On the detection of internal interfacial layers in turbulent flows

A novel approach to identify internal interfacial layers, or IILs, in wall-bounded turbulent flows is proposed. Using a Fuzzy Cluster Method (FCM) on the streamwise velocity component, a unique and unambiguous grouping of the Uniform Momentum Zones is achieved, thus allowing the identification of the IILs. The approach overcomes some of the key limitations of the histogram-based IIL identification methods. The method is insensitive to the streamwise domain length, can be used on inhomogeneous grids, uses all the available flow field data, is trivially extended to three dimensions, and does not need user-defined parameters (e.g. number of bins) other than the number of zones, which can be physically justified. The approach is applied to the turbulent boundary layer (experimental, planar PIV) and channel flow (numerical, DNS). The three-dimensional interface identification reveals a streak-like structural organization. The interface is characterized by a strong concentration of spanwise vorticity and is located at the outer edge of the log-layer.