翅尖轨迹对食蚜蝇悬停时气动特性的影响

食蚜蝇悬停飞行时的抬升角相对较小，在上下拍起始和结束时刻要比拍动中部的大，这样就使得翅尖的拍动轨迹呈现出浅“U”形。为了分析该翅尖轨迹是否会对其气动特性产生影响，利用计算流体力学的方法分别计算了4只食蚜蝇在考虑抬升角和忽略抬升角2种情形下的气动力，分析对比了2种情形下的不同时刻绕翅膀的瞬时流线，并计算比较了2种情形下气动功率系数与平均举力系数的比值。研究结果表明:抬升角的存在会使其维持体重所需的举力增加10%左右；举力增大的同时能耗却比忽略抬升角情形下要低3%左右。 

Effect of wing-tip trajectory on aerodynamics of hovering true hoverfly

For the hovering true hoverfly, stroke deviation angle is relatively small. It is higher at the beginning and end of a downstroke or upstroke, and lower at the middle of the downstroke or upstroke, which leads to a shallow U-shaped wing-tip trajectory. In order to investigate the effect of wing-tip trajectory on the aerodynamics, the measured wing kinematics with deviation angle (or without deviation angle) was used in a computational fluid dynamics method to compute the aerodynamic forces and moments acting on 4 hoverfies. Streamline of the two types of wing-tip trajectory was plotted at spanwise location in the different time of one stroke cycle. The aerodynamic power requirement was computed using the aerodynamic moment. The power coefficients and mean vertical force coefficients of two types of wing-tip trajectories were compared. The results show that the weight-supporting force with deviation angle is approximately 10% larger than that without deviation angle, but the power requirement with deviation angle is approximately 3% less than that without deviation angle.