Investigation of Turbulent-Mixing-Layer Flow with Polymer Additives and Bubble Injection by Particle Image Velocimetry

Turbulent-mixing-layer flows in a vertical channel with polymer additives and bubble injection were experimentally studied by particle image velocimetry (PIV). The transparent test section was 1.0 m long with a 0.04 m x 0.11 m cross section, and the main stream was split into two substreams by a specially designed splitter. The velocities on the low- and high-speed sides are 0.36 m/s and 1.4 m/s, respectively. The Reynolds number based on the velocity difference between the two streams and the vorticity thickness delta at the trailing edge of the splitter was 13,500 for the pure water mixing-layer flow. Aquesous (200 ppm) Polyacrylamide (PAM) solutions and pure water were used as the liquid phase, and gas bubbles with a 0.5% void fraction were injected into the mixing-layer containing polymer additives, from the center of the splitter end, to check the influence of polymer additives and bubbles on the turbulent structure and properties. The distribution of the turbulence properties changed more significantly for the mixing-layer in the polymer additive case than in the pure water case. In the latter case, the Reynolds shear stress (RSS) peak was less than that for the pure water case at the same downstream cross section, but the vorticity peak in the polymer additive case was larger than that in the pure water case in the region the mixing-layer developed (x < 5 delta). However, upon bubble injection, the effect of the polymer additives was diminished.