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Influence of uniform momentum zones on frictional drag within the turbulent boundary layer |
Kangjun Wang(王康俊)1 and Nan Jiang(姜楠)1,2,† |
1 Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin 300350, China; 2 Tianjin Key Laboratory of Modern Engineering Mechanics, Tianjin 300072, China |
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Abstract Based on a set of experimental databases of turbulent boundary layers obtained from particle image velocimetry in the streamwise-wall-normal plane at friction-velocity-based Reynolds number Reτ =612, the influence of uniform momentum zones (UMZs) on the skin-friction drag is investigated. The skin-friction drag is measured by the single-pixel ensemble correlation method. The results show that the velocity fields with the number of UMZs larger than the mean value have a relatively low skin-friction drag, while the velocity fields with the number of UMZs less than the mean value have a relatively high skin-friction drag. By analyzing the statistical characteristics of UMZs, the dynamic correlation between the UMZs and skin-friction drag is explored. The velocity fields with a low number of UMZs present a sweep event. These sweep motions intensify the small-scale Reynolds shear stress in the near-wall region by modulation effects. The enhancement of small-scale Reynolds shear stress is the direct reason for the high skin-friction drag. Increasing the proportion of velocity fields with high UMZs amount may be a direction to reduce the skin-friction drag within the TBL.
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Received: 17 August 2020
Revised: 05 October 2020
Accepted manuscript online: 05 November 2020
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PACS:
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47.85.lb
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(Drag reduction)
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47.85.ld
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(Boundary layer control)
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47.27.nb
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(Boundary layer turbulence ?)
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47.27.De
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(Coherent structures)
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Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 11732010, 11972251, 11872272, 11902218, and 11802195) and the National Key R&D Program of China (Grant No. 2018YFC0705300). |
Corresponding Authors:
†Corresponding author. E-mail: nanj@tju.edu.cn
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Cite this article:
Kangjun Wang(王康俊) and Nan Jiang(姜楠) Influence of uniform momentum zones on frictional drag within the turbulent boundary layer 2021 Chin. Phys. B 30 034703
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