中文摘要：

昆虫起飞的气动机理研究对于微型飞行器（MAV）的设计具有重要的参考意义。本文基于前人对果蝇自由起飞阶段测得的实验结果，构建了翼的二维模型和运动方程。采用人工伪压缩方法求解非定常不可压缩NS方程组，通过分析流场涡结构的发展演化和压强变化对流体动力的影响，深入研究了非定常气动力的产生过程，并探讨了翻转模式和下拍时间比对于气动性能的影响。结果表明：自由起飞的第一次挥拍对果蝇的自由起飞具有重要的影响。其中第一次下拍采用了大的超前比率和小的下拍时间比，这使得第一次下拍产生了很高的升力。果蝇自由起飞中翼翻转普遍采用了超前模式，大的超前比率和小的下拍时间比可以产生很高的升力。

英文摘要：

The investigation for the aerodynamic mechanisms of the flapping wing during insect flight has important reference value for the design of MAV. In recent years, people have made great progress in the study of the flight mechanisms of insects in hover and forward flight. However, as the unsteady flow of flapping wing is rather complex, the research for the unsteady flow during the take-off stage is still in its infancy. The aerodynamic performance of the flapping wing of Drosophila during the free take-off is inves- tigated. The main concentration of this study lies in two aspects, the construction of the physical mode for the flapping wing and the analysis of unsteady flow during the take-off phase. First, a two-dimensional model and equations of motion based on the measured results during the free take-off stage of the fruit fly are constructed. Then the information of the flow field by numerical simulation and the generating process of the unsteady aerodynamic force are investigated. Finally, the effects of flapping mode and downstroke duration ratio for the aerodynamic performance are analyzed. The results show= in a free take-off flight, the first flap has a significant impact on the voluntary take-off, drosophila adopt advance mode generally, large advance ratio and small downstroke duration ratio can produce a high lift.