Mixing Time Scale Models for Multiple Mapping Conditioning with Two Reference Variables

Abstract

A novel multiple mapping conditioning (MMC) approach has been developed for the modelling of turbulent premixed flames including mixture inhomogeneities due to mixture stratification or mixing with the cold surroundings. MMC requires conditioning of a mixing operator on characteristic quantities (reference variables) to ensure localness of mixing in composition space. Previous MMC used the LES-filtered reaction progress variable as reference field. Here, the reference variable space is extended by adding the LES-filtered mixture fraction effectively leading to a double conditioning of the mixing operator. The model is used to predict a turbulent stratified flame and is validated by comparison with experimental data. The introduction of the second reference variable also requires modification of the mixing time scale. Two different mixing time scale models are compared in this work. A novel anisotropic model for stratified combustion leads to somewhat higher levels of fluctuations for the passive scalar when compared with the original model but differences remain small within the flame front. The results show that both models predict flame position and flame structure with good accuracy.

Numerical Investigation of Different Combustion Models for Dual‐Fuel Engine Combustion Processes

“…In diesel engines a significant part of combustion is thought to be mixing-controlled. Hence, interactions between turbulence and chemical reactions have to be considered [17]. The model described in this section combines a laminar and a turbulent timescale to an overall reaction rate [15].…”