Outer-layer Self-Similarity of the Turbulent Boundary Layer Based on the Turbulent/non-Turbulent Interface

In this paper, we report on the outer -layer self -similarity of the turbulent boundary layer (TBL) from the perspectives of the turbulent/non-turbulent (T/NT) interface. We receive support from the experimental database of the TBL. The database is measured with particle image velocimetry (PIV) at low to moderate Reynolds number range (Rey = 389-1000). The T/NT interface is detected by the local turbulent kinetic energy method. The intermittency in the outer layer is considered in the velocity decomposition. From our interface perspective, the exponential self -similarity from the mean streamwise velocity is discovered in the outer region. This indicates the consistency of turbulence characteristics in the turbulent region. The outer -layer self -similarity exists above the logarithmic region and below the region linked to the T/NT interface. Based on the two -point correlation, the consistency of the structural spatial characteristics is revealed. Interface -based turbulent fluctuations suggest that the wall -normal scale of the outer -layer structure not only relates to the height from the wall but also needs to consider the distance to the interface. The energy superposition effect of the outer -layer structure is modeled by the structural spatial characteristics. According to the energy superposition effect, for different interface conditions, the structural -based reconsidered turbulent kinetic energy in the outer region is consistent under the interface -based self -similar frame. The proposed interface -based perspective emphasizes that study in the outer intermittent region should not unilaterally consider the wall reference frame. At the same time, the turbulence characteristics in the intermittent region is self -similar from this interface -based reference framework.