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Nonlinear global instability in buoyancy-driven boundary-layer flows

Published online by Cambridge University Press:  05 October 2006

J. TAO
J. TAO
Affiliation:
Institute of Physics, Bayreuth University, Bayreuth 95440, Germany LTCS and Department of Mechanics and Engineering Science, Peking University, Beijing 100871, China
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Abstract

Direct numerical simulation (DNS) and a linear analysis of the global instability of a buoyancy layer have been performed. The spatially developing basic flow under consideration is induced by a vertical heated flat plate immersed in a thermally stratified medium. It is revealed numerically that, depending on the modified Grashof number, the disturbed flat-plate boundary-layer flows may not relax to the basic state but instead oscillate with an intrinsic frequency. The front of globally unstable waves in numerical simulations agrees very well with the position of marginal absolute instability, and the dominant frequencies in the oscillating region are identical and tuned to the marginal absolute frequency derived from the local linear dispersion relation based on the unperturbed basic state. The front of the nonlinear global modes is thus of a pulled type in this buoyancy-driven flow system.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 566 , 10 November 2006 , pp. 377 - 388
Copyright
© 2006 Cambridge University Press

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