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.

Zusammenfassung
Selected Papers from the First ERCOFTAC Workshop on Direct and Large-Eddy Simulation

Inhalt
Structures from Simulations.- Large-Scale Structures in the Turbulent Flow Near a Right-Angled Corner.- Very-Large-Scale Structures in DNS.- Eddy Structures in a Simulated Plane Turbulent Jet Educed by Pattern Recognition Analysis.- Subgrid-Scale Modelling.- Experimental Study of Similarity Subgrid-Scale Models of Turbulence in the Far-Field of a Jet.- Direct and Large Eddy Simulations of Round Jets.- Subgrid-Scale Models based upon the Second-Order Structure-Function of Velocity.- Significant Terms in Dynamic SGS-Modeling.- Assessment of the Generalised Normal Stress and the Bardina Reynolds Stress Subgrid-Scale Models in Large Eddy Simulation.- Subgrid-Scale Modelling in the Near-Wall Region of Turbulent Wall-Bounded Flows.- Two-dimensional Simulations with Subgrid Scale Models for Separated Flows.- A Priori Test of a Subgrid Scale Stress Tensor Model Including Anisotropy and Backscatter Effects.- Subgrid-modelling in LES of Compressible Flow.- Stratified and Atmospheric Flows.- Sheared and Stably Stratified Homogeneous Turbulence: Comparison of DNS and LES.- Direct Numerical Simulation of a Stably Stratified Turbulent Boundary Layer.- A Neutral Stratified Boundary-Layer: A Comparison of Four Large-Eddy Simulation Computer Codes.- The Large-Eddy Simulation of Dispersion of Passive and Chemically Reactive Pollutants in a Convective Atmospheric Boundary Layer.- Numerical Simulation of Breaking Gravity Waves below a Critical Level.- Transition.- Stability of the Natural-Convection Flow in Differentially Heated Rectangular Enclosures with Adiabatic Horizontal Walls.- Direct Simulation of Breakdown to Turbulence Following Oblique Instability Waves in a Supersonic Boundary Layer.- Mechanisms and Models of Boundary Layer Receptivity Deduced from Large-Eddy Simulation of By-pass Transition.- Receptivity by Direct Numerical Simulation.- Direct Numerical Simulation of Transition in a Spatially Growing Compressible Boundary Layer Using a New Fourier Method.- Complex Geometries.- Large-Eddy Simulation of Flow and Heat Transfer in Compact Heat Exchangers.- Large-Eddy Simulation of Turbulent Flow through a Straight Square Duct and a 180° bend.- Numerical Simulation of Turbulent Flow over a Wavy Boundary.- Large-Eddy Simulation of Turbulent Boundary Layer Flow over a Hemisphere.- Large-Eddy Simulation of Compound Channel Flow with One Floodplain at Re ? 42000.- Large-Eddy Simulation Applied to an Electromagnetic Flowmeter.- Compressible, Reacting and Thermal Flows.- On the Formation of Small Scales in a Compressible Mixing Layer.- Direct Simulation of Turbulence Phenomena in Compressible Boundary Layers.- DNS of a M = 2 Shock Interacting with Isotropic Turbulence.- Direct and Large Eddy Simulations of Chemically Reacting Flows.- Flow Mechanisms and Heat Transfer in Rayleigh-Bénard Convection at Small Prandtl Numbers.- Direct and Large-Eddy Simulation of Transient Buoyant Plumes: a Comparison with Experiment.- Numerical Investigation of Turbulent Structures in Thermal Impinging Jets.- Numerical Simulations of 2-D Turbulent Natural Convection in Differentially Heated Cavities of Aspect Ratios 1 and 4.