Predicting growth rates of interfaces and internal layers in a turbulent boundary layer using a first order jump model

Experimental research is presented on the characteristics of interfaces and internal layers that are present in a turbulent boundary layer (TBL). Both the turbulent non-turbulent interface (T/NT) and internal shear layers are detected in snapshots of the stereo-PIV data. It turns out that the internal layers exhibit similar characteristics compared to the T/NT interface. A theoretical approximation of the large scale boundary layer growth indicates that the correct boundary layer growth can be obtained by employing a modified first order jump model on the conditional statistics. Employing the same framework to the internal shear layers indicates that shear layers tend to move slower in close proximity to the wall, whereas they accelerate when moving away from the wall. Based on previous research it is believed that these internal layers separate large regions of approximately uniform momentum. Hence, boundary entrainment velocities may be interpreted as growth rates of large scale motions in a TBL.