A simulation on bypass transition and its key mechanism  

作　　者：DONG Ming ZHOU Heng 

机构地区：[1]Department of Mechanics, Tianjin University [2]Tianjin Key Laboratory of Modern Engineering Mechanics

出　　处：《Science China(Physics,Mechanics & Astronomy)》2013年第4期775-784,共10页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant No. 11102131);the National Basic Research Program of China (Grant No. 2009CB724103);the National Aeronautics Basic Science Foundation of China (Grant No. 2010ZA48002);the Doctoral fund of Ministry of Education of China (Grant No. 20110032120003)

摘　　要：The scenario of bypass transition is generally described theoretically as follows: low-frequency disturbances in the free-stream would generate long stream-wise streaks in the boundary layer, which later would induce secondary instability, leading to rapid increase of high-frequency disturbances, then possibly turbulent spots would emerge, and through their merging, fully developed turbulence appears. This description, however, is insufficient in the sense that it does not provide the explanation on why during the breakdown stage, a large number of waves with different frequencies and wave numbers would appear almost simultaneously, leading to a swift change of the mean flow profile. In this paper, the mechanism leading to this phenomenon is found to be the change of the stability characteristics of mean flow profile, which has a positive feedback effect on the change of the profile itself. And another interesting finding is that, during the transition, the unstable disturbance waves which appear first belong to a branch of inviscid modes, while following the change of the stability characteristics of the mean flow profile, the disturbance waves will change to another branch of inviscid modes, and the latter play the key role in bypass transition.The scenario of bypass transition is generally described theoretically as follows： low-frequency disturbances in the free-stream would generate long stream-wise streaks in the boundary layer, which later would induce secondary instability, leading to rapid increase of high-frequency disturbances, then possibly turbulent spots would emerge, and through their merging, fully developed turbulence appears. This description, however, is insufficient in the sense that it does not provide the explanation on why during the breakdown stage, a large number of waves with different frequencies and wave numbers would appear almost simultaneously, leading to a swift change of the mean flow profile. In this paper, the mechanism leading to this phenomenon is found to be the change of the stability characteristics of mean flow profile, which has a positive feedback effect on the change of the profile itself. And another interesting finding is that, during the transition, the unstable disturbance waves which appear first belong to a branch of inviscid modes, while following the change of the stability characteristics of the mean flow profile, the disturbance waves will change to another branch of inviscid modes, and the latter play the key role in bypass transition.

关 键 词：bypass transition BREAKDOWN INSTABILITY STREAK INVISCID 

分 类 号：O35[理学—流体力学]