Coherent structures over riblets in turbulent boundary layer studied by combining time-resolved particle image velocimetry(TRPIV),proper orthogonal decomposition(POD),and finite-time Lyapunov exponent(FTLE)

作     者：Shan Li Nan Jiang Shaoqiong Yang Yongxiang Huang Yanhua Wu 李山;姜楠;杨绍琼;黄永祥;吴彦华

作者机构：School of Mechanical Engineering Tianjin University Tianjin 300072 China Xiamen University Xiamen 361102 China Nanyang Technological University Singapore 639798 Republic of Singapore 

出 版 物：《Chinese Physics B》 (中国物理B（英文版）)

年 卷 期：2018年第27卷第10期

页      面：395-404页

核心收录：

学科分类：08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 

基　　金：Project supported by the National Natural Science Foundation of China(Grant Nos.11332006,11732010,11572221,and 11502066) the Natural Science Foundation of Tianjin City(Grant No.18JCQNJC5100) 

主　　题：turbulent boundary layer riblets proper orthogonal decomposition finite-time Lyapunov exponent 

摘      要：Time-resolved particle image velocimetry（TRPIV） experiments are performed to investigate the coherent structure＇s performance of riblets in a turbulent boundary layer（TBL） at a friction Reynolds number of 185. To visualize the energetic large-scale coherent structures（CSs） over a smooth surface and riblets, the proper orthogonal decomposition（POD） and finite-time Lyapunov exponent（FTLE） are used to identify the CSs in the TBL. Spatial-temporal correlation is implemented to obtain the characters and transport properties of typical CSs in the FTLE fields. The results demonstrate that the generic flow structures, such as hairpin-like vortices, are also observed in the boundary layer flow over the riblets, consistent with its smooth counterpart. Low-order POD modes are more sensitive to the riblets in comparison with the high-order ones,and the wall-normal movement of the most energy-containing structures are suppressed over riblets. The spatial correlation analysis of the FTLE fields indicates that the evolution process of the hairpin vortex over riblets are inhibited. An apparent decrease of the convection velocity over riblets is noted, which is believed to reduce the ejection/sweep motions associated with high shear stress from the viscous sublayer. These reductions exhibit inhibition of momentum transfer among the structures near the wall in the TBL flows.