Influence of wall-attached structures on the interface of the quiescent core region in turbulent pipe flow*

The quiescent core region in pipe flow is explored using the direct numerical simulation data of turbulent pipe flow at Reτ = 926. The quiescent core region is one of the uniform momentum zones and contains the highest convection velocity in turbulent pipe flow. The interface of the quiescent core region has a similar physical behavior to the turbulent/non-turbulent interface and underlying internal layer. The turbulent structures in pipe flow are detected by using the percolation theory. The wall-attached structure is closely associated with geometrical characteristics of the interface and entrainment, which is a transport phenomenon at the interface. The wall-attached structure has a huge influence on dynamics in the vicinity of the interface. The wall-attached u-structure acquired in the present work is a structure that is subject to the attached-eddy hypothesis, and the influence of the wall-attached structures near the interface varies according to height change of the wall-attached structures. Finally, dynamics of the interface is reconstructed using conditional statistics according to the growth of the wall-attached structure.