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{Ibrahim:2019:10.1017/jfm.2018.905,
author = {Ibrahim, J and Yang, Q and Doohan, P and Hwang, Y},
doi = {10.1017/jfm.2018.905},
journal = {Journal of Fluid Mechanics},
pages = {29--54},
title = {Phase-space dynamics of opposition control in wall-bounded turbulent flows},
url = {http://dx.doi.org/10.1017/jfm.2018.905},
volume = {861},
year = {2019}
}
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RIS format (EndNote, RefMan)

TY  - JOUR
AB  - We investigate the nonlinear phase-space dynamics of plane Couette flow and plane Poiseuille flow under the action of opposition control at low Reynolds numbers in domains close to the minimal unit. In Couette flow, the effect of the control is analysed by focussing on a pair of non-trivial equilibrium solutions. It is found that the control only slightly modifies the statistics, turbulent skin friction and phase-space projection of the lower-branch equilibrium solution, which, in this case, is in fact identical to the edge state. On the other hand, the upper-branch equilibrium solution and mean turbulent state are modified considerably when the control is applied. In phase space, they gradually approach the lower-branch equilibrium solution on increasing the control amplitude, and this results in an elevation of the critical Reynolds number at which the equilibrium solutions first occur via a saddle-node bifurcation. It is also found that the upper-branch equilibrium solution is stabilised by the control. In Poiseuille flow, we study an unstable periodic orbit on the edge state and find that it, too, is modified very little by opposition control. We again observe that the turbulent state gradually approaches the edge state in phase space as the control amplitude is increased. In both flows, we find that the control significantly reduces the fluctuating strength of the turbulent state in phase space. However, the reduced distance between the turbulent trajectory and the edge state yields a significant reduction in turbulence lifetimes for both Couette and Poiseuille flow. This demonstrates that opposition control greatly increases the probability of the trajectory escaping from the turbulent state, which takes the form of a chaotic saddle.
AU  - Ibrahim,J
AU  - Yang,Q
AU  - Doohan,P
AU  - Hwang,Y
DO  - 10.1017/jfm.2018.905
EP  - 54
PY  - 2019///
SN  - 0022-1120
SP  - 29
TI  - Phase-space dynamics of opposition control in wall-bounded turbulent flows
T2  - Journal of Fluid Mechanics
UR  - http://dx.doi.org/10.1017/jfm.2018.905
UR  - http://hdl.handle.net/10044/1/66288
VL  - 861
ER  -
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