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摘要:
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。
Abstract: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.
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Key words:
- wing-tip trajectory /
- hoverfly /
- hovering flight /
- aerodynamics /
- power
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图 2 拍动平面与翅膀拍动姿态角的定义
Figure 2. Definition of flapping plane and flapping wing attitude angle
图 4 2种翅尖轨迹的CV、CH、CL和CD在一个拍动周期内的变化曲线
Figure 4. Times courses of computed coefficients CV, CH, CL and CD of HF1 in one cycle
图 5 2种翅尖轨迹在
Figure 5. Streamline plots at spanwise location r2 at
图 6 2种翅尖轨迹在
Figure 6. Streamline plots at spanwise location r2 at
图 7 HF1真实翅尖轨迹的抬升角及无量纲抬升角速度曲线
Figure 7. Curves of deviation angle and non-dimensional deviation angular velocity of HF1 in real wing tip trajectory
图 8 各坐标轴角速度矢量示意图
Figure 8. Schematic diagram of angular velocity vector in different axes
表 1 4只食蚜蝇2种翅尖轨迹的平均举力系数和平均水平力系数
Table 1. Mean vertical and horizontal force coefficients of four hoverflies in two types of wing-tip trajectories
翅尖轨迹情形 HF1 HF2 HF3 HF4 CV CH CV CH CV CH CV CH Normal 1.40 0.40 1.67 -0.09 1.52 0.31 1.70 0.35 Real 1.63 0.38 1.85 -0.11 1.70 0.29 1.71 0.35 
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表 2 4只食蚜蝇2种翅尖轨迹气动功率系数与平均举力系数的比值
Table 2. Ratio of aerodynamic power coefficient to mean vertical force coefficient of four hoverflies in two types of wing-tip trajectories
翅尖轨迹情形 CW, a/CV HF1 HF2 HF3 HF4 Normal 9.00 8.82 10.14 10.63 Real 8.69 8.45 9.88 10.22
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