Abstract
The vortex structures in drag reducing fluids were investigated in transitional and turbulent boundary layer respectively. Using a vibrating ribbon method, two-dimensional disturbance was introduced into the transitional flow, and its growth was observed. The instantaneous velocity distribution was obtained using PIV. The drag reducing additives produced similar change in vortex structure in the transitional flow and the turbulent flow. The polymer additives suppressed the growth of the vortex and its lift up in the transition and the turbulent flow. The surfactant solutions brought out the maximum drag reduction in the turbulent flow, and inhibited vortex structure in the transitional and the turbulent flow. These observations suggest the similarity between the mechanism of turbulence modification in the transitional and the turbulent flow.
