Transition region where the large-scale and very large scale motions coexist in atmospheric surface layer: wind tunnel investigation

The turbulent structures in atmospheric surface layer (ASL) are investigated in wind tunnel with hot-wire anemometers in present study. The results show that there exist two typical turbulent structures characterised by their streamwise length scales, i.e. large-scale motions (LSMs) and very large scale motions (VLSMs) as reported recently in pipe flow, channel flow, zero-pressure-gradient turbulent boundary layers and near-neutral ASLs. Moreover, a transition region containing both LSMs and VLSMs is first reported in present investigation, and this region depends on the Reynolds numbers. In the transition region, as the wall-normal distance increases, the turbulent energy ratio of LSMs is gradually weakened but VSLMs strengthened.