Assessment of a Hybrid LES-CAA Method for Predicting Flame Responses in Swirl-Stabilized Combustion Under Various Acoustic Excitations

Thermoacoustic instabilities present a significant challenge in modern combustion systems due to the complex and potentially harmful interactions between unsteady heat release, acoustics, and flow dynamics. In this study, a hybrid Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA) method is applied to evaluate the flame response of a well-known academic combustor configuration. The method combines CFD for simulating flow and combustion with CAA for simulating acoustic wave propagation, effectively separating distinct physical domains, allowing for the use of tailored numerics. The established BRS configuration offers validation data and serves as a benchmark for evaluating flame response predictions, thereby helping to advance the hybrid method. To that end, the flame response is assessed through the Flame Transfer Function (FTF), which quantifies the relationship between acoustic perturbations and unsteady heat release, enabling a direct comparison with experimental and reference data. This work employs two distinct acoustic excitation signals in the CAA domain: a broadband and a multi-sine excitation signal. The acoustic results are post-processed and compared between the excitation signals, using both a direct evaluation of the FTF and a System Identification approach, further comparing the findings to experimental data. The results emphasize the critical role of properly constructing and applying excitation signal boundary conditions for reliable acoustic characterization in this framework.