A Unified Thickened Flame-Fine-Scales Framework for Multi-Regime Combustion Modelling: Application to an Industrial Lean-Premixed Burner

Abstract

In the pursuit of net-zero energy systems, advanced combustion concepts are essential to ensure safe and efficient operation of future gas turbines (GTs) across sustainable fuels and carbon-neutral solutions. Under such unconventional conditions, flames no longer conform to a single regime but span from premixed to non-premixed combustion, depending on fuel injection strategy, turbulence intensity, and local flow field.

While scale-resolving reactive Computational Fluid Dynamics (CFD) is central to GT design, modelling multi-regime combustion remains challenging, as most models are tailored to single regimes, limiting accurate prediction of flame stabilisation and emissions. Furthermore, the high Reynolds numbers typical of industrial burners demand accurate treatment of turbulence-chemistry interaction (TCI) to resolve flame dynamics.

In Large-Eddy Simulations (LES) based on species transport models, a flame index is employed to identify local regimes, with the Thickened Flame (TF) model applied to premixed combustion. In non-premixed regions, however, thickening is typically deactivated, leaving TCI unresolved and leading to inaccuracies at practical grid resolutions.

To address these limitations, this study presents a unified Thickened Flame-Fine-Scales (TF-FS) formalism, coupling the Dynamic Thickened Flame model (DTFLES) with a fine-scales-based TCI closure. Premixed combustion is handled by DTFLES, while non-premixed regions are modelled using an LES-adapted formulation of the Eddy Dissipation Concept (EDC).

The hybrid approach, previously assessed on academic configurations, is applied here to a full-scale industrial lean-premixed burner and evaluated against experimental data from the THT Lab in Florence.