Statistical imprints of structure in wall turbulence

Statistical imprints of both small- and large-scale structures in the outer layer of wall turbulence are studied using large ensembles of experimental data. Instantaneous velocity and acceleration fields have been measured over a broad Reynolds-number range (550 < Re _τ < 2433) in the streamwise-wall-normal plane of fully-developed turbulent channel flow using particle-image velocimetry and particle-image accelerometry. Multi-point statistics of velocity and acceleration are computed from this data and average length scales are determined from the statistics. These average length scales are found to be consistent with the spatial extents of the vortical structures often observed in instantaneous velocity realizations of wall turbulence. In addition, these length scales exhibit clear trends with both wall-normal position and Reynolds number.