A priori testing of mixing models for Monte-Carlo PDF simulations

A priori testing of mixing models widely-used for Monte-Carlo PDF simulations, in particular the IEM, the modified Curl and the EMST models, has been performed, using the data obtained from the direct numerical simulations (DNS) specifically designed for the study of local flame extinction and re-ignition. The tests are designed to examine the model performance when implemented in both Reynolds-averaged simulations and large-eddy simulations. The exact value of the mixing frequency is taken from the DNS (i.e., not chosen to fit the data), so that the "true" model performance can be demonstrated. It is found that, in general, the EMST model yields much better results than the others. The performance of the new mixing model proposed by the authors - a new Lagrangian flamelet model- will also be presented. This new mixing model reasonably accounts for the difference between the mixing of passive and reactive scalars, while the presently available mixing models do not distinguish between them.