Lang Amy W, Jones Emily M, Afroz Farhana
Department of Aerospace Engineering and Mechanics, University of Alabama, 255 H M Comer, 245 7th Avenue, Box 870280, Tuscaloosa, AL 35487, United States of America.
Bioinspir Biomim. 2017 Feb 10;12(2):026005. doi: 10.1088/1748-3190/aa5770.
Over many decades the biological surfaces of aquatic swimmers have been studied for their potential as drag reducing surfaces. The hydrodynamic benefit of riblets, or grooves embedded parallel to the flow which appear on surfaces such as shark skin, have been well documented. However the skin of dolphins is embedded with sinusoidal grooves that run perpendicular or transverse to the flow over their bodies. It is theorized that the transverse grooves present on dolphin skin trap vortices between them, creating a partial slip condition over the surface and inducing turbulence augmentation in the boundary layer, thus acting as a potential mechanism to reduce flow separation and thus pressure drag. In an attempt to test this hypothesis and study these effects, an adverse pressure gradient was induced above a flat plate resulting in a controlled region of flow separation occurring within a tripped, turbulent boundary layer. Small transverse grooves of both rectangular and sinusoidal shape were 3D printed and mounted to the plate to measure their effect on the boundary layer flow. The results were compared to a flat plate without grooves using digital particle image velocimetry (DPIV). The strength of the adverse pressure gradient was varied, and the observed control in flow separation and other effects upon the boundary layer are discussed.
几十年来，水生游泳者的生物表面因其作为减阻表面的潜力而受到研究。脊状突起，即平行于水流嵌入的凹槽，出现在鲨鱼皮等表面上，其流体动力学益处已有充分记录。然而，海豚的皮肤嵌有正弦形凹槽，这些凹槽垂直于或横向于其身体上的水流方向。从理论上讲，海豚皮肤上的横向凹槽在它们之间捕获涡旋，在表面上形成部分滑移条件，并在边界层中引发湍流增强，从而作为减少流动分离进而降低压力阻力的潜在机制。为了验证这一假设并研究这些影响，在平板上方诱导了不利压力梯度，导致在触发的湍流边界层内出现可控的流动分离区域。将矩形和正弦形的小横向凹槽进行3D打印并安装到平板上，以测量它们对边界层流动的影响。使用数字粒子图像测速技术（DPIV）将结果与没有凹槽的平板进行比较。改变不利压力梯度的强度，并讨论观察到的流动分离控制以及对边界层的其他影响。
