An experimental study of surfactant effects on spilling breakers
An experimental study of surfactant effects on spilling breakers
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DOI：
10.1017/s0022112006002011
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发表时间：
2006-11-25
影响因子：
3.7
通讯作者：
Duncan, James H.
中科院分区：
文献类型：
--
作者：
Liu, Xinan;Duncan, James H.
实验研究了表面活性剂存在时溢流破碎器的动力学行为。溢出断路器产生弗劳德规模的机械产生的分散集中波包的平均频率为1.15，1.26和1.42赫兹。分别进行了实验，相同的造波机运动在干净的水和水中的各种散装浓度的可溶性表面活性剂十二烷基硫酸钠（SDS）和Triton X-100（TX）。对于几乎所有的表面活性剂的条件下，表面压力等温线，平衡表面弹性和表面粘度原位测量，以表征自由表面的动态性能。在干净的水中，这里考虑的所有波浪都是在没有自由表面翻转的情况下破碎的。这种破碎过程开始于波峰前面的凸起和凸起前缘上游的毛细波（称为趾部）的形成。短时间后，水流在波趾下方分离，并在波趾快速沿波面向下移动时形成湍流。在趾部运动期间，在趾部和顶部之间出现一连串波纹，并且这一连串波纹被扫向下游。在表面活性剂的存在下，凸起的形状被修改，其大小通常随表面活性剂浓度的增加而减小。在清水的情况下，即使在表面活性剂浓度最低的情况下，脚趾上游的毛细波也会急剧减少。使用表面活性剂时，破碎过程的开始仍然是在趾部开始沿着波浪的前向面向下移动时开始的。在破碎过程的这一阶段期间，在波趾和波峰之间产生的波纹图案随表面活性剂的浓度而变化。发现趾部和波峰之间的垂直距离的时间历史与标称长度（sigma（0）/rho g）（1/2）成比例，而从趾部到波峰的凸起长度与标称长度（mu（s）/rho root g）（2/5）成比例，其中sigma（0）和mu（s）分别是环境表面张力和表面粘度。
The dynamics of spilling breakers in the presence of surfactants were studied experimentally. The spilling breakers were produced from Froude-scaled mechanically generated dispersively focused wave packets with average frequencies of 1.15, 1.26 and 1.42 Hz. Separate experiments were performed with the same wave-maker motions in clean water and in water with various bulk concentrations of the soluble surfactants sodium dodecyl sulfate (SDS) and Triton X-100 (TX). For nearly all surfactant conditions, the surface-pressure isotherm, equilibrium surface elasticity and surface viscosity were measured in situ in order to characterize the dynamic properties of the free surface. In clean water, all the waves considered herein break without overturning of the free surface. This breaking process begins with the formation of a bulge on the forward face of the wave crest and capillary waves upstream of the leading edge of the bulge (called the toe). After a short time, the flow separates under the toe and a turbulent flow is developed while the toe moves rapidly down the wave face. During the toe motion, a train of ripples appears between the toe and the crest and this train of ripples is swept downstream. In the presence of surfactants, the bulge shape is modified and its size generally decreases with increasing surfactant concentration. The capillary waves found upstream of the toe in the clean-water case are dramatically reduced at even the lowest concentrations of surfactants. With surfactants, the start of the breaking process is still initiated when the toe begins to move down the forward face of the wave. The pattern of ripples generated between the toe and the crest of the wave during this phase of the breaking process varies with the concentration of surfactant. It was found that the temporal history of the vertical distance between the toe and the wave crest scales with the nominal length (sigma(0)/rho g)(1/2) while the bulge length from toe to crest scales with the nominal length (mu(s)/rho root g)(2/5), where sigma(0) and mu(s) are the ambient surface tension and the surface viscosity, respectively.