The coupling between scales in shear flows

Promode R. Bandyopadhyay, A. K.M.F. Hussain

Research output: Contribution to journalArticlepeer-review

105 Scopus citations

Abstract

In order to explore the relationship between the large- and small-scale motions in turbulent shear flows, a number of flows have been studied based on short-time correlation measurements. The shear flows investigated are boundary layers, plane and axisymmetric mixing layers, plane wakes and the far fields of plane and circular jets. The coupling between the scales has been obtained by correlating the low-frequency component of the u-velocity signal with a signal that is similar to the envelope of the high-frequency part of the velocity signal. The coupling is found to be significant in all flows. Phase reversal across the shear region is found to occur in the boundary layers and the mixing layers only. This is interpreted to mean that in boundary layers and mixing layers, the stream wise extent of the large structure over which the small-scale activity reaches a peak moves at one transverse end of the large structure over which its ensemble averaged u fluctuation is positive to another where it is negative. This phase shift (≃180°) of the location of the peak activity of the small scales with respect to the large structure takes place gradually resulting in a midlayer where the phase difference is about 90°. On the other hand, in the far field of the jets and wakes, all across the layer, the peak activity of the small scales always remains confined to that half of the streamwise extent of the large structure where its ensemble averaged u fluctuation is positive; in the remaining streamwise half of the large structure, the small scales remain dormant.

Original languageEnglish
Pages (from-to)2221-2228
Number of pages8
JournalPhysics of Fluids
Volume27
Issue number9
DOIs
StatePublished - 1984

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