The effect of combustion sub-grid closures in LES of MILD combustion

In Moderate or Intense Low oxygen Dilution (MILD) combustion regime, the system evolves towards a distributed reaction regime and low temperatures, which leads to higher chemical and lower mixing time scales. Thus, the characteristic Damk¨ohler number has the order of 1. As a result, models accounting for finite rate chemistry should be considered. In the present work, the Partially Stirred Reactor (PaSR) model is used. In PaSR, the influence of the sub-grid fluctuations on the reaction rate is expressed with a factor k. Recently, it was shown that k approaches 1.0 in MILD combustion, suggesting that reacting structures can be resolved on the Large Eddy Simulation (LES) grid using implicit models in which the turbulent effect is not directly included.