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Mechanisms of instability growth, interaction and breakdown induced by a backward-facing step in a swept-wing flow

Published online by Cambridge University Press:  18 November 2021

Jenna L. Eppink Open the ORCID record for Jenna L. Eppink [Opens in a new window]
Jenna L. Eppink*
Affiliation:
Flow Physics and Control Branch, NASA Langley Research Center, Hampton, VA23681, USA
*
†Email address for correspondence: jenna.eppink@nasa.gov
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Abstract

Time-resolved particle image velocimetry measurements were performed downstream of a swept backward-facing step. The measurements allow detailed analysis of the interactions between the unsteady instabilities and the stationary crossflow vortices. Different mechanisms are identified that lead to the modulation of the different families of unsteady instabilities that occur downstream of the step. For the low-frequency spanwise-travelling mode, the modulation occurs due to a redistribution of momentum when the instability encounters regions of large spanwise shear of the wall-normal and streamwise velocity. However, the higher-frequency streamwise-travelling instabilities undergo the familiar ‘lift-up’ mechanism when they encounter the regions of large vertical velocity due to the presence of the stationary crossflow vortices. The process leading to large velocity spikes, and ultimately to a laminar breakdown to turbulence, is identified as a constructive interaction between the different unsteady instabilities, coupled with an interaction with the stationary crossflow vortices when the phases align properly.

JFM classification

Boundary Layers: Boundary layer stability Instability: Transition to turbulence
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 931 , 25 January 2022 , A1
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Copyright
© National Aeronautics and Space Administration and The Author(s), 2021. To the extent this is a work of the US Government, it is not subject to copyright protection within the United States. Published by Cambridge University Press

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References

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