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Phase-averaged measurements of perturbations introduced into boundary layersLarge-scale structures in turbulent and transitional wall-bounded flows make a significant contribution to the Reynolds stress and turbulent energy. The behavior of these structures is examined. Small perturbations are introduced into a laminar and a turbulent boundary layer to trigger the formation of large-scale features. Both flows use the same inlet unit Reynolds number, and they experience the same pressure gradient history, i.e. a favorable pressure gradient (FPG) followed by an adverse pressure gradient (APG). The perturbation consists of a small short duration flow repetitively introduced through a hole in the wall located at the C(sub p) minimum. Hot-wire data are averaged on the basis of the phase of the disturbance, and automation of the experiment was used to obtain measurements on large spatially dense grids. In the turbulent boundary, the perturbation evolves into a vortex loop which retains its identity for a considerable streamwise distance. In the laminar layer, the perturbation decays to a very small magnitude before growing rapidly and triggering the transition process in the APG. The 'time-like' animations of the phase-averaged data are used to gain insight into the naturally occurring physical mechanisms in each flow.
Document ID
19930073997
Acquisition Source
Legacy CDMS
Document Type
Other
Authors
Watmuff, Jonathan H.
(Stanford Univ. CA, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1991
Publication Information
Publication: Annual Research Briefs, 1990
Subject Category
Fluid Mechanics And Heat Transfer
Accession Number
93N71444
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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