Investigation of the drag reduction of hydrolyzed polyacrylamide–xanthan gum composite solution in turbulent flow

In this paper, the rheological properties, drag reduction properties, and flow field characteristics of hydrolyzed polyacrylamide (HPAM) solution, xanthan gum (XG) solution, and HPAM–XG composite solution were analyzed to explore the synergistic effect of flexible and rigid polymer. The experimental results show that the viscoelasticity and shear thinning of the composite solution are significantly enhanced compared with single‐component solution, which indicates that the rigid XG has an effect on the viscoelasticity of the flexible HPAM solution. Compared with the single‐component solution, the drag reduction rate of HPAM–XG composite solution is higher, and the mean flow field of HPAM–XG composite solution changes less after being sheared for 300 minutes, which means that not only the drag reduction effect of composite solution is better, but also the shear resistance. Compared with single‐component solution, the mean velocity distribution of the composite solution moves upwards most obviously in the logarithmic layer, the peak of velocity fluctuation in the main flow direction of composite solution is higher, the suppression degree of normal velocity fluctuation is deepened, and the corresponding vorticity intensity is also reduced. These changes in the flow field characteristics explain the reason for the drag reduction gain of the composite solution.