Some characteristics of low-speed streaks under sheared air-water interfaces |
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Authors: | Wang Shuangfeng Jia Fu |
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Institution: | (1) Institute of Mechanics, Chinese Academy of Sciences, 100080 Beijing, China |
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Abstract: | The characteristics of low-speed fluid streaks occurring under sheared air-water interfaces were examined by means of hydrogen
bubble visualization technique. A critical shear condition under which the streaky structure first appears was determined
to beu
τ≈0.19 cm/s. The mean spanwise streak spacing increases with distance from the water surface owing to merging and bursting
processes, and a linear relationship describing variation of non-dimensional spacing
versusy
+ was found essentially independent of shear stress on the interface. Values of
, however, are remarkably smaller than their counterparts in the near-wall region of turbulent boundary layers. Though low-speed
streaks occur randomly in time and space, the streak spacing exhibits a lognormal probability distribution behavior. A tentative
explanation concerning the formation of streaky structure is suggested, and the fact that
takes rather smaller values than that in wall turbulence is briefly discussed.
The project supported by the National Natural Science Foundation of China (19672070) |
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Keywords: | air-water interface low-speed streak turbulent coherent structure flow visualization |
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