Imperial College London
Alternate

Dr. Yongyun Hwang

Faculty of Engineering, Department of Aeronautics

Reader in Fluid Mechanics
 
 
 
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Contact

 

+44 (0)20 7594 5078y.hwang

 
 
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Location

 

337City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{de:2017:10.1017/jfm.2017.697,
author = {de, Giovanetti M and Sung, HJ and Hwang, Y},
doi = {10.1017/jfm.2017.697},
journal = {Journal of Fluid Mechanics},
pages = {483--513},
title = {Streak instability in turbulent channel flow: the seeding mechanism of large-scale motions},
url = {http://dx.doi.org/10.1017/jfm.2017.697},
volume = {832},
year = {2017}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - It has often been proposed that the formation of large-scale motion (or bulges) is aconsequence of successive mergers and/or growth of near-wall hairpin vortices. In thepresent study, we report our direct observation that large-scale motion is generated byan instability of an ‘amplified’ streaky motion in the outer region (i.e. very-large-scalemotion). We design a numerical experiment in turbulent channel flow up to Reτ '2000where a streamwise-uniform streaky motion is artificially driven by body forcing inthe outer region computed from the previous linear theory (Hwang & Cossu, J. FluidMech., vol. 664, 2015, pp. 51–73). As the forcing amplitude is increased, it is foundthat an energetic streamwise vortical structure emerges at a streamwise wavelength ofλx/h '1–5 (h is the half-height of the channel). The application of dynamic modedecomposition and the examination of turbulence statistics reveal that this structureis a consequence of the sinuous-mode instability of the streak, a subprocess of theself-sustaining mechanism of the large-scale outer structures. It is also found that thestatistical features of the vortical structure are remarkably similar to those of the largescalemotion in the outer region. Finally, it is proposed that the largest streamwiselength of the streak instability determines the streamwise length scale of very-largescalemotion.
AU  - de,Giovanetti M
AU  - Sung,HJ
AU  - Hwang,Y
DO  - 10.1017/jfm.2017.697
EP  - 513
PY  - 2017///
SN  - 0022-1120
SP  - 483
TI  - Streak instability in turbulent channel flow: the seeding mechanism of large-scale motions
T2  - Journal of Fluid Mechanics
UR  - http://dx.doi.org/10.1017/jfm.2017.697
UR  - http://hdl.handle.net/10044/1/51434
VL  - 832
ER  -
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