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The numerical simulation of turbulent flows is a subject of great practical importance to scientists and engineers. The difficulty in achieving predictive simulations is perhaps best illustrated by the wide range of approaches that have been developed and are still being used by the turbulence modeling community. In this book the authors describe one of these approaches, Implicit Large Eddy Simulation (ILES). ILES is a relatively new approach that combines generality and computational efficiency with documented success in many areas of complex fluid flow. This book synthesizes the theoretical basis of the ILES methodology and reviews its accomplishments. ILES pioneers and lead researchers combine here their experience to present a comprehensive description of the methodology. This book should be of fundamental interest to graduate students, basic research scientists, as well as professionals involved in the design and analysis of complex turbulent flows.
This book addresses both the fundamentals and the practical industrial applications of Large Eddy Simulation (LES) in order to bridge the gap between LES research and the growing need to use it in engineering modeling.
First concise textbook on Large-Eddy Simulation, a very important method in scientific computing and engineering From the foreword to the third edition written by Charles Meneveau: "... this meticulously assembled and significantly enlarged description of the many aspects of LES will be a most welcome addition to the bookshelves of scientists and engineers in fluid mechanics, LES practitioners, and students of turbulence in general."
This book presents a comprehensive overview of the mathematics and physics behind the simulation of turbulent flows and discusses in detail (i) the phenomenology of turbulence in fluid dynamics, (ii) the role of direct and large-eddy simulation in predicting these dynamics, (iii) the multiple considerations underpinning subgrid modelling, and, (iv) the issue of validation and reliability resulting from interacting modelling and numerical errors.
In the LEE of high Reynolds number wall-bounded flows, wall modeling is needed to alleviate the severe near-wall resolution requirement. Simple algebraic models such as the instantaneous log-law are inadequate for predicting complex flows with strong pressure gradients and separation. We have explored two classes of wall models: those based on the turbulent boundary-layer (TBL) equations and those based on control theory. Recent application of the TBL equation model to LEE of the flow over a cylinder at super-critical Reynolds number is discussed. The emphasis of the report is on control based wall modeling, in which sub-optimal control strategy is used to find the wall stresses that will force the outer LEE toward a target profile. Results from channel-flow simulation indicate that in order to obtain the correct mean velocity profile (the log law), the wall stresses must not only model the physics but also compensate for numerical and SGS modeling errors. The data generated by this sub-optimal control strategy are then used to derive a linear stochastic estimate model. The mathematical formulation and issues of key importance in control-based wall modeling are detailed. Efforts towards a predictive and inexpensive wall model in the control framework are detailed.
The field of Large Eddy Simulations is reaching a level of maturity that brings this approach to the mainstream of engineering computations, while it opens opportunities and challenges. The main objective of this volume is to bring together leading experts in presenting the state-of-the-art and emerging approaches for treating complex effects in LES. A common theme throughout is the role of LES in the context of multiscale modeling and simulation.
The LES-method is rapidly developing in many practical applications in engineering The mathematical background is presented here for the first time in book form by one of the leaders in the field
The main purpose of this thesis has been to contribute to the development of methodologies for wall modeling Large Eddy Simulations (LES) of wall-bounded flows, especially those at high Reynolds numbers. This flow configuration is widely found in a vast range of industrial applications. Unfortunately, given the physical nature of boundary layers, their accurate numerical resolution can be computationally unaffordable. Wall modeling aims at reproducing the inner layer effects on the flow without resolving it explicitly. This allows performing accurate numerical simulations of high Reynolds number wall-bounded flows at a fraction of the cost that would be incurred if the inner layer was temporally and spatially resolved. This work comprises six chapters. The first one is an introduction to the existing Computational Fluid Dynamics (CFD) approaches, from the most accurate and general methodologies to the most simplified and specific techniques. The second chapter introduces relevant physical magnitudes to be analyzed to ensure the reliability of a given high fidelity CFD simulation. Spatial and temporal aspects, both crucial for a correct and accurate resolution of a turbulent flow, are considered. In the third chapter, a Two-Layer wall shear stress model (TLM) for LES and suitable for non-equilibrium flows and complex geometries is presented. Wall shear stress models in general, and RANS-based wall models (WM) in particular, are affected by the "log-layer mismatch" (LLM) and the resolved Reynolds stresses (RRS) inflow problems which undermine the quality of the WM numerical predictions. The model presented in this work features a temporal filter in the WM/LES interface which allows solving both problems at once with a single and low-computational-cost step. Until now, these two problems have been dealt with separately with different techniques, which in some cases were complex and computationally expensive. On the other hand, a methodology intended to determine the optimal temporal filter length is proposed and validated in equilibrium and non-equilibrium conditions. This new technique is based on the velocity power spectrum which reveals the flow characteristic time-scales in the near-wall region. According to the results obtained in the validation tests, it is concluded that for RANS-based TLM methods, time-resolved frequencies higher than the energy-containing/inertial range limit must be filtered. In chapter four, the mathematical model of the TLM, based on the URANS equations, is presented. Moreover, its numerical resolution through the finite volume method is developed and finally summarized in a flow-chart. Then, in chapter five, the algorithmic implementation of the numerical model described in chapter four is presented. The TLM is a fully operational and independent CFD solver based on the URANS equations, which has been developed from scratch. Given that the primary objective of wall modeling is reducing the computational costs, an efficient algorithmic and parallel implementation is a key aspect of the global modeling strategy. Thus, the parallel efficiency is evaluated through a strong scalability test. Good results are obtained although some aspects to be improved are identified. Finally, in the last chapter, general conclusions concerning the whole work are given together with future research proposals aimed at going further in the methodologies studied in this thesis.