Analysis of organized turbulent structure by pattern recognition technique in drag-reducing surfactant solution flow in a channel

The turbulent transport of heat and momentum is largely decreased by adding surfactant or water-soluble long-chain polymer into water flow. In the present study, we investigated the well-ordered structures in the near-wall region and determined their variations due to modulated turbulence by viscoelasticity of surfactant solution. We used a PIV system to perform a trajectory analysis, which allow us to capture the organized structure by pattern recognition on transition in four quadrants of velocity fluctuations in turbulent channel flow. We examined various flow patterns in the surfactant solution flow. The mean persistence lengths of quadrant contributing turbulent drag decreases in size and the Reynolds shear stress of high amplitude happens intermittently. Moreover, this tendency is induced by different vortex structure compared with the water flow. The decrease of heat transfer should be attributed to this change of dominant vortical structure.