| Summary: | 碩士 === 淡江大學 === 航空太空工程學系碩士班 === 102 === 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.
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