Streak instability in near-wall turbulence revisited

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Title: Streak instability in near-wall turbulence revisited
Authors: Cassinelli, A
De Giovanetti, M
Hwang, Y
Item Type: Journal Article
Abstract: The regeneration cycle of streaks and streamwise vortices plays a central role in the sustain- ment of near-wall turbulence. In particular, the streak breakdown phase in the regeneration cycle is the core process in the formation of the streamwise vortices, but its current under- standing is limited particularly in a real turbulent environment. This study is aimed at gaining fundamental insight into the underlying physical mechanism of the streak breakdown in the presence of background turbulent uctuation. We perform a numerical experiment based on direct numerical simulation, in which streaks are arti cially generated by a body forcing computed from previous linear theory. Upon increasing the forcing amplitude, the arti cially driven streaks are found to generate an intense uctuation of the wall-normal and spanwise velocities in a fairly large range of amplitudes. This cross-streamwise velocity uctuation shows its maximum at λ + x ≈ 20000 ( λ + x is the inner-scaled streamwise wavelength), but it only appears for λ + x ≤ 3000 - 4000. Further examination with dynamic mode decomposition reveals that the related ow eld is composed of sinuous meandering motion of the driven streaks and alternating cross-streamwise velocity structures, clearly reminiscent of sinuous- mode streak instability found in previous studies. Finally, it is shown that these structures are reasonably well aligned along the critical layer of the secondary instability, indicating that the surrounding turbulence does not signi cantly modify the inviscid in ectional mechanism of the streak breakdown via streak instability and/or streak transient growth.
Date of Acceptance: 9-Feb-2017
ISSN: 1468-5248
Publisher: Taylor & Francis
Journal / Book Title: Journal of Turbulence
Sponsor/Funder: Engineering and Physical Sciences Research Council
Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: EP/N019342/1
Keywords: Fluids & Plasmas
0915 Interdisciplinary Engineering
0913 Mechanical Engineering
Publication Status: Accepted
Appears in Collections:Faculty of Engineering

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