Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil
Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil
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DOI：
10.1088/1748-3182/7/3/036003
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发表时间：
2012-09-01
影响因子：
3.4
通讯作者：
Gopalarathnam, Ashok
中科院分区：
文献类型：
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作者：
Johnston, Joe;Gopalarathnam, Ashok
安装在机翼上表面的襟翼被称为“升力增强效应器”，风洞测试显示其具有与鸟类的隐性羽毛类似的功能，鸟类的隐性羽毛会响应分离的气流而从机翼表面升起。效应器由薄聚酯薄膜制成，可以绕其前缘自由旋转。测试在 NCSU 亚音速风洞中进行，弦雷诺数为 4 x 10(5)。效应器的最大升力系数与干净翼型的最大升力系数相同，但在 12 度到几乎 20 度的迎角范围内保持不变，从而导致非常温和的失速行为。为了更好地了解空气动力学并估计自由移动效应器的展开角度，还测试了由硬木制成的固定角度效应器。观察到失速迎角随着效应器角度的增加而逐渐增加，效应器角度超过 60 度时收益递减。对自由移动和固定效应器的阻力测试表明，高迎角时的阻力有显着改善。使用和不使用固定角度效应器的机翼上的油流可视化证明，与干净的机翼相比，效应器导致分离点在机翼上向后移动。这被认为是效应器提高升力和阻力的主要机制。固定效应器与自由效应器测试结果的比较表明，自由效应器的展开角度在30度到45度之间。当在干净翼型的失速角或超出其失速角运行时，自由效应器会随着迎角的增加而自动部署到逐渐更高的角度。这减慢了分离点向上游的快速移动，并避免了在失速开始时在清洁翼型上看到的升力系数的严重降低和阻力系数的增加。因此，效应器将失速推迟 4-8 度，并使失速行为更加温和。使用效应器的好处包括在栖息和机动飞行期间以大迎角进行无忧无虑的操作，特别是在阵风条件下。
A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 x 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12 degrees to almost 20 degrees, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60 degrees. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30 degrees and 45 degrees. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8 degrees and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.