Large-scale structures in high reynolds numberwall-bounded turbulence

Abstract

Through comparison of two turbulent boundary layers at vastly different Reynolds numbers, we note that the key features of the very large-scale structures appear to be universal (when scaled with the boundary layer thickness δ). The modulating influence of these large-scale features is analysed through means of conditional averages. It is proposed that the much discussed ‘amplitude modulation’, whereby the large scales modulate the intensity of the small-scale velocity fluctuations, is primarily a near-wall phenomenon, and that further from the surface this may be better described as a ‘preferential arrangement’. In this interpretation, it becomes evident that there is a strong link between the very large-scales that populate the log region and the large-scale interfacial bulging that occurs at the edge of the boundary layers. Conditional averages are presented confirming this finding.