Stationary Crossflow Breakdown Due to Mixed Mode Spectra of Secondary Instabilities


Numerical simulations are used to study laminar breakdown characteristics associated with stationary crossflow instability in the boundary-layer flow over a subsonic swept-wing configuration. Previous work involving the linear and nonlinear development of individual, fundamental modes of secondary instability waves is extended by considering the role of more complex, yet controlled, spectra of the secondary instability modes. Direct numerical simulations target a mixed mode transition scenario involving the simultaneous presence of Y and Z modes of secondary instability. For the initial amplitudes investigated in this paper, the Y modes are found to play an insignificant role during the onset of transition, in spite of achieving rather large, O(50/o), amplitudes of RMS velocity fluctuation prior to transition. Analysis of the numerical simulations shows that this rather surprising finding can be attributed to the fact that the Y modes are concentrated near the top of the crossflow vortex and exert relatively small influence on the Z modes that reside closer to the surface and can lead to transition via nonlinear spreading that does not involve interactions with the Y mode. Finally, secondary instability calculations reveal that subharmonic modes of secondary instability have substantially low er growth rates than those of the fundamental modes, and hence, are less likely to play an important role during the breakdown process involving complex initial spectra.

Meeting Name

46th AIAA Fluid Dynamics Conference (2016: Jun. 13-17, Washington, DC)


Mechanical and Aerospace Engineering

Research Center/Lab(s)

Center for High Performance Computing Research

Keywords and Phrases

Boundary Layer Flow; Boundary Layers; Fluid Dynamics; Laminar Boundary Layer; Numerical Models; Swept Wings; Vortex Flow; Breakdown Characteristics; Breakdown Process; Cross-Flow Instabilities; Crossflow Vortices; Fundamental Modes; Secondary Instability; Subharmonic Modes; Wing Configurations; Stability

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


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© 2016 American Institute of Aeronautics and Astronautics (AIAA), All rights reserved.

Publication Date

01 Jun 2016

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