  We study experimentally and theoretically mixing at the external boundary of
a submerged turbulent jet. In the experimental study we use Particle Image
Velocimetry and an Image Processing Technique based on the analysis of the
intensity of the Mie scattering to determine the spatial distribution of tracer
particles. An air jet is seeded with the incense smoke particles which are
characterized by large Schmidt number and small Stokes number. We determine the
spatial distributions of the jet fluid characterized by a high concentration of
the particles and of the ambient fluid characterized by a low concentration of
the tracer particles. In the data analysis we use two approaches, whereby one
approach is based on the measured phase function for the study of the mixed
state of two fluids. The other approach is based on the analysis of the
two-point second-order correlation function of the particle number density
fluctuations generated by tangling of the gradient of the mean particle number
density by the turbulent velocity field. This gradient is formed at the
external boundary of a submerged turbulent jet. We demonstrate that PDF of the
phase function of a jet fluid penetrating into an external flow and the
two-point second-order correlation function of the particle number density do
not have universal scaling and cannot be described by a power-law function. The
theoretical predictions made in this study are in a qualitative agreement with
the obtained experimental results.
