Drag reduction effect by dilute polymer solutions was discovered in 1946 by Toms, but its mechanism is not explained thoroughly despite the enormous progress in understanding the near wall turbulent boundary layer flow in pipes or channels. One of the main problems is relatively poor understanding of dilute polymer solutions and inter-scale transfer of energy in turbulent flows. The polymer effect intensifies in the case of turbulent entrainment across turbulent/non-turbulent interfaces on the boundaries of turbulent jets, wakes or mixing layers. The polymer is sought to alter this region of flow significantly due to the large gradients at the interface and strong interaction of multiple scales - large scales that deflect the interface and the small scales that diffuse the vorticity and strain. An experimental study has been performed to characterize these effects in water - poly(ethylene oxide) solutions, alongside the benchmark case of the fresh water. A new setup was developed to create a spherical localized turbulent patch, thus isolating the polymer effect far from the boundaries with negligible wall friction effects, as opposed to the previously utilized 2D space-filling planar oscillating grids. The setup enables a direct comparison of the results with the direct numerical simulations. We have also developed a system of a repetitive, automatic and consistent solution mixing and performed a large set of particle image velocimetry (PIV) measurements. The algorithm for patch interface detection is proposed and successfully applied to the measurements, revealing the different physical measures of the patch evolution.
