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Acta Mechanica Sinica

, Volume 29, Issue 4, pp 485–493 | Cite as

A study on coherent structures and drag-reduction in the wall turbulence with polymer additives by TRPIV

  • Xin-Lei Guan
  • Shi-Yong Yao
  • Nan JiangEmail author
Research Paper

Abstract

An experimental measurement was performed using time-resolved particle image velocimetry (TRPIV) to investigate the spatial topological character of coherent structures in wall-bounded turbulence of polymer additive solution. The fully developed near-wall turbulent flow fields with and without polymer additives at the same Reynolds number were measured by TRPIV in a water channel. The comparisons of turbulent statistics confirm that due to viscoelastic structure of long-chain polymers, the wall-normal velocity fluctuation and Reynolds shear stress in the near-wall region are suppressed significantly. Furthermore, it is noted that such a behavior of polymers is closely related to the decease of the motion of the second and forth quadrants, i.e., the ejection and sweep events, in the near-wall region. The spatial topological mode of coherent structures during bursts has been extracted by the new mu-level criteria based on locally averaged velocity structure function. Although the general shapes of coherent structures are unchanged by polymer additives, the fluctuating velocity, velocity gradient, velocity strain rate and vorticity of coherent structures during burst events are suppressed in the polymer additive solution compared with that in water. The results show that due to the polymer additives the occurrence and intensity of coherent structures are suppressed, leading to drag reduction.

Keywords

Time-resolved particle image velocimetry Wall-bounded turbulence Coherent structures Polymer additives Drag reduction 

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Copyright information

© The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Department of MechanicsTianjin UniversityTianjinChina
  2. 2.Tianjin Key Laboratory of Modern Engineering MechanicsTianjinChina
  3. 3.The State Key Laboratory of Nonlinear Mechanics, Institute of MechanicsChinese Academy of SciencesBeijingChina
  4. 4.Nankai University-Tianjin University Center for Liu Hui Applied MathematicsTianjinChina

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