Properties of the streamwise velocity fluctuations in the inertial layer of turbulent boundary layers and their connection to self-similar mean dynamics

Well-resolved streamwise velocity measurements are used to investigate three measures of self-similarity in the spatial inertial sublayer of turbulent boundary layers. The emergence of self-similarity in the inertial sublayer requires a high Reynolds number, and thus a relatively wide range of δ+=δuτ/ν(1400≲δ+≲20,000) is explored. The measures investigated include the Kullback-Leibler divergence (KLD) used in turbulent flow analysis by Tsuji et al. (2005), the logarithmic decrease of the even statistical moments studied by Meneveau and Marusic (2013), and the diagnostic plot of Alfredsson and Örlü (2010). These measures are compared with the analyses of Fife et al. (2005) that determine and exploit an invariant form of the mean momentum equation. A primary focus is on domain(s) where the self-similar behaviors are analytically predicted and empirically observed. The present findings indicate that the approximately constant KLD and approximately logarithmic moment profiles reside in a region that is interior to the bounds of the self-similar inertial domain associated with the mean momentum equation. Conversely, the bounds of the self-similar region on the diagnostic plot correspond closely to the theoretically estimated bounds. Results are briefly discussed relative to Townsend's notion of outer layer similarity, and, on the inertial domain, the physical existence of uniform momentum zones segregated by narrow vortical fissures.