POD analysis of the instability mode of a low-speed streak in a laminar boundary layer

作     者：Si-Chao Deng Chong Pan Jin-Jun Wang Akira Rinoshika 

作者机构：Fluid Mechanics Key Laboratory of Ministry of EducationBeijing University of Aeronautics and Astronautics Department of Mechanical Systems Engineering Yamagata University 

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

年 卷 期：2017年第33卷第6期

页      面：981-991页

核心收录：

学科分类：08[工学] 080103[工学-流体力学] 0802[工学-机械工程] 0701[理学-数学] 0801[工学-力学（可授工学、理学学位）] 0702[理学-物理学] 

基　　金：supported by the National Natural Science Foundation of China (Grants 11372001,11672020,and 11490552) the Fundamental Research Funds for the Central Universities of China (Grant YWF-16-JCTD-A-05) 

主　　题：Low-speed streak Boundary layer transition Streak instability 

摘      要：The instability of one single low-speed streak in a zero-pressure-gradient laminar boundary layer is investigated experimentally via both hydrogen bubble visualization and planar particle image velocimetry(PIV) measurement. A single low-speed streak is generated and destabilized by the wake of an interference wire positioned normal to the wall and in the upstream. The downstream development of the streak includes secondary instability and self-reproduction process, which leads to the generation of two additional streaks appearing on either side of the primary one. A proper orthogonal decomposition(POD) analysis of PIV measured velocity field is used to identify the components of the streak instability in the POD mode space: for a sinuous/varicose type of POD mode, its basis functions present anti-symmetric/symmetric distributions about the streak centerline in the streamwise component, and the symmetry condition reverses in the spanwise component. It is further shown that sinuous mode dominates the turbulent kinematic energy(TKE) through the whole streak evolution process, the TKE content first increases along the streamwise direction to a saturation value and then decays slowly. In contrast, varicose mode exhibits a sustained growth of the TKE content,suggesting an increasing competition of varicose instability against sinuous instability.