LARGE-EDDY SIMULATION - A CRITICAL-REVIEW OF THE TECHNIQUE

Large-eddy simulation is being increasingly used as a means of both pr edicting the properties of specific turbulent flows and providing flow details which can be used like data to test and refine other turbulen ce-closure models. Although such simulations derive their credibility from the explicit resolution of large-scale turbulent eddies, they dep end upon a small-scale turbulence closure and must to some degree inhe rit the many uncertainties associated with turbulence closure. Most re sults obtained to date have been very encouraging, with examples of go od agreement with observations and insensitivity to the small-scale tu rbulence closure. However, there are some counter examples of incorrec t prediction in circumstances where the small-scale closure is critica l. The evidence from the simulations suggests that this critical behav iour may only occur in the regions of large-eddy simulation where matc hes to boundaries, or regions of statically stable fluid, are encounte red. In such regions an empirical approach dominates, and there is evi dence that the small-scale turbulence closure must represent stochasti c fluctuations of the unresolved stresses. Although there is a need to refine the small-scale turbulence models, it is clear from the promis e of current applications that, with the expected growth in computer p ower, this technique will have increasing breadth of application. Here the underlying assumptions and current practical implementations of t he technique are critically reviewed.