Dynamics of turbulent separation bubbles – a linear modeling approach

本研究旨在阐明低速湍流分离气泡（TSBs）中低频非定常的驱动机理。众所周知，这种不稳定性通过产生噪声、振动或非定常负载而对各种工业流动有害。尽管经过几十年的研究，与tsb的低频和中频动力学相关的确切机制仍然基本上是未知的。在本研究中，将采用一种新颖的线性方法来解释tsb的低频和中频不稳定性。具体来说，全球线性稳定性分析（GLSA）和解决方案分析（RA）将在联合实验（EFD）和计算流体动力学（CFD）数据库上进行。实验将在不对称扩散流中产生的tsb上进行，并将辅以大涡模拟（LES）。GLSA和RA将在实验和数值平均流上进行，旨在回答几个研究问题，特别是TSB的低频呼吸是否由绝对不稳定驱动，中频脱落是否由对流不稳定引起。一种新的数据同化方案也将被实施，以避免当线性化方法应用于湍流时出现的湍流模型不一致。最后，基于GLSA和RA的结果，设计并实施了风洞控制策略，以消除低频失稳。该项目结合了柏林工业大学空气动力学主席（PI Weiss）在实验空气动力学方面的专业知识，以及柏林工业大学流动不稳定性和动力学实验室（PI Oberleithner）在LES、GLSA和RA方法方面的专业知识。

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).