Dynamics of turbulent separation bubbles – a linear modeling approach

• Applicants: Professor Dr.-Ing. Kilian Oberleithner; Professor Dr.-Ing. Julien Weiss
• Subject Area: Fluid Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504349109

The proposed research aims at the clarification of the driving mechanism(s) of low- and medium-frequency unsteadiness exhibited in low-speed turbulent separation bubbles (TSBs). Such unsteadiness is known to be detrimental to a variety of industrial flows through the generation of noise, vibration, or unsteady loads. Despite several decades of research, the exact mechanism associated with the low- and medium frequency dynamics of TSBs remains essentially unknown.In the proposed research, a novel linear approach to elucidate the low- and medium-frequency unsteadiness of TSBs will be adopted. Specifically, global linear stability analysis (GLSA) and resolvent analysis (RA) will be performed on a combined experimental (EFD) and computational fluid dynamics (CFD) database. The experiments will be carried out on TSBs generated in an asymmetric diffuser flow and will be complemented by large-eddy simulations (LES). GLSA and RA will be performed on the experimental and numerical mean flows with the aim of answering several research questions, notably whether the low-frequency breathing of the TSB is driven by absolute instability and whether the medium-frequency shedding occurs due to convective instability. A novel data assimilation scheme will also be implemented to circumvent the inconsistency of turbulence models occurring when linearized methods are applied to turbulent flows. Finally, based on the results of GLSA and RA, a control strategy will be devised and implemented in the wind tunnel to eliminate the low-frequency unsteadiness.This project combines the expertise in experimental aerodynamics of the Chair of Aerodynamics at TU Berlin (PI Weiss) with the expertise in LES, GLSA, and RA methods developed at the Laboratory for Flow Instabilities and Dynamics, also at TU Berlin (PI Oberleithner).

• DFG Programme: Research Grants