Fluid drag reduction by penguin-mimetic laser-ablated riblets with yaw angles
Fluid drag reduction by penguin-mimetic laser-ablated riblets with yaw angles
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DOI：
10.1088/1748-3190/ac7f71
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发表时间：
2022-07
影响因子：
3.4
通讯作者：
Ryosuke Saito;Takeshi Yamasaki;Hiroto Tanaka
中科院分区：
文献类型：
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作者：
Ryosuke Saito;Takeshi Yamasaki;Hiroto Tanaka
企鹅在水下觅食，身体上覆盖着浓密的羽毛，其中的倒刺是纵向的。我们假设这些倒钩起到了波纹的作用，减少了游泳时的摩擦阻力。考虑到各种真实的游泳条件，减阻效果有望在流速和相对于水流的偏航角变化下保持稳定。为了验证这一假设，我们根据这些倒刺的形态制造了梯形的条纹，并在水洞中测量了用这些制造的条纹的平板的阻力。倒刺的间距、宽度和高度分别约为100 μm、60 μm和30 μm。对于一个典型的企鹅游泳速度为1.4 m s−1时，这个间距导致了5.5的无量纲间距。利用紫外激光烧蚀技术在聚酰亚胺薄膜上制备了四种类型的微纹。首先是将小波纹的间距减小到41 μm，模拟水洞中通常和慢速游动行为的表面流动情况。另外三种是按照真实倒刺的实际尺寸制造的（间距为100 μm），肋骨宽度分别为10、25和50 μm。用实际尺寸的波纹测试了0°、15°、30°和45°的偏航角。最小s +为1.59时，小波纹的减阻率达到了1.97%。对于所有三种实际尺寸的膛线，将偏航角从0°增加到15°可以提高整个s +范围内的减阻率，最高可达13.5°。窄脊纹在更高的偏航角（45°）下降低阻力，但在零偏航角时阻力增加。总的来说，作为倒刺代表的中脊纹是平衡的。
The bodies of penguins, which swim underwater to forage, are densely covered with feathers, in which the barbs are oriented in the longitudinal direction. We hypothesize that these barbs act as riblets and reduce friction drag during swimming. Considering various real-world swim conditions, the drag reduction effect is expected to be robust against changes in the flow speed and yaw angle relative to the flow. To test this hypothesis, we created trapezoidal riblets based on the morphology of these barbs and measured the drag of flat plates with these fabricated riblets in a water tunnel. The spacing, width, and height of the barbs were found to be approximately 100, 60, and 30 μm, respectively. This spacing resulted in a nondimensional spacing s + of 5.5 for a typical penguin swimming speed of 1.4 m s−1. We fabricated four types of riblets on polyimide films by ultraviolet laser ablation. The first was a small-scale riblet for which the spacing was decreased to 41 μm to simulate the surface flow condition of the usual and slower swim behaviors in our water tunnel. The other three were manufactured to the actual scale of real barbs (spacing of 100 μm) with three different rib ridge widths: 10, 25, and 50 μm. Yaw angles of 0°, 15°, 30°, and 45° were also tested with the actual-scale riblets. The drag reduction rate of the small-scale riblet was maximized to 1.97% by the smallest s + of 1.59. For all three actual-scale riblets, increasing the yaw angle from zero to 15° enhanced the drag reduction rate for the full range of s + up to 13.5. The narrow-ridge riblet reduced drag at an even higher yaw angle of 45°, but the drag increased with zero yaw angle. Overall, the medium-ridge riblet, which was representative of the barbs, was well-balanced.