Leonhard Kleiser - Böcker

Turbulence remains an unsolved problem even though we now know how to produce directly, with the help of modern supercomputers, accurate approximations to the equations that govern turbulent flows. The fact that we can predict some turbulence in this limited sense is nevertheless an enormous step towards the goal of full understanding. Direct numerical simulations and large-eddy simulations are these numerical solutions of turbulence, which reproduce with remarkable fidelity the statistical, structural and dynamical properties of physical turbulent and transitional flows. This volume contains selected papers from the First ERCOFTAC Workshop on Direct and Large-Eddy Simulation, which was held at the University of Surrey, Guildford from 28-30 March 1994. The variety of flows now accessible to simulation is evident throughout the volume. Many types of internal and external flow are represented, including some complex geometries of engineering or geophysical importance. The dynamically distinct regimes of incompressible and compressible flow, stratified, buoyant and other thermal flows, and chemically reacting flow are also covered.This book aims to reveal the current state of direct numerical simulation and large-eddy simulation of transitional and turbulent flows, and should be a valuable reference for all those with an active interest in these techniques.

Though there is no doubt about the importance of turbulent flow phenomena in engineering systems, the reliable prediction of turbulence remains an elusive goal. Direct numerical simulation of turbulent flows is possible at sufficiently low Reynolds numbers, while large-eddy simulation may be applied in the higher Reynolds number range of engineering importance. A six-month research programme organized in 1999 by the Isaac Newton Institute, Cambridge University, brought together experts from different communities to develop understandings of practical and fundamental problems in turbulence. This collection of papers, from one of the symposia held as part of the research programme in conjunction with ERCOFTAC, presents progress in the use of direct and large-eddy simulation. Describing simulations of turbulence and transition and approaches to the mathematics and physics of subgrid closures, the volume gives a clear overview of the status of this research area and its practical applications.

Though there is no doubt about the importance of turbulent flow phenomena in engineering systems, the reliable prediction of turbulence remains an elusive goal. Direct numerical simulation of turbulent flows is possible at sufficiently low Reynolds numbers, while large-eddy simulation may be applied in the higher Reynolds number range of engineering importance. A six-month research programme organised in 1999 by the Isaac Newton Institute, University of Cambridge, brought together experts from different communities to develop new understandings of practical and fundamental problems in turbulence. This collection of papers, from one of the symposia held as part of the research programme in conjunction with ERCOFTAC, presents current progress in the use of direct and large-eddy simulation. Describing novel simulations of turbulence and transition and innovative approaches to the mathematics and physics of subgrid closures, the volume gives a clear overview of the status of this important research area and its practical applications. This book should therefore be of interest to all researchers active in this area.

It is a truism that turbulence is an unsolved problem, whether in scientific, engin­ eering or geophysical terms. It is strange that this remains largely the case even though we now know how to solve directly, with the help of sufficiently large and powerful computers, accurate approximations to the equations that govern tur­ bulent flows. The problem lies not with our numerical approximations but with the size of the computational task and the complexity of the solutions we gen­ erate, which match the complexity of real turbulence precisely in so far as the computations mimic the real flows. The fact that we can now solve some turbu­ lence in this limited sense is nevertheless an enormous step towards the goal of full understanding. Direct and large-eddy simulations are these numerical solutions of turbulence. They reproduce with remarkable fidelity the statistical, structural and dynamical properties of physical turbulent and transitional flows, though since the simula­ tions are necessarily time-dependent and three-dimensional they demand the most advanced computer resources at our disposal. The numerical techniques vary from accurate spectral methods and high-order finite differences to simple finite-volume algorithms derived on the principle of embedding fundamental conservation prop­ erties in the numerical operations. Genuine direct simulations resolve all the fluid motions fully, and require the highest practical accuracy in their numerical and temporal discretisation. Such simulations have the virtue of great fidelity when carried out carefully, and repre­ sent a most powerful tool for investigating the processes of transition to turbulence.