Instantaneous Turbulent Structure Relating to Momentum and Scalar Transport in a Reducing Channel Flow With Surfactant Additives

Turbulent surfactant solution flows dramatically suppress turbulent scalar and momentum transports with changes to turbulent structures near the wall. In this study, particle image velocimetry and planar laser induced fluorescence concentration measurement method were used simultaneously to analyze turbulent mass transfer experimentally in surfactant channel flows at high Reynolds number. When compared against the instantaneous flow fields of the water case, the results showed a decrease in the magnitude of elementary vortices in the near-wall region. Momentum and scalar transports are caused by the combination of elementary vortices that are irregularly arranged at the outer edge of the shear layer. A conceptual vortex model is proposed for turbulent scalar transfer that provides a partial explanation for the turbulence statistics of a surfactant solution flow, such as the Reynolds shear stress, turbulent mass flux, and mean concentration distribution.