Turbulent mass transfer in a drag-reducing channel flow with dosed polymer solution by simultaneous PIV and PLIF measurements

Turbulent mass transfer in a drag-reducing channel flow by dosed polymer solution was investigated experimentally by simultaneous PIV and PLIF measurements. To discuss the relationship between mass transfer and momentum transportation, turbulent Schmidt number was computed. Reynolds number based on the channel height was set to 40000 and poly(ethylene oxide) was used as a polymer. The polymer solution with 25 and 100 ppm of weight concentration was dosed at 10.5 L/min from the whole surface of the channel wall. As a result, in the case of water flow, dosed dyed water was ejected from the wall and was well diffused by the strong turbulent eddy motion. In contrast, when the polymer solution was dosed from the wall, the diffusion was largely suppressed in the near-wall region and drag reduction occurred. The turbulent Schmidt number largely increases over 1 in the near-wall region.