Turbulent Channels, Pipes and Boundary Layers: Similarities and Differences in Large Scale Motions

Abstract

This paper detais a prelminary comparison between the energy spectra of streamwise velocity fluctuations i ero-pressure-gradient flat-plate turbulent boundary layers TBL) and turbulent pipe and channel flows. The unique facities avaiable at the University of Melbourne enable us to investigate these three flows at matched friction Reynolds numbers Re and matched viscous-scaled hot-wire lengths l+. Detaied maps of energy spectra calculated from time-series data) reveal important differences between these two flows, particularly in the very large-scale structures that exist in the log and inner wake regions. It is also noted that differences in the large-scale energy between the three geometries extend all the way to the wall. Hence, the commonly held view that the near-wall region is the same across nternal and external flows is not strictly true. In general we would recommend caution when comparing statistics between external and internal turbulent flows, especialy with ncreasing Reynolds number.