Dynamic Mode Decomposition of Turbulent Combustion Process in DLR Scramjet Combustor

Large eddy simulations (LES) are employed to investigate instabilities in the combustion process of a model scramjet combustor at the German Aerospace Center (DLR). Dynamic mode decomposition (DMD) is applied to analyze the numerical results. The DMD spectrum of the hydroxyl (OH) field is analyzed, and primary peaks are observed at 6375, 9763, 12063, and 15745 Hz, corresponding to S-t = 0.0524, 0.0802, 0.099, and 0.129, respectively. The DMD mode corresponding to S-t = 0.099 exhibits antisymmetric patterns in the wake of the strut, with the DMD mode corresponding to S-t = 0.129 displaying similar structures. The DMD spectrum of the hydroperoxyl (HO2) field is also investigated. Antisymmetric patterns initiating from both trailing edges of the strut are also extracted at nearly the same Strouhal numbers. DMD analyses are also performed on the pressure and velocity fields. The dominant frequencies in the pressure field are lower than those of the OH and HO2 fields, indicating that the dominant pressure oscillation is unlikely to couple with the strongest unsteadiness in the OH and HO2 fields. The streamwise component of the velocity DMD mode attributed to the same Strouhal number exhibits an antisymmetric pattern similar to the most unstable OH DMD modes. Wake instability is believed to be the main cause of the dominant oscillations in the OH field. Moreover, the unsteady characteristics of the HO2 field are also related to the wake instability. (C) 2017 American Society of Civil Engineers.