Applicability of Taylor’s Hypothesis for Estimating the Mean Streamwise Length Scale of Large-Scale Structures in the Near-Neutral Atmospheric Surface Layer
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A field investigation of the mean streamwise length scale Lx of large-scale structures and the convection velocity is performed in a high-Reynolds-number (Reτ ~ 106) atmospheric surface layer (ASL). Based on selected high-quality synchronous data obtained at different streamwise positions, the length scale Lx and global convection velocity Uc are extracted in the logarithmic region of the near-neutral ASL at heights of 0.9 m, 1.71 m, 3.5 m, and 5 m. It is found that Uc values are approximately 16% greater than the local mean streamwise velocity component U, and the value of Lx obtained from spatially-separated measurements is greater than the results estimated from Taylor’s hypothesis using the value of U at the four heights. The mean relative difference between the value of Lx and the results estimated by Taylor’s hypothesis using the value of U is approximately 15%. However, the relative difference between the value of Lx and the results estimated from Taylor’s hypothesis using the convection velocity Uc instead of the mean streamwise velocity component U is reduced to 1 ± 6% (≈ zero). Thus, the convection velocity Uc is more appropriate than the mean streamwise velocity component U in obtaining Lx values in the near-neutral ASL.
KeywordsAtmospheric surface layer Convection velocity Large-scale structures Streamwise length scale Taylor’s hypothesis
This work was supported financially by grants from the National Natural Science Foundation of China (11490553, 11702122, and 11421062), and the Fundamental Research Funds for the Central Universities (lzujbky–2017–30). The authors would like to express their sincere appreciation for the support as well as the helpful comments from referees that led to a significant improvement in our work.
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