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Using Finite-Time Lyapunov Exponents (FTLE) method, Lagrangian coherent structures (LCSs) in a fully developed flat-plate
turbulent boundary layer are successfully identified from a two-dimensional (2D) velocity field obtained by time-resolved
2D PIV measurement. The typical LCSs in the turbulent boundary layer are hairpin-like structures, which are characterized
as legs of quasi-streamwise vortices extending deep into the near wall region with an inclination angle θ to the wall, and heads of the transverse vortex tube located in the outer region. Statistical analysis on the characteristic
shape of typical LCS reveals that the probability density distribution of θ accords well with t-distribution in the near wall region, but presents a bimodal distribution with two peaks in the outer region, corresponding
to the hairpin head and the hairpin neck, respectively. Spatial correlation analysis of FTLE field is implemented to get the
ensemble-averaged inclination angle θ
R of typical LCS. θ
R first increases and then decreases along the wall-normal direction, similar to that of the mean value of θ. Moreover, the most probable value of θ saturates at y
+=100 with the maximum value of about 24°, suggesting that the most likely position where hairpins transit from the neck to
the head is located around y
+=100. The ensemble- averaged convection velocity U
c of typical LCS is finally calculated from temporal-spatial correlation analysis of FTLE field. It is found that the wall-normal
profile of the convection velocity U
c(y) accords well with the local mean velocity profile U(y) beyond the buffer layer, evidencing that the downstream convection of hairpins determines the transportation properties
of the turbulent boundary layer in the log-region and beyond.
Supported by the National Natural Science Foundation of China (Grant Nos. 10425207 and 10832001) 相似文献
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Anna S. Barashkova Dmitry Y. Ryazantsev Eugene A. Rogozhin 《Molecules (Basel, Switzerland)》2022,27(11)
Plant antimicrobial peptides from the α-hairpinins family (hairpin-like peptides) are known to possess a wide range of biological activities. However, less is known about the structural determinants of their antimicrobial activity. Here, we suggest that spatial structure as well as surface charge and hydrophobicity level contribute to the antimicrobial properties of α-hairpinin EcAMP1 from barnyard grass (Echinochloa cruss-galli) seeds. To examine the role of the peptide spatial structure, two truncated forms of EcAMP1 restricted by inner and outer cysteine pairs were synthesized. It was shown that both truncated forms of EcAMP1 lost their antibacterial activity. In addition, their antifungal activity became weaker. To review the contribution of surface charge and hydrophobicity, another two peptides were designed. One of them carried single amino acid substitution from tryptophan to alanine residue at the 20th position. The second one represented a truncated form of the native EcAMP1 lacking six C-terminal residues. But the α-helix was kept intact. It was shown that the antifungal activity of both modified peptides weakened. Thereby we can conclude that the secondary structural integrity, hydrophobic properties, and surface charge all play roles in the antimicrobial properties of α-hairpinins. In addition, the antibacterial activity of cereal α-hairpinins against Gram-positive bacteria was described for the first time. This study expands on the knowledge of structure–function interactions in antimicrobial α-hairpinins. 相似文献
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