Hybrid Large Eddy Simulation of Flow and Flame Dynamics in a Single Flame Augmenter

This study numerically investigates the flame dynamics and thermoacoustic oscillations in a Single Flame Augmenter (SFA) setup – a bluffbody stabilized liquid fuel combustor operating with vitiated oxidizer flow (Mach = 0.34, 1100 K, and 15% oxygen) – using the hybrid Large Eddy Simulation (LES) approach. In this work, the hybrid LES approach is coupled with Lagrangian particle tracking for fuel spray modeling, and the turbulence–combustion interaction is modeled using the Partially Stirred Reactor (PaSR) approach. All simulations are performed in OpenFOAM. Simulations mimicking the experimental equivalence ratios of ϕ = 0.5, 0.7, and 1.0 capture the transition of flame topology from symmetric to asymmetric with an increase in equivalence ratio. At high ϕ, the Bénard – von Kármán oscillations dominate, whereas at lower ϕ, a more symmetric flame is obtained. Additionally, the results reproduce the high-frequency flame oscillations at ∼1200 Hz, with a potential to trigger thermoacoustic screech in a realistic afterburner. Further, at higher equivalence ratios (ϕ = 0.7 and 1), the simulations predict the excitation of the 3/4th longitudinal mode at 250 Hz, confirmed by the pressure probe spectra and the Dynamic Mode Decomposition (DMD) analysis. The results also capture oscillations in the spray stream, aligning with experimental observations. Additionally, these results demonstrate the capability of hybrid LES in adequately resolving the flame, flow, and spray interactions that are relevant to afterburner screech, providing a validated baseline for subsequent perturbation studies.