Spatio-temporal dynamics of turbulent separation bubbles
Wen Wu, Charles Meneveau, and Rajat Mittal

TL;DR
This study investigates the complex spatio-temporal behavior of turbulent separation bubbles over a flat plate using direct numerical simulations, revealing distinct high- and low-frequency modes and their underlying mechanisms.
Contribution
It provides new insights into the dynamics of separation bubbles, especially the low-frequency breathing mode and the potential Görtler instability influence.
Findings
Identification of high-frequency vortex shedding mode.
Observation of a low-frequency breathing mode.
Evidence suggesting Görtler instability as a driving mechanism.
Abstract
The spatio-temporal dynamics of separation bubbles induced to form in a fully-developed turbulent boundary layer (with Reynolds number based on momentum thickness of the boundary layer of 490) over a flat plate are studied via direct numerical simulations. Two different separation bubbles are examined: one induced by a suction-blowing velocity profile on the top boundary and the other, by a suction-only velocity profile. The latter condition allows reattachment to occur without an externally imposed favourable pressure gradient and leads to a separation bubble more representative of those occurring over airfoils and in diffusers. The suction-only separation bubble exhibits a range of clearly distinguishable modes including a high-frequency mode and a low-frequency "breathing" mode that has been observed in some previous experiments. The high-frequency mode is well characterized by…
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