Effects of mean shear on the local turbulent entrainment process

We report on effects of mean shear on the turbulent entrainment process focusing in particular on their relation to small scale processes in the proximity of the turbulent/non-turbulent interface (TNTI). Three-dimensional particle tracking velocimetry measurements of an axisymmetric jet are compared to data from a direct numerical simulation of a zero-mean-shear flow. Conditional statistics relative to the interface position are investigated in a pseudo-Eulerian (i.e. in a fixed frame relative to the interface position) and in a Lagrangian view. A mapping between distance to the instantaneous interface versus conditional time along the trajectory shows that entraining particles remain initially close to the TNTI. Furthermore, decomposing the local entrainment velocity $v_n$ into mean and fluctuating components, we find that mean shear enhances the local entrainment velocity via inviscid and viscous effects.