Low-frequency dynamics in a shock-induced separated flow

The low-frequency unsteadiness in the direct numerical simulation of a Mach 2.9 shock wave/turbulent boundary layer interaction with mean flow separation is analysed using dynamic mode decomposition (DMD). The analysis is applied both to three-dimensional and spanwise-averaged snapshots of the flow....

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Bibliographic Details
Published in:Journal of fluid mechanics 2016-11, Vol.807, p.441-477
Main Authors: Priebe, Stephan, Tu, Jonathan H., Rowley, Clarence W., Martín, M. Pino
Format: Article
Language:English
Subjects:
Boundary layer
Boundary layers
Flow separation
Fluid dynamics
Fluid mechanics
Shock waves
Turbulent flow
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Summary:The low-frequency unsteadiness in the direct numerical simulation of a Mach 2.9 shock wave/turbulent boundary layer interaction with mean flow separation is analysed using dynamic mode decomposition (DMD). The analysis is applied both to three-dimensional and spanwise-averaged snapshots of the flow. The observed low-frequency DMD modes all share a common structure, characterized by perturbations along the shock, together with streamwise-elongated regions of low and high momentum that originate at the shock foot and extend into the downstream flow. A linear superposition of these modes, with dynamics governed by their corresponding DMD eigenvalues, accurately captures the unsteadiness of the shock. In addition, DMD analysis shows that the downstream regions of low and high momentum are unsteady and that their unsteadiness is linked to the unsteadiness of the shock. The observed flow structures in the downstream flow are reminiscent of Görtler-like vortices that are present in this type of flow due to an underlying centrifugal instability, suggesting a possible physical mechanism for the low-frequency unsteadiness in shock wave/turbulent boundary layer interactions.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2016.557