Print Email Facebook Twitter Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step Title Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step Author Hu, W. (TU Delft Aerodynamics) Hickel, S. (TU Delft Aerodynamics) van Oudheusden, B.W. (TU Delft Aerodynamics) Date 2021 Abstract The low-frequency unsteady motions behind a backward-facing step (BFS) in a turbulent flow at and are investigated using a well-resolved large-eddy simulation. The instantaneous flow field illustrates the unsteady phenomena of the shock wave/boundary layer interaction (SWBLI) system, including vortex shedding in the shear layer, the flapping motions of the shock and breathing of the separation bubble, streamwise streaks near the wall and arc-shaped vortices in the turbulent boundary layer downstream of the separation bubble. A spectral analysis reveals that the low-frequency behaviour of the system is related to the interaction between shock wave and separated shear layer, while the medium-frequency motions are associated with the shedding of shear layer vortices. Using a three-dimensional dynamic mode decomposition (DMD), we analyse the individual contributions of selected modes to the unsteadiness of the shock and streamwise-elongated vortices around the reattachment region. Görtler-like vortices, which are induced by the centrifugal forces originating from the strong curvature of the streamlines in the reattachment region, are strongly correlated with the low-frequency unsteadiness in the current BFS case. Our DMD analysis and the comparison with an identical but laminar case provide evidence that these unsteady Görtler-like vortices are affected by fluctuations in the incoming boundary layer. Compared with SWBLI in flat plate and ramp configurations, we observe a slightly higher non-dimensional frequency (based on the separation length) of the low-frequency mode. Subject compressible boundary layersshock waveswave-turbulence interactions To reference this document use: http://resolver.tudelft.nl/uuid:5ac7ca37-f7ff-4d10-8a8c-73ea84ac76f9 DOI https://doi.org/10.1017/jfm.2021.95 ISSN 0022-1120 Source Journal of Fluid Mechanics, 915 Part of collection Institutional Repository Document type journal article Rights © 2021 W. Hu, S. Hickel, B.W. van Oudheusden Files PDF low_frequency_unsteadines ... g_step.pdf 13.2 MB Close viewer /islandora/object/uuid:5ac7ca37-f7ff-4d10-8a8c-73ea84ac76f9/datastream/OBJ/view