Large-Eddy Simulation of Lean Premixed Flames in a Model Swirl Burner

Lean premixed flames in an un-confined model swirl burner are studied numerically by means of large eddy simulation. In the burner considered, swirling flow and a richer pilot flame are used to stabilize the flame. The paper investigates the occurrence of the central recirculation zone (CRZ) and the precessing vortex core (PVC) for two variants of the burner, as well as the flame response to a sinusoidal variation of the mass flow rate in the pilot jet. The corresponding isothermal swirling flows are also simulated for providing reference. Detailed comparisons with experimental data are performed for velocity statistics and generally good agreement is achieved. Additionally, coherent structures are analyzed and local power spectra computed. It is found that a very strong PVC is observed in numerical results and experiment for the non-reactive case with retracted pilot jet. In the reactive cases where the whole CRZ is enclosed in the high-temperature post-flame region, the PVC is almost completely suppressed.