Imperial College London
Professor Xuesong Wu

ProfessorXuesongWu

Faculty of Natural Sciences, Department of Mathematics

Professor of Applied Mathematics
 
 
 
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Contact

 

+44 (0)20 7594 8494x.wu Website

 
 
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Location

 

738Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Citation

BibTex format

@article{Wu:2016:10.1017/jfm.2015.646,
author = {Wu, X and Zhuang, X},
doi = {10.1017/jfm.2015.646},
journal = {Journal of Fluid Mechanics},
pages = {396--439},
title = {Nonlinear dynamics of large-scale coherent structures in turbulent free shear layers},
url = {http://dx.doi.org/10.1017/jfm.2015.646},
volume = {787},
year = {2016}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - Fully developed turbulent free shear layers exhibit a high degree of order, characterized by large-scale coherent structures in the form of spanwise vortex rollers. Extensive experimental investigations show that such organized motions bear remarkable resemblance to instability waves, and their main characteristics, including the length scales, propagation speeds and transverse structures, are reasonably well predicted by linear stability analysis of the mean flow. In this paper, we present a mathematical theory to describe the nonlinear dynamics of coherent structures. The formulation is based on the triple decomposition of the instantaneous flow into a mean field, coherent fluctuations and small-scale turbulence but with the mean-flow distortion induced by nonlinear interactions of coherent fluctuations being treated as part of the organized motion. The system is closed by employing a gradient type of model for the time- and phase-averaged Reynolds stresses of fine-scale turbulence. In the high-Reynolds-number limit, the nonlinear non-equilibrium critical-layer theory for laminar-flow instabilities is adapted to turbulent shear layers by accounting for (1) the enhanced non-parallelism associated with fast spreading of the mean flow, and (2) the influence of small-scale turbulence on coherent structures. The combination of these factors with nonlinearity leads to an interesting evolution system, consisting of coupled amplitude and vorticity equations, in which non-parallelism contributes the so-called translating critical-layer effect. Numerical solutions of the evolution system capture vortex roll-up, which is the hallmark of a turbulent mixing layer, and the predicted amplitude development mimics the qualitative feature of oscillatory saturation that has been observed in a number of experiments. A fair degree of quantitative agreement is obtained with one set of experimental data.
AU  - Wu,X
AU  - Zhuang,X
DO  - 10.1017/jfm.2015.646
EP  - 439
PY  - 2016///
SN  - 1469-7645
SP  - 396
TI  - Nonlinear dynamics of large-scale coherent structures in turbulent free shear layers
T2  - Journal of Fluid Mechanics
UR  - http://dx.doi.org/10.1017/jfm.2015.646
UR  - http://hdl.handle.net/10044/1/30699
VL  - 787
ER  -
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