Conditional Moment Closure Methods for Turbulent Non-premixed Combustion

Abstract

Computational models for engineering applications need to be both accurate and computationally efficient. Turbulent flows with combustion cannot be directly solved due to the wide range of spatial scales and the large number of reactive scalars. In non-premixed systems, strong correlations exist between the value reactive scalar and the mixing between the fuel and oxidiser. Conditional moment closure (CMC) methods assumed that conditional fluctuations around a single scalar (in non-premixed flows the mixture fraction) are small. Using this assumption, CMC models derive Eulerian transport equations for the conditioned scalars that can be solved efficiently. This chapter will introduce the CMC method in non-premixed combustion and its formulations in RANS and LES, with the modelling of the unclosed terms and relevant algorithms. Next, the chapter will review recent progress in CMC modelling of auto-ignition, flame stabilisation and extinction; including recent applications in engines and gas turbine combustion, as well as theoretical developments on double conditioning, differential diffusion and spray combustion.