Session: 04-09 Combustion Dynamics III

Submission Number: 177075

Flame Dynamics Similarity in a Geometrically Scaled Lean-Premixed Swirl Combustor 

Understanding how the flame response scales with geometric and flow parameters is essential for transferring combustion stability characteristics between combustors of different sizes. While scaling laws for non-reactive flow fields are well established, the corresponding relationships for thermoacoustic systems remain poorly understood. This study investigates how the flame response of a lean premixed swirl combustor varies under different geometric and flow scaling criteria. A series of reactive Large Eddy Simulations (LES) is conducted for the lean premixed swirl burner, employing geometrical scaling ratios for up- and downscaling, respectively. For each geometry, the inlet velocity is adjusted to preserve either the Damköhler number (Da), the Reynolds number (Re), or the reference velocity. The resulting datasets are analysed to determine both mean flow and mean flame properties. Subsequently, System Identification (SI) techniques are applied to extract the flame response to acoustic perturbations in terms of Flame Transfer Functions (FTFs). The simulations reveal pronounced differences in flame length and dynamics between the scaling criteria. Only if the inlet velocity is scaled to maintain a constant Damköhler number Da does the flame length vary proportionally with the applied geometric scaling factor. In the thermoacoustic domain, a Strouhal-based normalization collapses the phase behaviour of all cases, indicating a consistent temporal scaling. Furthermore, the gain curves of the FTFs exhibit self-similar behaviour exclusively under Da-scaled conditions. These findings demonstrate that reliable and robust scaling of the flame response in a geometrically scaled swirl-stabilized combustor requires velocity adjustments that preserve the Damköhler number. The results thus provide a physically consistent basis for scaling combustor stability characteristics.

Presenting Author: Korbinian Niebler Technical University of Munich

Presenting Author Biography: Korbinian Niebler is a PhD student in the Thermo-Fluid Dynamics Group of Prof. Wolfgang Polifke at Technical University of Munich. He has specialized his research on the time domain perspective of thermoacoustic phenomena and scaling rules for flame responses.

Authors:

Korbinian Niebler Technical University of Munich
Matthias Reinert Technical University of Munich
Camilo F. Silva Technical University of Munich
Luis Tay-Wo-Chong Ansaldo Energia Switzerland AG
Wolfgang Polifke Technical University of Munich