柔性翼對開合機制之空氣動力學的研究

Abstract

昆蟲經過長久的演化，發展出各種相當巧妙的飛行方式。其中Weis-Fogh在1973年藉由觀察小黃蜂而發現能產生高升力的開合機制。許多學者多以剛性翼模型來模擬雙翅的開合機制，但是卻很少人考慮到昆蟲翅膀的柔性問題，進而探討柔性翅膀對於空氣動力學之影響。有鑒於此，本文以研究小黃蜂的高升力開合機制為主，使用剛性翼(壓克力)並配合不同硬度的柔性翼(翻模矽膠)來作為實驗的翼板，以期望找出昆蟲演化出柔性翼之主因。同時，採用具高升力的開合機制進行研究，比較分析不同硬度的翼板在相同的動作下，其受力情況之差異性，以找出各自的優缺點。 本實驗使用機械手臂配合伺服馬達，在實驗水槽中模擬開合機制的運動模式。為了符合真實昆蟲撲拍的雷諾數，實驗流體使用甘油與水的混合，使得雷諾數為 。翼板總共有五種硬度，而開合機制採用對稱式，實驗中轉動角度由10度增加到80度，間隔10度，史徹赫數 。藉由量力裝置量測不同轉動角度下的開合機制受力圖，來研究開合機制的高升力來源，並探討翼板的柔性對開合機制的影響，以及雙翼對比單翼的升力增益，並實驗升力增益與翼板柔性間的關係。 本實驗結果顯示，柔性翼可產生與剛性翼一樣大的升力，但是拍動時產生的阻力卻小得多，且在各攻角的平均升力表現較佳，證明了昆蟲為何演化成柔性翼的原因。

Insects had developed many flying technique through longstanding evolution. In 1973, Weis-Fogh found a novel mode called ”clap-fling mechanism” which can pro-duce high lift. There are many researchers use rigid body to simulate the clap-fling mechanism of two wing configuration. But few considered the flexibility of insect wings and its influence to aerodynamics problem. Therefore, we focus on the high-lift mechanism of wasp Encarsia in this study. Then, we use the rigid airfoil (acrylic) and flexible wings (silica gel) as the experimental wings in order to figure out the reason how does the insect evolve into flexible wing. In the meanwhile, we can investigate the discrepancy of acting force by different flexibility of airfoil, and also discovers each advantage and their shortcoming. For the experiment setup, we use single-axis robot arms mounted on sevo motors, and simulate the motion of clap and fling in the experimental tank. In order to fit the Reynolds number for real insect flapping, the mixture of water and glycerine was used as the experiment fluid and the Reynolds number is around 90. There are five differ-ent flexibility of airfoil, the motion of clap and fling was set to be symmetric mode, and the attack angle varies from 100 ~ 800 with 100 increment, the Strouhal num-ber St= 0.1~0.5. We can measure the acting force by force sensor for different attack angles to discover the source of high-lift generation during the clap-fling motion. And look into the impact on the wing flexibility for clap-fling mechanism. Moreover, it can compare the lift enhancement between two wings and single wing, and also observe the lift enhancement related to the flexibility of the airfoil. The results indicated that the flexible wing can produce the same lift as the rigid wing, and the drag force is much smaller than that of the single wing under the same condition. In addition, the performance of lift in average is better for each attack angle. This phenomenon can support advantageous evidence that the insect evolved into flexible wings.