Abstract
The hairpin vortex structures in the boundary layer with \({Re}_{\theta }\) = 159–239 of a square tube were studied experimentally using the moving single- frame and long-exposure image (M-SFLE) method. And the Liutex vortex identification criteria are used to confirm vortices and characterize their strength in the experimental results. The flow measurement system always moves at the same or similar speed as vortices in the boundary layer to track vortex structures continuously. The experimental results show that the secondary hairpin vortex and the tertiary hairpin vortex can be induced by the primary hairpin vortex. And the extension of the vortex packet in the flow direction can lead to the occurrence of vortex merging in the near-wall turbulent boundary layer. The Q2 event plays a key role in the formation of secondary hairpin vortices and the merging behaviors. The merging process of two vortices can be divided into three stages and the strength of the vortex structures has unique characteristics in different stages.
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Li, Y., Dong, X., Cai, X., Zhou, W., Tang, X. (2023). Experimental Studies on the Evolution of Hairpin Vortex Package in the Boundary Layer of a Square Tube. In: Wang, Y., Gao, Y., Liu, C. (eds) Liutex and Third Generation of Vortex Identification. Springer Proceedings in Physics, vol 288. Springer, Singapore. https://doi.org/10.1007/978-981-19-8955-1_9
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