Accurate measurement of wall skin friction by single-pixel ensemble correlation

Shen, JunQi; Pan, Chong; Wang, Jinjun

doi:10.1007/s11433-014-5462-9

Cited by 18 publications

(10 citation statements)

References 27 publications

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“…Obviously, how to determine  u accurately is extremely important. Unfortunately, despite loads of researches [36][37][38][39][40] in recent years, it is still a big challenge for fluid mechanics community. The logarithmic law profile of streamwise mean velocity can be expresses as…”

Section: Turbulence Statisticmentioning

confidence: 99%

Effect of hierarchical structured superhydrophobic surfaces on coherent structures in turbulent channel flow

Tian

Zhang

Jiang

et al. 2015

Experimental Thermal and Fluid Science

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Section: Turbulence Statisticmentioning

confidence: 99%

Effect of hierarchical structured superhydrophobic surfaces on coherent structures in turbulent channel flow

Tian

Zhang

Jiang

et al. 2015

Experimental Thermal and Fluid Science

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“…When the ensemble size is above 1000, the relative error is about 1%, while the ensemble size of image samples exceeds 2000, the relative error will be below 0.1%. [27] 034703-2 The flow parameters of the boundary layer are listed in Table 1. The log-law constants of mean velocity profile κ = 0.41 and B = 5.0.…”

Section: Methodsmentioning

confidence: 99%

“…[24,25] Own to the high spatial resolution, the SPEC can measure the mean velocity profile in the viscous sublayer, and get a reliable value of skin-friction drag by estimating the slope of the mean streamwise velocity profile in the viscous sublayer. [26,27] The more details of SPEC can be referred to Westerweel et al [24] and Kähler et al [25] The objective of the present study is to explore the influence of UMZs on the skin-friction drag and to examine the statistic characteristics of UMZs within the TBL. The experimental dataset analyzed in this work was obtained from time-resolved particle image velocimetry (TRPIV).…”

Section: Introductionmentioning

confidence: 99%

Influence of uniform momentum zones on frictional drag within the turbulent boundary layer*

Wang¹,

Jiang²

2021

Chinese Phys. B

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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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“…[25] Previous studies have concluded that circular synthetic jet can produce drag reduction effect and periodically generate hairpin vortex structure. In this paper, the time-resolved particle image velocimetry (TR-PIV) system is utilized to implement the quantitative measurements of the flow field under the influence of the synthetic jet actuator (SJA), and the wall friction velocity is calculated by the single-pixel ensemble correlation [26,27] (SPEC). The velocity fields of streamwisewall-normal plane and streamwise-spanwise plane are collected, and then the generation process of hairpin vortex and the drag reduction mechanism of synthetic jet in these two planes are studied.…”

Section: Introductionmentioning

confidence: 99%

Effects of single synthetic jet on turbulent boundary layer

Zhang

Wang

et al. 2022

Chinese Phys. B

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The turbulent boundary layer (TBL) was actively controlled by the synthetic jet generated from a circular hole. According to datasets of velocity fields acquired by a time-resolved particle image velocimetry (TR-PIV) system, the average drag reduction rate of 6.2% was obtained downstream of the hole with control. The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream, while the reverse vortex decays rapidly. By statistical average, it can be found that a low-speed streak is generated downstream. Induced by the two vortex legs, the fluid under them converges to the middle. The drag reduction effect produced by the synthetic jet is local, and it reaches the maximum at x + = 400, where the drag reduction rate reaches about 12.2%. After extraction of coherent structure by the spatial two-point correlation analysis, it can be seen that the synthetic jet suppresses the streamwise scale and wall-normal scale of the large-scale coherent structure, and slightly weakens the spanwise motion to achieve the effect of drag reduction.

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Accurate measurement of wall skin friction by single-pixel ensemble correlation

Cited by 18 publications

References 27 publications

Effect of hierarchical structured superhydrophobic surfaces on coherent structures in turbulent channel flow

Effect of hierarchical structured superhydrophobic surfaces on coherent structures in turbulent channel flow

Influence of uniform momentum zones on frictional drag within the turbulent boundary layer*

Effects of single synthetic jet on turbulent boundary layer

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