Turbulence transport of surfactant solution flow during drag reduction degeneration

Turbulence transport of surfactant solution flow during drag reduction degeneration is investigated experimentally in a two-dimensional channel. Particle Image Velocimetry (PIV) system is used to take two-dimensional velocity frames in the stream-wise and wall-normal plane. The additive of surfactant is cetyltrimethyl ammonium chloride (CTAC) with the mass concentration of 25 ppm. Drag reduction degeneration happens in the CTAC solution flow, exhibiting the maximal drag reduction at Re = 25 000 and losing drag reduction completely at Re = 40 000. The velocity frames are statistically analyzed in four quadrants which are divided by the u-axis and v axis. It is found that the phenomenon of “Zero Reynolds shear stress” is caused by the decrease of wall-normal fluctuations and its symmetrical distribution in quadrants. The increase of Reynolds number leads to the enhancement of turbulence burst phenomenon. During the drag reduction degeneration, the CTAC solution flow contains both high turbulence intensity and drag reduction states.