Organised motions in turbulent boundary layers over a wide range of Reynolds number

The motivation behind this paper comes from the large-scale coherence that has been recently reported in the near-wall and logarithmic regions of wall-bounded turbulent flows. Associated with these are inclined vortical structures that populate the near-wall region. Most often these inclined structures have been inferred as hairpin shaped vortices that have been observed experimentally and evidenced using conditional averaging and two-point correlations. The objective of this study is to analyse three-component velocity fields and determine the instantaneous three-dimensional structure around these large-scale coherent motions and their concurrent existence in the laboratory and the neutral atmospheric surface layer. Starting from two-point correlation we further extend the interrogation of these structures via the instantaneous flow field. The instantaneous spanwise velocity field clearly shows the presence of vortical features that resemble the hairpin vortices. Results for spectra for the spanwise velocity component show that energy of large scales (∼ 6δ) increases with increasing Reynolds number just like the streamwise component.