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On the role of the outer region in the turbulent-boundary-layer bursting process

Published online by Cambridge University Press:  26 April 2006

ROY Y. Myose
Affiliation:
Department of Aerospace Engineering, University of Southern California, Los Angeles, CA 90089-1191, USA Present address: Department of Aerospace Engineering, Wichita State University, Wichita, KS 67260-0044, USA.
Ron F. Blackwelder
Affiliation:
Department of Aerospace Engineering, University of Southern California, Los Angeles, CA 90089-1191, USA

Abstract

The dynamics and interaction of turbulent-boundary-layer eddy structures was experimentally emulated. Counter-rotating streamwise vortices and low-speed streaks emulating turbulent-boundary-layer wall eddies were generated by a Görtler instability mechanism. Large-scale motions associated with the outer region of turbulent boundary layer were emulated with — ωz spanwise vortical eddies shed by a periodic non-sinusoidal oscillation of an airfoil. The scales of the resulting eddy structures were comparable to a moderate-Reynolds-number turbulent boundary layer. Results show that the emulated wall-eddy breakdown was triggered by streamwise acceleration associated with the outer region of turbulent boundary layer. This breakdown involved violent mixing between low-speed fluid from the wall eddy and accelerated fluid associated with the outer structure. Although wall eddies can break down autonomously, the presence of and interaction with outer-region — ωz eddies hastened their breakdown. Increasing the — ωz eddy strength resulted in further hastening of the breakdown. Conversely, + ωz eddies were found to delay wall-eddy breakdown locally, with further delays resulting from stronger + ωz eddies. This suggests that the outer region of turbulent boundary layers plays a role in the bursting process.

Type
Research Article
Copyright
© 1994 Cambridge University Press

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