Interaction of second-mode disturbances with an incipiently separated compression-corner flow. (4th March 2021)

• Record Type: Journal Article
• Authors: Butler, Cameron S.; Laurence, Stuart J.
• Is Part Of: Journal of fluid mechanics. Volume 913(2021)
• Publication Date: 2021-03-04
• Subjects: high-speed flow, -- boundary layer stability, -- compressible boundary layers; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2021.91
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: 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.