The influence of a drag-reducing surfactant on a turbulent boundary layer was investigated using a PIV system. PIV measurements were made for a momentum thickness Reynolds number, Re_0(= U_eθ/ν)= 480, where U_e, θ and ν are the free-stream velocity, momentum thickness and kinematic viscosity, respectively. Results of PIV measurement agreed well with those of LDV. PIV measurements showed that the streamwise and wall-normal turbulence intensities and Reynolds shear stress of the surfactant solution were smaller than those of water, respectively, as well as LDV measurements. Fluctuating velocity vector fields of the surfactant solution indicated that there was few near-wall coherent structures as in the case of the canonical wall-bounded turbulent flow.
