A surfactant is well known as an additive that brings about drag-reduction in straight (non-swirling) pipe flow. However in industrial applications of the drag-reducing effect, many flow fields exist including the straight pipe flow. The purpose of this study is to investigate the flow characteristics of surfactant solution swirling pipe flow. The drag reducing effect is estimated from the measurement wall pressure loss and the velocity profiles on various pipe sections are measured by 2 dimensional LDV. Since the surfactant solution has viscoelasticity, interesting flow characteristics are shown. The decay of swirl, the vortex type and the turbulence intensity are discussed, compared with the water swirling flow. The oscillating of vortex core is also investigated.

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