicas no processo de fatiamento e uso de memória; poucos trabalhos, no entanto, abordam o problema por uma perspectiva de complexidade algorítmica. Algoritmos propostos atualmente para este problema executam em tempo O(n² + k²) ou O(n² + nlognk); o algoritmo proposto nesta dissertação possui complexidade O(nk) para uma entrada com n triângulos e k planos e, com K é o número médio de planos que cortam cada triângulo nesta entrada específica. O algoritmo proposto, chamado de Fatiamento por Estocada (FE) é comparado teórica e experimentalmente com alguns dos métodos conhecidos na literatura e os resultados mostram melhora considerável em tempo de execução. / Additive Manufacturing, also known as 3D printing, is a process based on the addition of sucessive layers in order to build a physical object. The data for building this object come from geometric 3D model, usually represented by a triangle mesh. One of the main procedures in this process is to slice the triangle mesh and output a sequence of contours, representing each one of the layers of the object. There are many strategies for slicing meshes, however, most of the current literature is concerned with ad hoc issues such as the quality of the model, specific improvements in the slicing process and memory usage, whereas few of them address the problem from an algorithmic complecity perspective. While current algorithms for this problem ruin in O(n² + k²) or O(n² + nlognk), the proposed algorithm runs in O(nk), for a given input with n triangles, k planes and where k is the average number of slices cutting each triangle in this specific input. This is asymptotically the best that can be achieved under certain fairly common assumptions. The proposed algorithm, called here Slicing by Stabbing (SS), was compared both theoretically and experimentally against known methods in the literature and the results show considerable improvement in execution time.

Manufatura Aditiva, também conhecida por Impressão 3D, é um processo baseado na sobreposição de camadas para produzir um objeto físico. Os dados para a produção desse objeto vêm de um modelo geométrico tridimensional, geralmente representado por uma malha de triângulos. Um dos principais procedimentos no processo de produção é fatiar a malha triangular e gerar uma série de contornos, os quais representam as camadas do objeto. Há diversas estratégicas para fatiar malhas triangulares, porém, a maior parte dos trabalhos na literatura foca-se em problemas como a qualidade do modelo, melhorias específicas no processo de fatiamento e uso de memória; poucos trabalhos, no entanto, abordam o problema por uma perspectiva de complexidade algorítmica. Algoritmos propostos atualmente para este problema executam em tempo O(n² + k²) ou O(n² + nlognk); o algoritmo proposto nesta dissertação possui complexidade O(nk) para uma entrada com n triângulos e k planos e, com K é o número médio de planos que cortam cada triângulo nesta entrada específica. O algoritmo proposto, chamado de Fatiamento por Estocada (FE) é comparado teórica e experimentalmente com alguns dos métodos conhecidos na literatura e os resultados mostram melhora considerável em tempo de execução. / Additive Manufacturing, also known as 3D printing, is a process based on the addition of sucessive layers in order to build a physical object. The data for building this object come from geometric 3D model, usually represented by a triangle mesh. One of the main procedures in this process is to slice the triangle mesh and output a sequence of contours, representing each one of the layers of the object. There are many strategies for slicing meshes, however, most of the current literature is concerned with ad hoc issues such as the quality of the model, specific improvements in the slicing process and memory usage, whereas few of them address the problem from an algorithmic complecity perspective. While current algorithms for this problem ruin in O(n² + k²) or O(n² + nlognk), the proposed algorithm runs in O(nk), for a given input with n triangles, k planes and where k is the average number of slices cutting each triangle in this specific input. This is asymptotically the best that can be achieved under certain fairly common assumptions. The proposed algorithm, called here Slicing by Stabbing (SS), was compared both theoretically and experimentally against known methods in the literature and the results show considerable improvement in execution time.

O presente trabalho trata de construir um modelo computacional utilizando o método dos volumes finitos para malhas não-estruturadas, a fim de se calcular a carga hidráulica num meio poroso, considerando este meio não homogêneo e anisotrópico. A anisotropia é uma característica de muitos materiais encontrados na natureza e depende da propriedade estudada no meio. Primeiramente apresenta-se a dedução da equação do transporte advectivo dispersivo e a formulação matemática para a equação de Laplace, esta última utilizada para o cálculo da carga hidráulica. Em seguida, apresenta-se o algoritmo de solução de um programa computacional em linguagem C++ que permite calcular a velocidade do fluxo em cada face de um volume de controle. Finalmente são feitos vários testes para validação do código computacional utilizado, o que levou a crer que o método utilizado é eficaz para os tipos de malhas testados, apresentando algumas diferenças quanto ao erro da solução. / The present work build a computational model using the finite volumes method for unstructured meshes, with the purpose of calculating the hydraulic load in a porous medium, considering it material non - homogeneous and anisotropic. The Anisotropy is a characteristic of many materials found in the nature and it depends on the property studied in this material. First, we present the deduction of the equation of advective-dispersive transport and the mathematical formulation for the Laplaces equation, this last one used for the calculation of the hydraulic load. Soon afterwards, we present the solution algorithm of a computational program in the C++ language that allows to calculate the speed of the flow in each face of the control volume. Finally several tests for validation of the code are made, which makes it that the plausible to assume method is effective for the types of meshes tested, presenting some differences for the wrong solution.

