Deterministic Multiple Mapping Conditioning (MMC) applied to a turbulent flame in Large Eddy Simulation (LES)

Abstract

The scalar dissipation rate is a key quantity in turbulent combustion modelling, in particular for Conditional Moment Closure (CMC). In Large Eddy Simulation (LES), a subgrid-scale (SGS) mixing model must be provided to determine the SGS mixture fraction variance needed for the filtered scalar dissipation rate and the filtered density function. Multiple Mapping Conditioning (MMC) is selected as a SGS mixing model and the deterministic form is implemented for the first time in LES. The objective of the present study is to assess the capabilities of MMC to model the turbulent mixing field and the conditionally filtered scalar dissipation rate, N|η∼ needed in CMC.The MMC transport equation is implemented in a LES code coupled with CMC to simulate a lifted jet flame in a vitiated coflow. The MMC formulation and computational details are presented. MMC predictions are compared with LES for the turbulent mixing field using instantaneous and time averaged data, and experimental values are included whenever available.Reasonable agreement between MMC, LES and experimental data is found. Best fit is obtained close to the fuel exit and some discrepancies can be seen further downstream. The SGS variance is underpredicted for many parts of the jet. A thorough analysis is performed to assess the modelling and numerical assumptions. The two proposed sources of discrepancy are the linear model and neglect of a transverse component for convection in MMC. The MMC profiles of N|η∼ are significantly different from those of AMC and are sensitive to the SGS variance. Future work is suggested.