Direct and large Eddy simulation of turbulent premixed combustion

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The proposed research is on the use of Large Eddy and Direct Numerical Simulations (LES and DNS) to study turbulent premixed combustion.  Premixed combustion occurs where the fuel and oxidiser are mixed before they are burnt, and the combustion is then characterised by a locally varying turbulent flame speed which makes modelling the system difficult.  It is used in applications ranging from stationary gas turbines used for power generation to spark ignition IC engines.  It is particularly important in lean premixed combustion, a new approach to reducing emissions, but one that can lead to combution instabilities, damaging engines or causing shutdowns.  Both the local behaviour of the flames and the overall combustion process are controlled by the details of the turbulence-flame interactions, so a better understanding and modelling capability of these interactions are required.  The overall objectives here are to:   1. gain an inherently better understanding of premixed flame-turbulence interactions, and   2. ultimately develop an LES code capable of simulating the combustion within gas turbine combustors Both DNS and LES will be used in this work.  DNS solves the governing equations of the reacting flow in their entirety with no modelling required. It includes all of the scales of the turbulence and is consequently very computationally intensive -the proposed research involves using the upgraded Sharcnet facilities to look at parts of simple flames in regimes commonly seen in SI engines and large-scale gas turbines.  The results of the DNS runs will be used, not only to look at flame-turbulence interactions, but also to help develop models for the large eddy simulations.  LES resolves most of the turbulence in the flow; however, unlike DNS, it does not calculate the smallest scales of the turbulence and these small-scale "subgrid scale" features must then be modelled.  The resulting LES is then able to consider both the high Reynolds numbers and the complex geometries of real combustors while still including the real flame-turbulence behaviour.