Wall-attached clusters for the logarithmic velocity law in turbulent pipe flow

What is it about?

We used a novel approach by exploiting clusters of the streamwise velocity fluctuations in the moderate-Reynolds-number TBL. We showed that a group of clusters over a wide range of scales is attached to the wall. These clusters are composed of multiple uniform momentum zones with respect to the wall distance. In addition, we also delineated the structures’ self-similarity and hierarchical features. We found, for the first time to our knowledge, the presence of the logarithmic region by reconstructing the streamwise turbulent intensity from the superposition of the wall-attached clusters without making an a priori assumption or applying a filter.

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Why is it important?

Our results not only show the building blocks for high-Reynolds-number wall turbulence but also present a distinct logarithmic dependence not ‘near’ logarithmic variation that empirically determined in several previous works.