Abstract:

A systematic study on the turbulent flow of surfactant solutions in different wide-rib rectangular microgroove channels was carried out by direct numerical simulation. The results showed that the drag reduction performance of surfactant solutions could be further enhanced in the grooved channel with a suitable groove size. The optimal size of microgroove for drag reduction could be enlarged in the surfactant solution. The collaborative drag reduction effect of surfactant solution in grooved channel was mainly the competition result of the “restriction effect” and the “tip effect” of the microgroove. There was a higher shear stress near the grooved tips, but the stress was very small within the grooved valley. If the microgroove not only prevents the near-wall vortices from intruding into the grooved valley effectively, but also presents a better restriction effect on the spanwise motions of the near-wall streamwise vortices, the microgroove will show a drag reduction enhancement effect. On the contrary, if the size of microgroove increases too large to prevent the near-wall vortices from intruding into the grooved valley, the shear stress near grooved tip and within grooved valley will increase, and the microgroove will show drag-increasing performance. The fact that a large number of small and weak secondary streamwise vortices induced in the grooved valley is the key factor to increase the restriction effect and thus enhance the drag reduction of surfactant solutions.

Key words: surfactants, turbulent flow, microgroove, numerical simulation, collaborative drag reduction

摘要：

采用直接数值模拟方法对表面活性剂溶液在不同尺寸宽肋矩形微沟槽通道内的湍流流动进行了数值模拟研究。结果表明表面活性剂溶液的减阻性能在合适尺寸的微沟槽通道内能进一步得到强化，同时微沟槽的最优减阻尺寸在表面活性剂溶液中也可以得到放大；表面活性剂溶液在微沟槽通道内的协同减阻强化效果是由微沟槽的“约束作用”和“尖峰作用”这两个主要因素相互博弈的结果。微沟槽尖峰处具有较高的剪切应力，槽谷内部剪切应力很小。当微沟槽能有效防止近壁湍流涡侵入槽谷内部，且又能对部分流向涡的展向运动起到较好的约束作用时，微沟槽将表现出减阻强化性能，反之则会出现增阻性能。微沟槽在槽谷内诱导的数量多、尺寸小且旋转强度弱的二次流向涡是其在表面活性剂溶液中能增大“约束作用”和发挥减阻强化性能的本质因素。

关键词: 表面活性剂, 湍流, 微沟槽, 数值模拟, 协同减阻