Rheo-optical investigations and near-wall turbulence structure of polymer solutions in turbulent channel flow

In the present study, the turbulence behavior of polymer solutions is investigated using laser-Doppler velocimetry (LDV). At the same time, an attempt is made to determine a possibly occurring extension and orientation of the macromolecules by flow-induced birefringence (FIB). Flow-dynamic and rheo-optical experiments are presented which were performed in a smooth square channel in the area of the fully developed turbulent flow. The turbulent flow properties of aqueous solutions of PAAM and Xanthan Gum were studied. The Reynolds' number was 30.000. The concentration of the polymer solutions was varied between 300 and 800 wppm for Praestol 2300 and between 30 and 120 wppm in the case of Xanthan Gum. The experimental data obtained indicate a significant dependence of the turbulent flow properties on the molecular structure of the polymers used. This could be clearly demonstrated by the values of the root mean square (rms) of the velocity fluctuation. Furthermore, the influence of the extension and orientation of the macromolecules on the turbulent flow properties was investigated.