Stationary Crossflow Breakdown Due to Interaction between Secondary Instabilities


Numerical simulations are used to continue an ongoing study of the laminar breakdown characteristics associated with stationary crossflow instability in the boundary-layer flow over a subsonic swept-wing configuration. The initial phase of this study had focused on the generic features of breakdown initiated by individual, fundamental modes of a given type of secondary instability waves. Follow-on work examined the role of more complex, yet controlled, spectra of the secondary instability modes by addressing a mixed mode transition scenario involving the simultaneous presence of Y and Z modes of secondary instability that are respectively associated with energy production mechanisms based on wall-normal and spanwise shear of the underlying basic state. For the initial amplitudes investigated in that work, the Y modes were found to play an insignificant role during the onset of transition in spite of achieving rather large, 0(5%), amplitudes of RMS velocity fluctuation prior to transition. This rather surprising finding was attributed to the fact that the Y modes are concentrated near the top of the crossflow vortex, and hence, 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. The present paper shows that suitable combinations of initial amplitudes of the Y and Z modes can lead to an additional breakdown scenario characterized by the rapid amplification of a mode that is generated by the interaction between the Y and Z modes and has a lower frequency equal to the difference of the Y- and Z-mode frequencies.

Meeting Name

47th AIAA Fluid Dynamics Conference, 2017 (2017: Jun. 5-9, Denver, CO)


Mechanical and Aerospace Engineering

Keywords and Phrases

Boundary layer flow; Fluid dynamics; Laminar boundary layer; Swept wings; Vortex flow, Breakdown characteristics; Cross-flow instabilities; Crossflow vortices; Energy productions; Fundamental modes; Lower frequencies; Secondary instability; Wing configurations, Stability

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Article - Conference proceedings

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