Comparison between LES results and experimental data in reacting flows

Resolved flow statistics extracted from large eddy simulations (LES) do not directly compare to unfiltered flow statistics determined, for example, from experiments. Scalar statistics in reacting flows are investigated here from a priori tests based on experimental data. Mean scalar fields are found to be quite well estimated from LES, taking into account mass-weighted statistics, but resolved variances are strongly affected by the filtering operation and decrease roughly linearly when the filter size Δ increases. Accordingly, subgrid scale scalar variances should be modelled to compare LES and experimental results. A simple gradient model is found to provide very good estimates of the mean subgrid scale variance of the progress variable.

Keywords:

• Large eddy simulations
• statistics
• comparison with experimental data
• turbulent combustion

Acknowledgements

This paper corresponds to an invited lecture given during the First Workshop on Quality Assessment of Unsteady Methods for Turbulent Combustion Prediction and Validation, Seeheim-Jugenheim, Germany, June 16–17 2005. D. Veynante gracefully acknowledges the organisers, Profs. J. Janicka and A. Sadiki, for this kind invitation.