Towards Large Eddy Simulation of flows in complex geometries

Abstract

The applications of Large Eddy Simulations (LES) to flows within or around complex geometries is becoming a realistic proposition with the use of massively parallel computers and improved computer architectures. LES is inherently three-dimensional and unsteady, and is therefore considerably more expensive than conventional Reynolds Averaged Simulations (RAS) models, but still affordable in comparison to Direct Numerical Simulation (DNS) models. For this reason, LES is best applied to flow problems were unsteady three dimensional effects are predominant and RAS models can be expected to fail. This contribution intends to give an overview of LES applied to flows in complex geometries and the advantages and problems associated with doing so. To illustrate this, results from simulations ranging from forced and decaying homogenous turbulence to flows involving unsteady and three-dimensional effects, such as vortex shedding behind a variety of bluff bodies, transonic flows over wing sections and supersonic flows around cylindrical afterbodies with base bleed are discussed. Comparisons are made with DNS and with a variety of RAS models from standard two-equation models to the more elaborate Reynolds stress models. Specifically, issues relating to sub-grid turbulence modelling and implementation on unstructured or non-uniform grids, are addressed.