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A study on boundary-layer transition induced by free-stream turbulence

  • A. C. MANDAL (a1), L. VENKATAKRISHNAN (a2) and J. DEY (a1)
Abstract

Boundary-layer transition at different free-stream turbulence levels has been investigated using the particle-image velocimetry technique. The measurements show organized positive and negative fluctuations of the streamwise fluctuating velocity component, which resemble the forward and backward jet-like structures reported in the direct numerical simulation of bypass transition. These fluctuations are associated with unsteady streaky structures. Large inclined high shear-layer regions are also observed and the organized negative fluctuations are found to appear consistently with these inclined shear layers, along with highly inflectional instantaneous streamwise velocity profiles. These inflectional velocity profiles are similar to those in the ribbon-induced boundary-layer transition. An oscillating-inclined shear layer appears to be the turbulent spot-precursor. The measurements also enabled to compare the actual turbulent spot in bypass transition with the simulated one. A proper orthogonal decomposition analysis of the fluctuating velocity field is carried out. The dominant flow structures of the organized positive and negative fluctuations are captured by the first few eigenfunction modes carrying most of the fluctuating energy. The similarity in the dominant eigenfunctions at different Reynolds numbers suggests that the flow prevails its structural identity even in intermittent flows. This analysis also indicates the possibility of the existence of a spatio-temporal symmetry associated with a travelling wave in the flow.

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Email address for correspondence: jd@aero.iisc.ernet.in
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This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

P. Holmes , J. L. Lumley & G. Berkooz 1996 Turbulence, Coherent Structures, Dynamical Systems and Symmetry. Cambridge University Press.

M. V. Morkovin 1969 The many faces of transition. In Viscous Drag Reduction (ed. C. S. Wells ), pp. 131. Plenum Press.

M. Nishioka , M. Asai & S. Iida 1981 Wall phenomena in the final stage of transition to turbulence. In Transition and Turbulence (ed. R. E. Meyer ), pp. 113126. Academic Press.

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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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