Behavior of the Hairpin Votex in a Laminar Boundary Layr of Surfactant Solution

为了阐明表面活性剂溶液湍流减阻机理，实验研究了层流平板边界层中连续涡和孤立涡中毛羽的行为。所得结果如下：[连续产生的发夹涡](1)表面活性剂溶液流动中发夹产生的频率低于水流。(2)在表面活性剂溶液的流动中，涡腿的扭结区和二次涡都很难形成。(3)在下游位置，水流中有多条低速条纹。另一方面，在表面活性剂溶液的流动中只能观察到单一的低速条纹。(4)表面活性剂溶液中涡头对流速度与局部流速之比小于水中。(5)表面活性剂溶液流动中发夹涡颈与壁面夹角较小[单发夹涡](1)为了在表面活性剂溶液流动中产生单发夹涡，感染射流的速度必须更高，持续时间必须更短。(2)当剪切速率高于诱导剪切状态临界值时，表面活性剂溶液流动中不会产生发夹涡。(3)极限条件下可产生单发夹涡。

In order to clarify the mechanism of drag-reduction in the turbulent flow of a surfactant solution, the behavior of hairp in vortex generated continuously or solitary in a laminar flat-plate boundary layr was investigated experimentally. The results obtainedare as follows.[continuously generated hairpin vortex](1)The frequency of hairpin generation is lower in the flow of surfactant solution than in the water flow.(2)In the flow of surfactant solution, both the kinked region of the vortex legs and the secondary votex are hard to develop.(3)At downsream location, multiple low-speed streaks are observed in the water flow. On the other hand, only single low -speed streak can be observed in the flow of surfactant solution.(4)The ratio of the convecting velocity of the vortex head to the local flow velocity is smaller in the surfactant solution thon in the water.(5)The angle between the neck of hairpin vortex and the wall is smaller in the flow of surfactant solution[single hairpin vortex](1)In order to generate a single hairpin vortex in the flow of surfactant solution, the speed of the infecting jet must be higher and the duration time must be shorter.(2)The hairpin vortex in the flow of surfactant solution does not develop if the shear rate is higher than the critical value for the shear inducing state.(3)The single hairpin vortex can be generated for the limiting conditions.