Computing 3D high lift flows has been a challenge to the CFD community because of three important reasons: complex physics, complex geometries and large computational requirements. In the recent years, considerable progress has been made in understanding the suitability of various CFD solvers in computing 3D high lift flows, through the systematic studies carried out under High Lift Prediction workshops. The primary focus of these workshops is to assess the ability of the CFD solvers to predict CLmax and αmax associated with the high lift flows, apart from the predictability of lift and drag of such flows in the linear region. Now there is a reasonable consensus in the community about the ability of the CFD solvers to predict these quantities and fresh efforts to further understand the ability of the CFD solvers to predict more complex physics associated with these flows have already begun. The goal of this thesis is to assess the capability of the computational methods in predicting such complex flow phenomena associated with the 3D High-Lift systems. For evaluation NASA three element Trapezoidal wing configuration which poses a challenging task in numerical modeling was selected. Unstructured data based 3D RANS solver HiFUN (HiFUN stands for High Resolution Flow Solver for UNstructured Meshes) is used in investigating the high lift flow. The computations were run fully turbulent, using the one equation Spalart-Allmaras turbulence model. A summary of the results obtained using the flow solver HiFUN for the 3D High lift NASA Trapezoidal wing are presented. Hybrid unstructured grids have been used for the computations. Grid converged solution obtained for the clean wing and the wing with support brackets, are compared with experimental data. The ability of the solver to predict critical design parameters associated with the high lift flow, such as αmax and CLmax is demonstrated. The utility of the CFD tools, in predicting change in aerodynamic parameters in response to perturbational changes in the configuration is brought out. The solutions obtained for the high lift configuration from two variants of the Spalart-Allmaras turbulence model are compared. To check the unsteadiness in the flow, particularly near stall, unsteady simulations were performed on static grid. Lastly, hysteresis on lower leg of lift curve is discussed, the results obtained for quasi-steady and dynamic unsteady simulations are presented. Inferences from the study on useful design practices pertaining to the 3D high lift flow simulations are summarized.

In this thesis, an approach is presented for the generation of grids suitable for the simulation of high Reynolds number viscous flows in complex three-dimensional geometries. The automatic and reliable generation of such grids is today on the biggest bottlenecks in the industrial CFD simulation environment.<p><p>In the proposed approach, unstructured tetrahedral grids are employed for the regions far from the viscous boundaries of the domain, while semi-structured layers of high aspect ratio prismatic and hexahedral elements are used to provide the necessary grid resolution inside the boundary layers and normal to the viscous walls. The definition of the domain model is based on the STEP ISO standard and the topological information contained in the model is used for applying the hierarchical grid generation parameters defined by the user. An efficient, high-quality and robust algorithm is presented for the generation of the unstructured simplicial (triangular of tetrahedral) part of the grid. The algorithm is based on the Delaunay triangulation and the internal grid points are created following a centroid or frontal approach. For the surface grid generation, a hybrid approach is also proposed similar to the volume.<p>Semi-structured grids are generated on the surface grid (both on the edges and faces of the domain) to improve the grid resolution around convex and concave ridges and corners, by aligning the grid elements in the directions of high solution gradients along the surface. A method is also developed for automatically setting the grid generation parameters related to the surface grid generation based on the curvature of the surface in order to obtain an accurate and smooth surface grid. Finally, a semi-structured prismatic/hexahedral grid generation algorithm is presented for the generation of the part of grid close to the viscous walls of the domain. The algorithm is further extended with improvements meant to increase the grid quality around concave and convex ridges of the domain, where the semi-structured grids are known to be inadequate.<p><p>The combined methodology is demonstrated on a variety of complex examples mainly from the automotive and aeronautical industry. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

In this paper we present two hierarchically preconditioned methods for the fast solution of mesh equations that approximate 2D-elliptic boundary value problems on unstructured quasi uniform triangulations. Based on the fictitious space approach the original problem can be embedded into an auxiliary one, where both the hierarchical grid information and the preconditioner by decomposing functions on it are well defined. We implemented the corresponding Yserentant preconditioned conjugate gradient method as well as the BPX-preconditioned cg-iteration having optimal computational costs. Several numerical examples demonstrate the efficiency of the artificially constructed hierarchical methods which can be of importance in the industrial engineering, where often only the nodal coordinates and the element connectivity of the underlying (fine) discretization are available.

An adaptive mesh redistribution method for efficient and accurate simulation of multi dimensional hyperbolic conservation laws is developed. The algorithm consists of two coupled steps; evolution of the governing PDE followed by a redistribution of the computational nodes. The second step, i.e. mesh redistribution is carried out at each time step iteratively with the primary aim of adapting the grid to the computed solution in order to maximize accuracy while minimizing the computational overheads. The governing hyperbolic conservation laws, originally defined on the physical domain, are transformed on to a simplified computational domain where the position of the nodes remains independent of time. The transformed governing hyperbolic equations are recast in a strong conservative form and are solved directly on the computational domain without the need for interpolation that is typically associated with standard mesh redistribution algorithms. Several standard test cases involving numerical solution of scalar and system of hyperbolic conservation laws in one and two dimensions are presented in order to demonstrate the accuracy and computational efficiency of the proposed technique.