Imperial College London
Alternate

ProfessorGeorgePapadakis

Faculty of Engineering, Department of Aeronautics

Professor of Aerodynamics
 
 
 
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Contact

 

+44 (0)20 7594 5080g.papadakis

 
 
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Location

 

331City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Paul:2017:10.1017/jfm.2017.54,
author = {Paul, I and Papadakis, G and Vassilicos, JC},
doi = {10.1017/jfm.2017.54},
journal = {Journal of Fluid Mechanics},
pages = {295--332},
title = {Genesis and evolution of velocity gradients in a near-field spatially developing turbulence},
url = {http://dx.doi.org/10.1017/jfm.2017.54},
volume = {815},
year = {2017}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - This paper investigates the dynamics of velocity gradients for a spatially developing flowgenerated by a single square element of a fractal square grid at low inlet Reynolds numberthrough direct numerical simulation. This square grid-element is also the fundamentalblock of a classical grid. The flow along the grid-element centreline is initially irrotationaland  becomes  turbulent  further  downstream  due  to  the  lateral  excursions  of  vorticalturbulent wakes from the grid-element bars. We study the generation and evolution ofthe symmetric and anti-symmetric parts of the velocity gradient tensor for this spatiallydeveloping flow using the transport equations of mean strain-product and mean enstrophyrespectively. The choice of low inlet Reynolds number allows for fine spatial resolutionand long simulations, both of which are conducive in balancing the budget equations ofthe above quantities. The budget analysis is carried out along the grid-element centrelineand the bar centreline. The former is observed to consist of two subregions: one in theimmediate  lee  of  the  grid-element  which  is  dominated  by  irrotational  strain,  and  onefurther  downstream  where  both  strain  and  vorticity  coexist.  In  the  demarcation  areabetween these two subregions, where the turbulence is inhomogeneous and developing,the energy spectrum exhibits the best−5/3 power law slope. This is the same locationwhere  the  experiments  at  much  higher  inlet  Reynolds  number  show  a  well  defined−5/3 spectrum over more than a decade of frequencies. Yet, the Q-R diagram remainsundeveloped in the near grid-element region, and both the intermediate and extensivestrain-rate eigenvectors align with the vorticity vector. Along the grid-element centreline,the  strain  is  the  first  velocity  gradient  quantity  generated  by  the  action  of  pressureHessian.  This  strain  is  then  transported  downstream  by  fluctuations  and  strain  self-amplification is activate
AU  - Paul,I
AU  - Papadakis,G
AU  - Vassilicos,JC
DO  - 10.1017/jfm.2017.54
EP  - 332
PY  - 2017///
SN  - 1469-7645
SP  - 295
TI  - Genesis and evolution of velocity gradients in a near-field spatially developing turbulence
T2  - Journal of Fluid Mechanics
UR  - http://dx.doi.org/10.1017/jfm.2017.54
UR  - http://hdl.handle.net/10044/1/44173
VL  - 815
ER  -
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