Performance Assessment of Modeling Approaches for Moderate or Intense Low-Oxygen Dilution Combustion in a Scale-Bridging Burner

The present work provides deep insights into methaneoxidationin a cyclonic flow field chamber whose strong internal recirculationof burnt products enables the attainment of a moderate or intenselow-oxygen dilution (MILD) combustion regime over a wide range ofoperating conditions. Steady-state Favre-averaged Navier-Stokes(FANS) simulations are performed to evaluate the thermochemical processestaking place within the reactor and to assess the suitability of existingcomputational fluid dynamics (CFD) models to describe the turbulence-chemistryinteractions in such a scale-bridging configuration. A sensitivityanalysis is carried out with respect to different turbulence closuremodels [i.e., renormalization group (RNG) k-& epsilon;,realizable k-& epsilon;, and Reynolds stressmodel], kinetic mechanisms (i.e., KEE-58 and GRI-Mech 2.11), as wellas different turbulent combustion approaches, i.e., the flamelet generatedmanifold (FGM), the eddy dissipation concept (EDC), and the partiallystirred reactor (PaSR) models. The accuracy of numerical predictionsis assessed by a direct comparison to obtained experimental resultsin terms of temperature profiles locally collected within the reactorand flue gas compositions monitored at the exit of the burner. Resultshighlight that the EDC and PaSR methods are the most suitable modelingparadigms for the investigated MILD combustion conditions, althoughthe former may likely predict an extinction of the combustion process;conversely, the FGM model shows the largest discrepancies with respectto experimental data, highlighting the need for improvements.