Boundary Layer Studies on Polymer Drag Reduction Using PIV and PLIF

The structure of turbulence in a drag reduced flat plate boundary layer has been studied with particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). Drag reduction was achieved by injection of a solution of water-soluble polymer through a spanwise slot near the leading edge of the flat plate. Velocity and concentration data were obtained using PIV and PLIF, respectively, in planes parallel to the wall (x-z plane) and perpendicular to the wall (x-y plane). Measurements of velocity, vorticity and streak spacing were obtained and trends analyzed. For increasing drag reduction, damping of streak oscillations, suppression of streak splitting and merging, streak stabilization and coarsening of the low speed streaks was observed. PLIF measurements of the injected polymer solution showed that regions of high polymer concentration are correlated with the low speed streaks. PIV measurements in the x-y plane showed that there are significant differences in the statistics of turbulence between boundary layers with polymer injection and channel flow with an ocean of polymer.