湍流边界层内表面活性剂减阻特性研究

Study on drag reduction characteristics of surfactants in turbulent boundary layer

湍流主要通过边界层流体与壁面的摩擦引起的,因此,研究表面活性剂的流向上边界层内湍流减阻性非常有意义,通过压降和粒子图像测速法分别研究了质量分数为10×10^-6,50×10^-6和100×10^-6下的表面活性剂溶液与水的压降、范宁系数、减阻率、平均速度、速度分布云图、雷诺应力、涡量和涡量分布云图,实验发现:在表面活性剂的壁面范宁系数要比水时壁面的范宁系数要小,在质量分数为50×10^-6时减阻效果最好,最大减阻率为20%。得出结论:表面活性剂的加入使湍流边界层的厚度增加,雷诺切应力减小,在靠近管道的中心处的涡量最小,随着远离管道的中心,涡量缓慢地增大,近壁区的涡量降低,表面活性剂的减阻溶液的涡量比水的涡量稍微大一点,说明主要抑制管道中心区域的湍流强度来降低阻力,从而达到减阻效果。

Turbulence is mainly caused by the friction between fluid and the wall surface in the boundary layer.Therefore,it is great significant to study the turbulent drag reduction of surfactant inflow direction of the upper boundary layer.The pressure drop,Fanning coefficient,drag reduction rate,average velocity,velocity distribution,Reynolds stress,vorticity and vorticity distribution of water and surfactant solution at mass fraction 10×10^-6,50×10^-6 and 100×10^-6 were studied by pressure drop and particle image velocimetry,respectively.It is found that the wall surfactant′s fanning coefficient is smaller than water′s,and the drag reduction effect is the best when the concentration is 50×10^-6,and the maximum drag reduction rate is 20%.It is concluded that the addition of surfactant makes the turbulent boundary layer thickness increase.The Reynolds shear stress and the vorticity decrease near the pipe center.With the distance increases from the pipe center,the vorticity increases slowly.However the vorticity near the wall decreases and the vorticity of the surfactant drag reducing solution is slightly larger than water′s.It is shown that the resistance can be reduced and the drag reduction effect can be achieved by suppressing the turbulence intensity in the pipeline central region.