Quantitative Characterization of Streaky Structures in Open-Channel Flows

Streaky structures have been reported in open-channel flows by various investigations in the inner and outer layer. Although the ubiquity of streaks is well recognized, it remains unclear how the streaky structures in the inner and outer layers are related to each other. This paper employs a unified algorithm to identify streaky structures which can be applied in both inner and outer layers with exactly the same subjective threshold. The characteristic scales of streaky structures are quantified, including the width and the spanwise spacing. The results reveal that the spatial scales increase from the near-wall region to the outer layer. The continuous linear growth trend indicates a close relationship between the streaky structures in the inner and outer layers, which can be plausibly explained with the attached-eddy hypothesis.