| Abstract: | 近年來拍翼微飛行器變得越來越受重視，也使得更多人投入微飛行器的研究，但大多數微型拍翼飛行器研究都是分析在晴天下飛行的蟲類及小型鳥類。過去幾年間，台灣曾發生許多因惡劣天氣所引發的災害，如像是極大量的暴雨或是使人困在山區的濃霧等情況，在這些特殊情況下，使用微型拍翼飛行器來進行偵測或是協助搜救能顯著的增加救難效率。雖然微型拍翼飛行器能靈活的運動，但也因為其輕巧、靈活的特性，在飛行過程中非常容易受到周遭大氣環境變化的影響。因此，微型拍翼飛行器在特殊大氣環境下飛行性能變化是本研究團隊長期研究的一項重要課題。
在本研究中我們依據名為Morpho peleides的蝴蝶建立其幾何外形，使用GAMBIT和ANSYS前處理軟體產生網格，並結合軟體FLUENT中UDF(User Define Function)及動態網格機制來模擬蝴蝶在不同攻角的拍翼飛行，大雨計算則是運用FLUENT內建DPM模組(Discrete Phase Model)來模擬蝴蝶在惡劣天氣下飛行空氣動力性能變化。
本研究中吾人嘗試使用四種不同網格數的網格來進行驗證，結果不管是在升力係數還是阻力係數全都得出相近且幾乎一樣的數值。根據幾個蝴蝶固定在不同攻角下晴天飛行的結果，我們得知當蝴蝶在飛行時隨著攻角的上升，整個拍動週期的平均升力也會跟著增加，且升力係數曲線的趨勢會與真實擺動身體飛行的蝴蝶更加近似。最後我們比較在晴天及大雨下的飛行狀況，蝴蝶在大雨的情況下飛行，升力係數會較晴空時顯著的下降，並且升力減少的百分比會隨著攻角的上升而減少。在降雨量為25 g/m3時，升力減少的百分比會從618.6%減少至60.389%。當降雨量為39 g/m3時，則會從1057%降至101.537%。因此，吾人認為拍翼飛行受到大雨的影響程度可以透過提高拍翼的攻角而得到緩解。
In recent years, flapping wing technology is becoming more popular, and Micro Air Vehicle (MAV) has received great attention from researchers. For most people their desired MAV performance is limited in the flapping mode of small birds and insects under clear weather situation. But in past years Taiwan has experienced many disasters caused by detrimental and severe weather, such as extremely heavy rain and very thick fog. In such cases if MAV could put into use to help the rescue mission, it could significantly improve the efficiency of rescue. However, the insect-like MAV is very small and light, and it''s very sensitive to sudden change of atmospheric surroundings. Therefore, maintain the flapping wing MAV flight quality in extreme weather will be an important issue.
In this study, we constructed a geometric model of the butterfly based on a true Morpho peleides and created a grid system by GAMBIT and ANSYS preprocessing software, then use the CFD software FLUENT combine with the User Define Function (UDF) to analyze the relationship between the flow field and other aerodynamic phenomenon. For our simulation, we programing a grid convergence process first to verify the simulation of our 3-D butterfly flapping motion, and the flapping-wing aerodynamic parameters such as lift coefficient and drag coefficient are almost same with four grid systems in clam atmospheric condition.
According to several cases, we can find some result. When the butterfly increases the pitch angle of flapping motion in forward flight, the lift coefficient will increase too. Then the trend of the lift coefficient curve will more approximate with the lift coefficient of the true butterfly in forward flight. In our abnormal atmospheric cases, we used the Discrete Particles Model (DPM) in FLUENT to simulate the 3-D butterfly flapping motion in heavy rain condition. In our result, the average values of lift coefficient under the heavy rain condition are lower than the case in normal atmospheric condition. When the liquid water content (LWC) is 25 g/m3, the reduction rate of lift coefficient would be reduced to 60.389% from 618.6% with the rising angle of attack. In the situation of the liquid water content is 39 g/m3, the reduction rate of lift coefficient will decrease from 1057% to 101.537% with the gradual increase in the angle of attack. Therefore, the effect of the heavy rain can be relieved by changing the angle of attack in forward flight, and the higher angle of attack can relieve more impact of heavy rain. |
