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

作     者：Xin-Lei Guan Shi-Yong Yao Nan Jiang 

作者机构：Department of Mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering Mechanics The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Nankai University-Tianjin University Center for Liu Hui Applied Mathematics 

出 版 物：《Acta Mechanica Sinica》 (力学学报（英文版）)

年 卷 期：2013年第29卷第4期

页      面：485-493页

核心收录：

学科分类：080704[工学-流体机械及工程] 080103[工学-流体力学] 08[工学] 0807[工学-动力工程及工程热物理] 081304[工学-建筑技术科学] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 0813[工学-建筑学] 0801[工学-力学（可授工学、理学学位）] 

基　　金：supported by the National Natural Science Foundation of China(11272233) National Key Basic Research and Development Program(2012CB720101) 2012 opening subjects of The State Key Laboratory of Nonlinear Mechanics(LNM),Institute of Mechanics,Chinese Academy of Sciences 

主　　题：Time resolved particle image velocimetry ~ Wall bounded turbulence ~ Coherent structures ~ Polymer addi tives ~ Drag reduction 

摘      要：An experimental measurement was performed us- ing time-resolved particle image velocimetry （TRPIV） to in- vestigate the spatial topological character of coherent struc- tures in wall-bounded turbulence of polymer additive solu- tion. 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 compar- isons 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 spa- tial 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 com- pared 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.