Communication between the buffer layer and the wall in a turbulent channel flow

•Spanwise correlations of filtered velocity field provide signatures of active eddies.•Spanwise correlations of streamwise velocity lead to the consensual streak spacing.•Periodicity in the spanwise velocity correlations comes from the vortex clusters.•Ejection/sweep pairs increase the wall shear stress intensity by stretching.•Large scales affect all the correlations, except those of the wall normal velocity. Direct numerical simulations obtained in large computational domains of a fully developed turbulent channel flow up to the Karman number 1100 are analyzed to determine the scaling of the spanwise correlation coefficients and the effect of the outer eddies. The local fluctuating velocity field is narrow-band-pass and low-pass filtered along the streamwise wavenumber. The spanwise correlations of the narrow-band passed signals in the low buffer layer adequately provide length scales and signatures of the active structures. The low-pass filtering is used to investigate the relative role of the outer eddies. The impact of the active and passive eddies on the wall is analyzed separately through the cross-correlations of the filtered velocity field with the wall shear stress fluctuations. Characteristic length-scales resulting from the analysis of the velocity field differ depending on the quantity and some are related to the conventional streak spacing but not all. The quasi-streamwise vortex paradigm, for the most part, allows the interpretation of these characteristics, but fails in some cases.