Large eddy simulation of multi-regime turbulent combustion with modal partially stirred reactor models

Turbulent reacting flows are described as multi-scale processes with characteristic flow and chemical timescales spanning several orders of magnitude. Species source term closure models that rely on the description of such systems through a single scale make a strong assumption, failing to provide accurate estimations for chemical processes with significantly different characteristic timescales. The modal Partially Stirred Reactor (mPaSR) model overcomes this limitation by accounting for all chemical system dynamics through the modal decomposition of the Jacobian matrix of the species source terms. Following a priori testing on direct numerical simulation data and simulations using the Reynolds-averaged Navier–Stokes approach, this work details the first mPaSR model assessment in the context of Large Eddy Simulation (LES). Model validation is achieved through a series of LES of the Darmstadt Multi-Regime Burner (MRB). Attention is paid to the quality of temperature and carbon monoxide estimations in comparison to the measurements. Insights into the model are provided by assessing the resulting flow fields with tools from the Computational Singular Perturbation (CSP) theory. The study supports the use of the mPaSR model for the numerical investigation of complex turbulent reacting flows with the LES approach. Novelty and significance The novelty of this work lies in the first a posteriori testing, in the context of Large Eddy Simulation, of an innovative combustion model accounting for several timescales of dynamical chemical systems. This represents an important step towards developing well-suited approaches for modelling multi-regime combustion and multi-scale processes, such as pollutant formation in turbulent flames. The model demonstrates promising predictive capabilities in the investigated cases, motivating further studies across a broader range of combustion scenarios.