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Interaction of second-mode disturbances with an incipiently separated compression-corner flow

Published online by Cambridge University Press:  04 March 2021

Cameron S. Butler  and
Stuart J. Laurence Open the ORCID record for Stuart J. Laurence [Opens in a new window]
Cameron S. Butler
Affiliation:
Department of Aerospace Engineering, University of Maryland–College Park, College Park, MD 20742, USA
Stuart J. Laurence*
Affiliation:
Department of Aerospace Engineering, University of Maryland–College Park, College Park, MD 20742, USA
*
†Email address for correspondence: stuartl@umd.edu
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Abstract

An experimental campaign was conducted to examine the impact of an abrupt change in surface geometry on hypersonic boundary-layer instability waves. The primary test configuration consisted of a $5^{\circ }$ half-angle, nominally sharp cone with a $15^{\circ }$ half-angle flare attachment. Tests were conducted at Mach 6 with the unit Reynolds number varying from $3.0\times 10^6$ to $4.9\times 10^6\ \textrm {m}^{-1}$. The $10^{\circ }$ compression was sufficient to create a small separation region at the cone–flare junction at these conditions. Ultra-high-speed schlieren (822 kHz) revealed the propagation of second-mode disturbances with frequencies between 200 and 300 kHz within the upstream boundary layer; when these reached the separation region, radiation of disturbance energy along the separation shock was observed. Tests conducted at low unit Reynolds numbers demonstrated inhibited instability growth (compared to the straight-cone case) through the separation region and the development of low-frequency (${\sim }75\ \textrm {kHz}$) instabilities within the separated shear layer. At higher Reynolds numbers, however, the corner interaction was found to cause rapid breakdown near reattachment, leading to earlier transition than for a straight cone. Analysis of the schlieren images using spectral proper orthogonal decomposition provided a global picture of the structure and development of the second-mode and shear-generated instabilities.

JFM classification

Aerodynamics: High-speed flow Boundary Layers: Boundary layer stability Compressible Flows: Compressible boundary layers

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JFM Rapids
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Journal of Fluid Mechanics , Volume 913 , 25 April 2021 , R4
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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References

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Butler and Laurence supplementary movie 1

Test-time image sequence for condition Re30: (Top) Raw images, (top-middle) reference-subtracted images, (bottom-middle) 175-275 kHz bandpass-filtered images and (bottom) 70-86 kHz bandpass-filtered images.

Download Butler and Laurence supplementary movie 1(Video)
Video 47 MB

Butler and Laurence supplementary movie 2

Test-time image sequence for condition Re42: (Top) Raw images, (top-middle) reference-subtracted images, (bottom-middle) 200-300 kHz bandpass-filtered images and (bottom) 76-92 kHz bandpass-filtered images.

Download Butler and Laurence supplementary movie 2(Video)
Video 49 MB

Butler and Laurence supplementary movie 3

Test-time image sequence for condition Re49: (Top) Raw images, (top-middle) reference-subtracted images, (bottom-middle) 225-325 kHz bandpass-filtered images and (bottom) 82-98 kHz bandpass-filtered images.

Download Butler and Laurence supplementary movie 3(Video)
Video 43.3 MB

Butler and Laurence supplementary movie 4

Average PSD computed for individual frequencies at (top) condition Re30, (middle) condition Re42 and (bottom) condition Re49.

Download Butler and Laurence supplementary movie 4(Video)
Video 4.1 MB