Turbulent/non-turbulent interface detection for wall-bounded flows

The intermittency between laminar and turbulent flow is a well known feature in the outer region of turbulent boundary layers.  Detecting the complex interface between irrotational fluid and inhomogeneous turbulence and understanding the physical processes occurring at the interface have achieved a lot of scientific attention. However, no universal method to detect the turbulent/non-turbulent interface (TNTI) has been established. This holds in particular for high Reynolds number experimental data where the spatial resolution is limited due to the requirement of resolving the entire intermittent region. Therefore, this work analyzes the sensitivity of TNTI detection approaches. The techniques considered are based on the turbulent kinetic energy, the homogeneity of the potential flow region and the particle image density.  The effect of bias errors is studied on both instantaneous snapshots and also with respect to statistically averaged quantities such as the intermittency factor and the length of the TNTI. In addition, the suitable working range for the techniques is outlined and several possible applications that can contribute to a better understanding of turbulent boundary layers are indicated.