Experimental study on drag-reducing turbulent boundary layer flows of surfactant solutions

In this study, the influence of a drag-reducing surfactant on the turbulent boundary layer under different solution concentrations and temperatures was extensively investigated using a two-component laser-Doppler velocimetry system. It is found that the drag reduction ratio DR at the temperature T = 20 degrees C becomes larger downstream, and decreases with the increase of concentration from C = 65 to 150 ppm. The DR for C = 100 ppm becomes smaller with the increase of the temperature from T = 25 to 35 degrees C, and the DR at T = 20 degrees C is smaller than DR at T = 25 degrees C. For the different solution concentrations and temperatures, the value of the mean velocity scaled by the friction velocity increases with increasing the amount of drag reduction. For the present experimental conditions tested, the peak value of streamwise turbulence intensity seems to be not related to the amount of DR directly and to be affected by the low Reynolds number effect strongly.