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ONE MECHANISM OF HAIRPIN VORTEX GENERATION BASED ON STREAK TRANSIENT GROWTH

Y. S. Wang
Department of Engineering Mechanics, School of Aerospace Tsinghua University Beijing 100084, PR China

Chunxiao Xu
Department of Engineering Mechanics Tsinghua University Beijing 100084, PR China

Weixi Huang
Department of Engineering Mechanics Tsinghua University Beijing 100084, PR China

Guixiang Cui
Department of Engineering Mechanics, Tsinghua University, Beijing, China 100084

Résumé

The vortical structures due to the streak transient growth is studied by direct numerical simulations of the minimal channel flow at Reτ = 400. The streak profile is obtained by conditional averaging the DNS data of fully developed turbulent channel flow, in which the linearly stable streaks are prevailing. Therefore, the stable streak with moderate strength is selected and the sinuous perturbation of spanwise velocity is imposed initially. The generation of a complete hairpin vortex structure as well as the hairpin packet is observed. The mechanism for the formation of hairpin vortex is analyzed by using the vorticity transport equation along the vortex lines. The stretching and titling of the vortex lines play a significant role in the generation of the hairpin vortex.