【摘要】 以Del-Alamo等(2004)直接数值模拟的槽道紊流数据为基础,对比两种涡旋方向的计算方法(涡量矢量和速度梯度张量的实特征向量),并统计了涡旋与3个切面(XZ,XY及YZ)间倾角的概率密度分布.研究结果表明,在缓冲层内,涡量矢量与实特征向量存在较大的差异;涡旋以准流向涡为主,其与XZ面的倾角很小,但与YZ面的倾角很大.在缓冲层外,涡量矢量与实特征向量的夹角较小,且概率密度最大的夹角稳定在10°附近;涡旋以发夹涡为主,与XZ面主要呈±45°倾角,与XY及YZ面主要呈±55°倾角.涡旋与切面间倾角的概率密度分布特征可以由Ω状发夹涡模型来解释.更多还原

【Abstract】 The study presents analysis of vortex orientation characterized by vorticity vector and real eigenvector of the velocity gradient tensor. The analysis was based on DNS data of channel flow from Del-Alamo et al( 2004). The intersection angle β between real eigenvector and vorticity vector is relatively large in the buffer layer and small in the outer layer,and its most probable value is about 10°. The real eigenvector is more appropriate for characterizing the elevation angle α made by vortex orientation with three sliced orthogonal planes. Quasi-streamwise vortices dominate the buffer region,rendering small α with the XZ plane and large α with the YZ plane. In the wake region,hairpin vortices are common,and they yield peaks of α at ± 45°in the XZ plane and ± 55° in XY and YZ planes. The Ω-shaped hairpin vortex model appears to plausibly interpret the general feature of PDF of elevation angle.更多还原