Dynamics of turbulent separation bubbles – a linear modeling approach

本研究旨在阐明低速湍流分离泡（TSB）中低频非定常的驱动机制。 已知这种不稳定性通过产生噪声、振动或不稳定负载而对各种工业流有害。尽管经过几十年的研究，与中低频动力学的TSB的确切机制仍然基本上是未知的。在拟议的研究中，一个新的线性方法来阐明的中低频不稳定的TSB将采用。具体而言，将在综合实验（EFD）和计算流体动力学（CFD）数据库上进行全局线性稳定性分析（GLSA）和预解式分析（RA）。实验将在非对称扩压器流中产生的TSB上进行，并将通过大涡模拟（LES）进行补充。GLSA和RA将在实验和数值平均流上进行，目的是回答几个研究问题，特别是TSB的低频呼吸是否由绝对不稳定性驱动，以及中频脱落是否由于对流不稳定性而发生。一个新的数据同化方案也将实施，以规避不一致的湍流模型时发生的线性化方法应用于湍流。最后，基于GLSA和RA的结果，将设计并在风洞中实施控制策略以消除低频不稳定性。该项目结合了柏林工业大学空气动力学主席（PI韦斯）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).