Uniform momentum zones and internal shear layers in turbulent pipe flow

This study explores uniform momentum zones (UMZs) and their interfaces using direct numerical simulation data of fully-developed turbulent pipe flow at Reynolds number ranging from Re_τ = 550–6000. We identify UMZs and their corresponding interfaces by applying a histogram-based identification method, as proposed by Adrian et al. (J. Fluid Mech., vol. 422, 2000, pp. 209–331) and de Silva et al. (J. Fluid Mech., vol 786, 2016, pp. 209–331). We find that the number of UMZs exhibits a log-linear increase with the Reynolds number in a manner analogous to that reported in turbulent boundary layers. The topmost UMZs are demarcated by a streamwise velocity at 0.95U_CL (where U_CL is the centerline mean velocity) across a wide range of the Reynolds number, indicating the presence of a quiescent core region. We further investigate the turbulent statistics across the interfaces (or internal shear layers) of multiple UMZs. We will discuss the scaling of these interfaces and their relationship with the logarithmic mean velocity profile.