Hypersonic boundary-layer flows over a circular cone at a moderate yaw angle can support strong crossflow instability away from the windward and leeward rays on the plane of symmetry. Due to the more efficient excitation of stationary crossflow vortices by surface roughness, a possible path to transition in such flows corresponds to rapid amplification of the high-frequency instabilities sustained in the presence of finite amplitude stationary crossflow vortices. This paper presents a computational analysis of crossflow instability over a 7-degree half-angle, yawed circular cone in a Mach 6 free stream. Specifically, the nonlinear evolution of an azimuthally localized crossflow vortex pattern and the linear amplification characteristics of high-frequency instabilities evolving in the presence of that pattern are described for the first time. Focusing on the azimuthally compact vortex pattern allows us to overcome significant limitations of the prior secondary instability analyses of azimuthally inhomogeneous boundary layer flows. A comparison between plane-marching parabolized stability equations and direct numerical simulations (DNS) reveals favorable agreement in regard to mode shapes, most amplified disturbance frequencies, and the N-factor evolution. In contrast, the Quasi parallel predictions are found to result in a severe underprediction of the N-factors. The most amplified high-frequency instabilities are found to originate from Mack's second mode waves sustained within the upstream region of nearly unperturbed, quasi-homogeneous boundary layer.


Mechanical and Aerospace Engineering


National Aeronautics and Space Administration, Grant None

Keywords and Phrases

Crossflow instability; Hypersonic boundary layers; Laminar-turbulent transition; Second mode instability; Secondary instability; Yawed cone

International Standard Serial Number (ISSN)

1432-2250; 0935-4964

Document Type

Article - Journal

Document Version


File Type





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Publication Date

01 Apr 2022