DRAG REDUCTION BY COMBINED EFFECT OF SURFACTANT AND MICROGROOVES IN A PIPE FLOW

Technologies of drag reduction on surfactant and microgrooves drag reduction have been studied separately for decades. However, there are only few studies on the combined effect of surfactant and microgrooves. For the great potential benefit of its application on practical pipeline transportation, in the present work the collaborative drag reduction of surfactant and microgrooves was studied experimentally by flow visualization. The drag reduction performances of water and hexadecyl trimethyl ammonium chloride (CTAC) solution that flow over smooth and microgrooved plates were evaluated and compared with pressure drop experiments. The particle imaging velocity (PIV) measurement system was employed to analyze the structure of the turbulent flow. The combined effect of surfactant and microgrooves on turbulent drag reduction was shown with the detailed velocity field including instantaneous mean velocity, Reynolds shear stress, velocity fluctuation intensity, and vorticity. Compared with smooth plate, it was verified in this experiment that microgrooves can accelerate the formation and destruction of shear-induced structures (SIS) in the surfactant solution at different Reynolds numbers, which improved the drag reduction rate of surfactant solution. Moreover, the SIS formed in the surfactant solution can restrict the evolution of turbulent vortices in the near-wall region and provided a more stable and effective flow environment when microgrooves start reducing drag, which indicates that SIS can expand the range of using drag reduction microgrooves.