Large-Eddy simulation (LES) has become an important tool in computational fluid mechanics but still is far from replacing Reynolds-averaged Navier-Stokes (RANS) approaches. The present work compares combustion models for LES and RANS derived from the same physical assumptions. Thus a direct comparison of results from both approaches for a combusting flow becomes possible. The models are based on the assumption of a fractal shape of the flame surface, leading to the Lindstedt-Vaos model in RANS. Its generalization to LES is presented here. Both RANS and LES models are validated with data from a turbulent Bunsen flame to evaluate their sensitivity to turbulence level and length scale. The predicted turbulent burning velocity shows a very similar behavior in both models. The models are also tested with a second validation configuration, the combusting flow over a backward-facing step. This flow clearly shows the different behavior of RANS and LES methods in unsteady flows containing large coherent turbulent structures.

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