A modal decomposition-based partially stirred reactor (mPaSR) model for turbulent combustion closure: Implementation details and a posteriori validation

This paper investigates a turbulence-chemistry interaction model based on the Partially Stirred Reactor (PaSR) paradigm where the hypothesis of relying on an individual chemical timescale is relaxed to deal with multiscale problems. The modal Partially Stirred Reactor (mPaSR) model relies on the Computational Singular Perturbation (CSP) theory and performs an eigen-decomposition of the Jacobian matrix of the chemical source terms. The CSP manifold is then corrected by modal fractions that, similarly to the cell reacting fraction of the original PaSR model, account for the individual mode timescales. The vector of the chemical source terms, to be returned to the computational fluid dynamics solver, acts as an aggregated contribution of the corrected CSP modes. The predictive capabilities of the mPaSR model are demonstrated a posteriori through a series of Unsteady Reynolds-Averaged Navier–Stokes simulations of the well-documented Sandia flames. Promising results are observed at different turbulence levels making the mPaSR approach a valuable alternative to existing turbulence-chemistry interaction models. Particular attention is given to the formation of pollutants, and accurate predictions of nitric oxide NO are obtained. Novelty and significance statement The novelty of this work lies in the code development, integration and a posteriori testing of an innovative combustion model accounting for several timescales of dynamical chemical systems. This represents an important step towards well-suited approaches for the modelling of multiscale processes such as pollutant formation in turbulent flames. The model shows promising prediction capabilities with desirable computational efficiency on the investigated cases, motivating follow-up investigations in a larger range of combustion scenarios.