槽道内聚合物减阻流动对数层湍流结构的影响

Influence on Turbulent Structure in the Logarithmic Layer of a Drag-reducing Channel Flow with Polymer Additives

为深入阐明聚合物减阻剂对壁湍流的影响,试验研究了聚合物槽道减阻流中近壁对数层的湍流特征结构。高分子聚合物溶液经过多孔壁面缓慢注入槽道,采用立体粒子图像测速技术测量对数层中流向与展向平面内3个方向的速度分量,采用二维粒子图像测速技术测量流向与垂直壁面方向平面的速度场。基于条件平均的方法,发现在对数层存在低动量流体的大尺度条带结构,在黏弹性聚合物溶液的影响下,条带在展向方向上扩展,在流向方向上拉伸;条带周围垂直壁面方向的脉动速度强度明显降低,类喷射运动被显著抑制。

To illuminate the effect of drag-reducing polymer on the wall turbulence, the turbulent structure in near-wall logarithmic layer is experimentally investigated. The polymer solution is injected slowly from the porous wall. The three-directional velocity components in two streamwise spanwise（ x-z） planes located in the logarithmic layer are obtained using stereo particle-image velocimetry（ PIV） in addition to the vectors in a streamwise wall-normal（ x-y） plane measured by two-dimensional PIV. The streamwise large-scale streaky structure of low-momentum fluid is observed in the logarithmic layer using the conditional-averaging method. With the effects of the viscoelastic polymer solutions, the streaky structure is expanded in the z direction and elongated in the x direction. The intensity of wall-normal velocity fluctuation around the streak is found to be depressed.The ejection-like motion on the streak is suppressed dramatically.