Experimental investigation on coherent structures at early stage of boundary layer bypass transition induced by wake impingement  

作　　者：WU Jun PAN Chong LI Tian 

机构地区：[1]Institute of Fluid Mechanics,Beijing University of Aeronautics&Astronautics,Key Laboratory of Fluid Mmechanics Ministry of Education,Beijing 100191,China [2]A V1C l Shenyang A ircraft Design and Research Institute,Shenyang 110035,China

出　　处：《Science China(Technological Sciences)》2012年第11期2981-2989,共9页中国科学（技术科学英文版）

基　　金：supported by the National Natural Science Foundation of China (Grant No. 10832001)

摘　　要：The early stage of a boundary layer bypass transition induced by the direct impingement of a circular cylinder wake is experimentally investigated in water tunnel,with the primary interest in both the evolution of coherent structures and their effects on the disturbance growth inside the boundary layer.It is found that spanwise vortices with small scale first form in the near-wall region around the leading-edge,which are either the residual of the wake rollers cut by the leading-edge or the high-order structures induced by the wake rollers.The formation of these spanwise vortices leads to the first rapid disturbance growth inside the boundary layer.On the other hand,streamwise vortices,which result from the impingement of longitudinal braids onto the leading-edge,are also observed inside the boundary layer.They lead to the three dimensional destabilization and the subsequent dispersion of spanwise vortices,and soon become the most dominant coherent structures inside the transitional boundary layer.It is suggested that the formation and evolution of these streamwise vortices contribute to the secondary disturbance growth stage and thus promote the completion of the transition process.The difference between the present transition scenario triggered by direct wake impingement and that by indirect wake-vortex inducement is further discussed.

关 键 词：circular cylinder wake flat-plate boundary layer bypass transition coherent structures 

分 类 号：O357.5[理学—流体力学] O357.4[理学—力学]